Test 2 Flashcards
(218 cards)
1
Q
What’s the structure of a cell membrane? (plasma membrane)
A
Is made up of the amphipathic (charged and uncharged) phospholipid bilayer. Contains proteins & certain steroid lipids embedded in it
2
Q
What are the functions of the cell membrane?
A
-provides structural basis for metabolic order (keeps together groups of enzymes of the same metabolic pathway) and separates other enzymatic systems
-separates living cells from their surroundings
-takes up required substances and disposes of the unwanted waste
3
Q
What’s the fluid mosaic model?
A
-It describes the structure of the plasma membrane as a mosaic of components
-both phospholipids & proteins move laterally (rarely vertically)
-embedded & surface proteins interspersed throughout the bilayer
4
Q
Can you briefly describe a
key experiment that helped elucidate the model?
A
-Plasma membrane proteins on both mouse and human cells were labelled differently then the cells were fused together
-Results: hybrid cells with mixed proteins which proved that some plasma membranes can move around the plasma membrane
5
Q
What does membrane fluidity depend on, and what happens to the membrane when it’s hot or cold?
A
-fluidity of membrane depends on lipid components
-more double carbon bonds = less fluid
-Hotter temps means too fluid and won’t hold shape
-Colder temps means rigid, not as flexible and may possibly break
6
Q
What’s the the relationship between membrane fluidity and
membrane permeability?
A
Lower membrane fluidity will reduce permeability the reducing it’s ability to take in a push out molecules
7
Q
What’s the relationship between membrane fluidity and temperature?
A
-When temperature increases (hotter), the membrane becomes too fluid/flexible and it won’t hold shape
-When temperature decreases (colder), the membrane becomes rigid, not as fluid and it may break
8
Q
What’s the relationship between membrane fluidity and saturation of fatty acids in phospholipids?
A
-Some organisms will alter the fatty acid content of their membrane lipids to compensate for temp changes
-Homeoviscous adaptation; temp decreases then the proportion of fatty acids increases so the membrane remains fluid
9
Q
What’s the relationship between membrane fluidity and fatty acid length in phospholipids?
A
-Longer fatty acid chains makes the membrane less fluid because of the increase of the van der waals interactions between chains
10
Q
Practice question: What will happen to membrane fluidity if # of double bonds in fatty acids is increased?
A
-decreases fluidity
11
Q
Practice question 2: What will happen to the membrane fluidity if the length of fatty acid chains is increased?
A
-Becomes less fluid because of increase in van der waal interactions b/w chains
12
Q
What’s the relationship between membrane fluidity and the amount of cholesterol?
A
-cholesterol has different affects on the membrane depending on the temperature
-high temps –> stabilizes membrane by binding cholesterol to the hydrophilic head of an adjacent phospholipid
-low temps –> acts as spacer to prevent van der waal interactions thus increasing fluidity
13
Q
What’s a fluidity buffer?
A
-Fluidity buffer has different affects on the membrane fluidity depending on the temperature
-cholesterol stabilizes the membrane at high temps by bind OH group in cholesterol to adjacent phospholipid head
-cholesterol creates space between membranes at cold temps to prevent van der waal interactions making it more fluid
14
Q
Why have different membrane compositions evolved as adaptations in organisms?
A
Because different organisms live in different environments; different temperatures require different adaptations (homeoviscous adaptation - fatty acids)
15
Q
What are the two classes of membrane proteins?
A
1) integral proteins (inside)
2) peripheral proteins (outside)
16
Q
Describe the integral protein
A
-firmly bound to the inside of the membrane & they penetrate the core of the lipid bilayer
-amphipathic (hydrophilic extends outside of cell or into cytoplasm & hydrophobic interacts w/ fatty acid tails)
-some don’t extend all the way through the membrane others do, these are transmembrane proteins (some can even span the membrane many times)
17
Q
What are some examples of an integral proteins?
A
1) Aquaporins: they transport water in out out of cell down its gradient (osmosis)
2) Glycoproteins: embedded in plasma membrane and the oligosaccharide faces the ECM (A,B,O blood types)
18
Q
describe the peripheral protein
A
-not embedded in the lipid bilayer
-located on the inner or outer surface of the membrane
-may be receptors on the surface of the cell or enzymes associated w/ the inner membrane
19
Q
What are some examples of peripheral proteins?
A
Cytochrome c, cupredoxins, high potential iron protein, adrenodoxin reductase, some flavoproteins
20
Q
What’s a transmembrane protein and explain why they’re amphipathic?
A
They are a type of integral protein that span the entirety of the cell membrane and they’re amphipathic because they extend to the aqueous part of the environment and they interact with the hydrophobic tails
21
Q
why is the bilayer asymmetrical?
A
-Because one of the sides of the membrane has more proteins attached attached to it (more proteins on cytoplasmic side)
-this asymmetry is because of the way each protein is inserted into the bilayer
-each side has specific characteristic due to the proteins attached
22
Q
what is meant by the selective permeability of a membrane?
A
-the membranes ability to differentiate b/w molecules and only letting certain ones in
-this allows them to maintain their internal composition
23
Q
how do proteins and lipids play a role in selective permeability?
A
-transport proteins can move substances in or out of the cell
-longer fatty acid chains makes the membrane more rigid and less permeable
24
Q
What’s the function of an enzyme? And what does its function depend on?
A
-accelerate chemical rxs (organic catalysts)
-function depends on its ability to recognize and bind to some other molecules
25
What's the function of a storage protein?
-provides amino acids to developing embryos
-example: ovalbumin, casein, plants store proteins in seeds
26
What's the function of chemical messenger proteins?
--help coordinate hormones and neurotransmitters
-examples: insulin (hormone excreted by pancreas causing tissues to take up excess glucose), acetylcholine (neurotransmitter used to signal other cells)
27
What's the function of contractile proteins?
-function in movement
-examples: myosin and actin (contraction of muscles)
28
What's the function of defensive proteins?
-defensive substances within the body
-examples:when there's a foreign substance antibodies are made to fight it
29
What's the function of transport proteins?
-move substances within the body or in and out of cells
-example: hemoglobin (moves oxygen from lungs to other tissue)
30
What's the function of receptor proteins?
-regulates response to chemical stimuli
-example: receptors built into membrane of nerve cell used to detect chemical signals from other nerve cells
31
What's the function of structural proteins?
-provides support
-function in cell membrane in muscle tissue, tendons, and ligaments
-examples: collagen and elastin
32
What is passive transport?
-very simple, requires no energy as it goes along the gradient (high to low)
33
What is active transport?
ATP is required as it goes against the gradient (low to high)
34
How are plasma membrane proteins made?
-proteins destined to be peripheral proteins on inner surface are made by free ribosomes in cytoplasm
-proteins destined to be integral or peripheral proteins on outer surface are made by ribosomes in the rough ER
35
How do proteins aid in cell-cell recognition?
-they provide identification tags to cells to distinguish them.
-allows for immune system to recognize & reject foreign cells
-enables cell sorting
36
What is the function of plasmodesmata?
-channels allowing for communication, and transport of water and small molecules b/w plant cells
-plants can dilate these channels
-bridges the cell membranes and cell walls of adjacent cells
37
What is the function of desmosomes?
-attaches animal cells together without stopping flow of materials
-used to absorb mechanical stress by distributing throughout the tissue
38
what is the function of tight junctions? Where are they used?
-junctions b/w animal cells that block passage and leaks of materials
-holds cells together in actual physical contact
-Used in: stomach, capillaries, & bladder
39
What is the function of gap junctions?
-bridges space b/w animal cells (narrower than desmosomes)
-contains channels connecting cytoplasms of adjacent cells (allows communication)
-used in: pancreas (coordinated response of insulin), adn heart muscle cells (permit flow of ions to synchronize contractions)
40
Practice question 3: Is diffusion a spontaneous process?
YES
41
What is the end result of diffusion in a closed system?
Equilibrium of molecules on both sides (most cells do not want eqm because
42
What is net movement, net diffusion and dynamic eqm?
-Net movement: one direction - movement in other direction
-net diffusion: when the flow of solute particles is greater in one direction than the flow of solute particles in the other direction
-The cells operate to make sure that we don't deviate from a narrow range of internal balance (dynamic eqm, but not total eqm)
43
what are the 4 factors that affect the rate of diffusion of a substance?
concentration gradient, membrane permeability, temperature, and pressure.
44
What's the difference between simple and facilitated diffusion?
-simple: direct transport transport of molecules across plasma membrane (examples: water, oxygen, carbon dioxide, ethanol and urea)
-facilitated: requires a transmembrane protein (carrier, channel, or aquaporins) (examples: carbohydrates, amino acids, nucleosides, and ions)
45
What are transporters and what is their structure and function?
-Carrier and channel proteins
-carrier; binds to the substance to make it change shape and cross membrane
-channel; forms small pores in membrane allowing small molecules to pass
-structure: alpha-helical structures of the membrane-spanning domains
46
What is facilitated diffusion via channels? What are two examples?
-contain hydrophilic corridors that allow specific molecules to pass (no change in shape, but can have a gate)
-Examples: Aquaporins (facilitated diffusion of water), ion channels (open and close w/ stimulus)
47
What is facilitated diffusion via carrier proteins?
-Binds to a solute and undergoes a subtle change in shape upon binding to a solute that translocates the solute-binding site across the membrane
-examples: GLUT4 (transports glucose), LacY (transports lactose)
-rate depends on # of carriers
48
What is osmosis?
-The diffusion of water across a permeable membrane
-Goes from low to high due to cohesion and adhesion
49
What drives osmosis?
It's driven by impermeable solutes only
50
What is an osmotic gradient?
It is the difference in concentration between two solutions on either side of a semipermeable membrane (tonicity is the measure of the osmotic gradient)
51
What is osmotic pressure and how does it work?
-the hydrostatic pressure needed to stop the net flow of water across a membrane due to osmosis
-High solute concentration = high osmotic pressure
-Low solute concentration = low osmotic pressure --> this is important for keeping cells under homeostasis
52
Is osmosis spontaneous or non-spontaneous?
It is the spontaneous net movement
53
What is the end result of osmosis in a
closed system?
An equal concentration on both sides of the membrane
54
Does osmosis typically reach equilibrium in cells?
55
Define effective osmolarity
Osmolarity is the total concentration of all solutes
56
What is tonicity?
It is tonicity which is the ability to cause a cell to gain or lose water (effective osmolality)
57
Explain what happens to a cell in isotonic, hypertonic, and hypotonic solutions
-Isotonic: Same concentration inside and outside of cell and no net water movement. (normal)
-Hypertonic: solute concentration in solution is greater than inside the cell, and cell loses water making the cell shrivel
-Hypotonic: solute concentration in solution is smaller in solution than inside the cell and the cell gains water making it burst
58
Explain what determines whether a cell will gain or lose water by osmosis?
-Osmolarity is the total concentration of all solutes and it determines if the cell will gain or lose water.
-Iso-osmotic: particles of solute are the same on each side (cell does not gain or lose water)
-Hyper-osmotic: concentration of solutes is higher outside the cell so the cell loses water and becomes shriveled
-Hypo-osmotic: concentration of the solutes is greater inside the cell than outside so the cell gains water and bursts
59
What is turgor pressure? And how is it important in plants?
solution surrounding the cells is hypotonic so the vacuole becomes full providing pressure on the cell wall (makes plant stand up straight without it, the plant shrivels)
60
What is osmoregulation?
is the control of water balance
61
Why is osmoregulation important for some organisms (give examples (3))?
Examples:
1) Paramecium; is hypertonic to the pond water so it has a special organelle called the contractile vacuole which acts as a pump and pushes out water
2) urinary system
3)Plants; to help cell walls help maintain water balance (hypotonic, isotonic, & hypertonic)
62
What is active transport?
-Net movement is always against the gradient
-Cell must expend energy
-Transported molecules can be large or small
-Requires a carrier/transporter protein
-Allows cell to maintain different internal and external environments
63
Is active transport spontaneous or nonspontaneous?
If molecules have to be transporter from low to high the energy is expended and it is spontaneous
64
How does active transport differ from facilitated diffusion?
-Facilitated diffusion goes from high to low and doesn't require energy
WHEREAS
-active transport requires energy as molecules go from low to high
65
what unifies active transport and facilitated diffusion?
The both use carrier proteins to assist in the transport of molecules
66
What is the mechanism of a pump?
Pumps, also called transporters, are transmembrane proteins that actively move ions and/or solutes against a concentration/gradient
67
Does the mechanism of a pump more closely resemble a channel or a carrier?
channel
68
What is an electrogenic pump?
Ion pumps are electrogenic pumps. These pumps are transport
proteins that generate a voltage across a membrane
69
What is the main pump in animals? Other organisms?
The Na+/K+ ATPase is the main electrogenic pump of animal cells and
is especially important in neuronal physiology
70
What are some important functions of electrochemical gradients in cells and organisms?
1) an electrical gradient (different net charges inside and outside the cell)
2) A concentration gradient For example, more Na+ outside the cell makes the gradient go from outside (high) to the inside (low) of the cell.
71
Why are Na+, K+, H+ gradients important?
-They create membrane potential through active transport (i.e. positive exterior/negative interior) which favours the passive transport of cations(+) into the cell and anions(-) out of the cell by ion channels
-it drives processes like cellular respiration, transmission of nerve impulses and muscle contraction
72
What is secondary active transport?
-can produce electrochemical gradients that store energy for cellular work
-it is the use of an existing gradient to drive the active transport of a solute
73
What are some examples of secondary active transport in plants & animals
1) Plants; Plants use ATP to pump H+ against its gradient out of the cell and the H+ gradient is coupled transport sucrose into the cell
2) Humans; Glucose is co-transported into intestinal epithelial cells (where glucose concentration is high) with Na+ as it moves down the gradient created by the Na+/K+ pump
74
What are the differences in activities of a uniporter, a symporter and an antiporter?
1) Uniporter: A single solute moves in one direction
2) Symporter: Two solutes move in the same direction
3) Antiporter: Two solutes move in opposite directions
75
Can you describe the process of bulk transport?
-Large molecules (polysaccharides and proteins), viruses and bacteria must cross the membrane in bulk transport via vesicles
-They leave a cell by exocytosis; they enter a cell by endocytosis
-Requires energy
76
Compare constitutive vs. regulated bulk transport of exocytosis.
1) Constitutive: macromolecules are secreted from the cell without having to await a specific signal
2) Regulated: contents of a vacuole are secreted in response to a specific signal
77
What is exocytosis?
-Vesicle fuses with plasma membrane and releases contents into extracellular space
-proteins and phospholipids are incorporated into plasma membrane
78
Question: Are the following regulated or constitutive processes?
-Example 1: Insulin release by pancreatic cells (REGULATED)
-Example 2: Neurotransmitter release by neurons (REGULATED)
79
What is endocytosis? (3 types)
1) Phagocytosis: Large particles engulfed into vacuole which fuses with lysosome (ie. Bacteria are ingested by white blood cells)
2) Pinocytosis: Nonspecific uptake of extracellular fluid
3) Receptor-Mediated Endocytosis: Triggered by binding of ligand to surface receptor
80
What makes receptor-mediated endocytosis different?
-A vesicle is formed through recruitment of a coated pit when specific molecules attach to their specific receptors on the membrane
-This is a specific mechanism meaning it depends on the molecule it's taking in
-Cells take in LDLs via receptor-mediated endocytosis (they bind to specific surface receptors)
81
What is the purpose of cell-cell signaling in unicellular organisms? How is this achieved? What molecules are involved?
-It allows populations of cells to coordinate with one another and work like a team to accomplish tasks, this is called quorum sensing
-This is achieved when the concentration of an autoinducer reaches a certain level due to population density and the bacteria coordinate a response
82
What are examples of specific responses to cell-signaling in unicellular organisms (5)?
1) Sporulation (protists & bacteria) by quorum sensing
2) Exchange of plasmid DNA
3) Bioluminescence
4) Virulence: Secretion of proteins (help cause disease in multicellular organisms)
5) Production of biofilms: hard, polysaccharide-rich substances that encase the cells and attach them to a surface.
83
What are examples of molecules used in cell signaling in multicellular organisms?
-Happens (most often) through the release of chemical messengers
-Pheromones; Male luna moths detect pheromones with their antennae
-volatile compounds released by plants when under attack can attract another organism to help (caterpillar and parasitoid wasp)
84
What are the four types of local cell-signaling?
1) through cell junctions
2) cell surface molecules
3) paracrine signalling
4) synaptic signalling (neurotransmitters)
85
How do we communicate through cell junction?
-through the transfer of molecules through these junctions
-this is done through gap junctions between animal cells and between plasmodesmata between plant cells.
86
How do we communicate through cell surface molecules?
-GPCRs and RTKs are cell surfcace receptors.
- when a signal molecule binds to a cell surface molecule is changes the proteins shape which causes a change in the cells activity
87
How do we communicate through paracrine signalling?
A secretory cell releases local regulator molecules (with secretory vesicles) that travel through the extracellular matrix to nearby cells
88
How do we communicate through synaptic signalling?
-Neurons communicating with the release of neurotransmitters
-They act as chemical messengers diffusing across the synapse (the functional junction between the nerve cell and its target cell)
-has an effect on nearby neurons or effector organs such as muscles or glands
89
What is the type of cell-cell communication involved in long-distance cell-signaling? Describe it and give 2 examples
-Endocrine (hormones)
-activities in organs and tissues are regulated by hormones
-only have an effect on cells that have specific receptors (target cells)
-Examples: Insulin --> stimulates glucose uptake in animal bloodstream, Thyroxine --> regulates metabolism in animals
90
What are the stages of cell signalling?
A) Reception;
B) Transduction
C) Response
D) Signal deactivation
91
Describe A) Reception in cell signalling
-signalling molecule (ie. a hormone) binds to a receptor protein located at the target cell’s surface or inside the cell
-Binding causes the receptor protein to change shape and activate letting it interact with molecules in the cytoplasm
92
What are the two types of signalling molecules used in reception?
1) Water soluble; amino acid based, hydrophilic, can't diffuse through PMs (plasma membranes) of target cells so they bind on the surface of the cell (cell surface receptor-mediated signalling)
2) Lipid soluble; steroid and thyroid hormones, hydrophobic, can diffuse through PMs of target cells and bind to receptors in cytoplasm or nucleus (Lipid soluble signalling molecules)
93
What do extracellular receptors (cell surface receptors) do?
-signalling molecules (water soluble) bind to their receptors and the receptor proteins change shape
-they perform enzymatic function, allow passage of molecules (in and out) and initiate a transduction pathway
-examples: insulin and glucagon
94
What do intracellular receptors do?
-lipid soluble signalling molecule passes through membrane and they bind to a specific receptor in the cytoplasm or nucleus
-they alter gene expression meaning up-regulated (more proteins) or down-regulated (less proteins made), they also activate transcription factors
-examples: hormones like testosterone
95
What are two main types of membrane receptors?
1) G protein-coupled receptors (GPCRs)
2) Receptor tyrosine kinases
96
What is the main difference between GPCRs and RTKs?
RTKs have the ability to initiate multiple signalling cascades from a single
ligand-binding event (this is the main difference between GPCRs and RTKs)
97
What are some functions that GPCRs do?
-Some functions include; Embryonic development, Sensory reception (smell, light, taste, pheromones, etc.), Autonomic nervous system
transmission, and Mood regulation
98
What do G-proteins do? What do they hydrolyze?
-G proteins are peripheral membrane proteins that act as an on/off switch depending on if GTP or GDP is bound to them.
GDP: inactive
GTP: active
-G proteins are GTPase enzymes. They hydrolyze their GTP to GDP,
which inactivates themselves along with the targeted enzyme.
99
What does dimerization mean? And what does it do RTKs?
-a general mechanism to increase binding site affinity, specificity, and diversity
-When the signalling molecules bind to the active site of a monomer, they gain higher affinity for each other and the monomer RTKs bound to a ligand bind to each other (2 monomers attached = dimer complex)
-And this dimerization activates the tyrosine kinase region of each monomer
100
Describe B) Transduction in cell signalling.
This stage converts the signal from reception to a form that can bring about a specific cellular response this often requires a sequence of series in a series molecules (relay (effector) molecules) - a signal transduction pathway
101
Define a second messenger and discuss how these are involved in cell signaling?
molecules that relay signals received at receptors on the cell surface — such as the arrival of protein hormones, growth factors, etc. — to target molecules in the cytosol and/or nucleus
102
What are the 2 second messengers and how can their concentrations in the cytosol build up during cell signaling?
-Ca2+: higher concentration in smooth ER and in mitochondria than in cytosol and they are released in cytosol with the reception of chemical messengers; they are the main second messenger in muscle contraction
-cAMP: made by removing 2 phosphates from ATP by an enzyme called adenylyl cyclase. Signaling cascades permit boosting the normal cellular [cAMP] by 20-fold in seconds. cAMP broadcasts the signal to the cytoplasm, but it does not persist for long because another enzyme converts cAMP to AMP inactivating the signal
103
What is a phosphorylation cascade and how are these are involved in cell signaling?
Phosphorylation involves the transfer of the terminal phosphate
group from ATP to a protein molecule this activates the protein and causes a conformational change and it's a mechanism used for regulating protein activity
104
What is the term used for enzymes that can phosphorylate other proteins?
Kinase is an enzyme that phosphorylates proteins
105
What is signal amplification and why it is possible during signal transduction?
Signal amplification is a pathway in which one molecule activates which results in more molecules activating and this is possible because of the phosphorylation cascade during transduction
106
What are main molecular mechanisms for how a cell changes its activity in response to a signal?
-Catalysis by an enzyme
-Rearrangement of the cytoskeleton
-Activation of specific genes in the nucleus
107
Describe C) Response in cell signalling.
-the transduced signals trigger a specific cellular response, some of these include Catalysis by an enzyme, Rearrangement of the cytoskeleton, and Activation of specific genes in the nucleus
-response depends on the receptors/molecules involved in the cascade within the target cell
108
Which of these responses would be considered a nuclear response? Cytoplasmic response? Which one takes longer?
-Nuclear (change in which genes are expressed - slow):
-->Catalysis by an enzyme & Rearrangement of the cytoskeleton
-Cytoplasmic (Activate/deactivate target protein already in cell - FAST):
-->Activation of specific genes in the nucleus
-Nuclear takes longer
109
Describe D) Signalling deactivation in cell signalling.
-have automatic and rapid mechanisms for signal deactivation that allow the cell to remain sensitive to stimulus
-Can be deactivated if: signal is no longer produce, removal from receptors, or protein deactivation
110
Describe how signaling pathways form signaling webs. Describe pathway branching and pathway crosstalk.
111
How does one signaling molecule have different effects on different cell types and lead to different effects in different organs?
Because the response to a signaling molecule will depend upon the type of receptor and/or molecules involved in the cascade within the target cell.
112
Can you name specific examples of when cell-signaling is abnormal?
-It's implicated in various human disorders and diseases such as cancer
-abnormal cell signalling in cell division can lead to cancer and there are 2 possible ways;
a) positive regulators (kinases) of the cell cycle may be overactivated
b) while negative regulators, also called tumor suppressors (like
p53), may be inactivated
113
Can you compare aerobic cellular respiration, anaerobic cellular respiration, and fermentation in terms of the use of an electron transport chain and oxygen?
-Aerobic cellular respiration: Contains ETC during last stage oxidative phosphorylation that contains oxygen at the end driving the proton gradient with electronegativity.
-Anaerobic cellular respiration: Contains an ETC, but the final acceptor is NOT oxygen, it is nitrite, nitrate, CO2, etc.
-Fermentation: NO ETC
114
Which of those three metabolic processes generate ATP? Which one is most efficient? Which ones do not consume oxygen?
-All three pathways produce ATP, but aerobic cellular respiration is the most efficient as it produces the most ATP per glucose molecule
-Both fermentation and anaerobic cellular respiration do not require oxygen
115
What are the two main types of fermentation and how do they differ from each other?
-Alcohol Fermentation:
Produces ethanol and organic acids; this is performed by many bacteria under anaerobic conditions
-Lactic Acid Fermentation:
Produces lactate; this is performed by certain fungi, some bacteria and animals under anaerobic conditions.
116
Is the generation of ATP restricted to having glucose as the reactant?
No, ATP can be made by breaking down carbohydrates, lipids and proteins
117
What is a redox reaction and why are redox reactions coupled?
-A redox reaction involves the transfer of electrons which produces a reduced product and an oxidized product.
-Oxidation: the loss of electrons by a less electronegative molecule
-And this reaction is coupled because electrons cannot exist in a free state in cells
118
Describe what happens when a molecule is reduced. Describe what happens when a molecule is oxidized.
-A molecule is reduced when it gains electrons which are transferred over by a reducing agent
-A molecule is oxidized when it loses electrons (gives up energy) and this is caused by an oxidizing agent
119
Define a reducing agent, oxidizing agent, electron donor, and electron acceptor.
-Reducing agent: reduces another molecule by donating their electrons to them
-Oxidizing agent: oxidizes other molecules by accepting electrons from them
-electron donor: releases electrons
-electron acceptor: accepts electrons from the donor
120
What are the oxidized and reduced molecules in cellular respiration?
-Reducing agent: C6H12O6
-Oxidized agent: O2
-Reduced: H2O
-Oxidized: CO2
121
What are dehydrogenases? What molecule is its coenzyme?
-Dehydrogenases are oxidoreductase enzymes; they catalyze the oxidation of a substrate through the transfer of hydrogen
-NAD+ is the coenzyme to dehydrogenases (coenzymes bond to the active sites of enzymes and assists them)
122
Compare NAD+ to NADH and FAD to FADH2.
-NAD+ is oxidized form
-NADH is reduced form
-FAD is oxidized form
-FADH2 is reduced form
123
What is the importance of NADH and FADH2 holding an intermediate position in the overall spectrum of reducing power in the cell?
-It's important because when H2 and O2 are combined and EA is provided it will have an explosive reaction so to prevent this, NADH and FADH slowly release the electrons into an ETC which removes some of the energy making it possible to harness the energy safely
124
What are three important energy carriers produced in catabolic pathways in energy metabolism?
1) ATP
2) FADH2
3) NADH
4) NADPH
125
What happens to the energy of a phosphorylated molecule?
Energy is increased as the transfer of a phosphate group also transfers the energy (like ADP to ATP)
126
What's the importance of ATP holding an intermediate position in the overall spectrum of energy-rich phosphorylated compounds in the cell?
-ATP has a high phosphorylation potential making it easy to donate phosphate groups which also transfers energy
127
What are the structural components of a mitochondrion? (Identify the inner and outer membrane, intermembrane space, cristae, and matrix.) How many membranes does it have? What do these membranes contain? Where does oxidative phosphorylation occur? Where do protons (H+) accumulate?
-(DRAW IT)
-It has 2 membranes; the outer membrane and the inner membrane
-The inner membrane is used in cellular respiration; it is the site of
electron transport and chemiosmosis
-Oxidative phosphorylation happens in the inner membrane
-Protons accumulate in the intermembrane space while they move through the ETC
127
Can you briefly describe how energy is harvested by oxidative phosphorylation? Mention: electron carriers, electron transport chain (ETC), electrochemical gradient, ATP synthase
There's a chain of electron carriers and 4 protein complexes that make up the ETC, and because oxygen is the final acceptor it creates an electrochemical gradient that causes the protons to flow down the chain and to the most electronegative O2 atom. At the end of this gradient, the protons are transferred to an enzyme called ATP synthase where it uses the energy from the gradient to power the synthesis of ATP
128
Why does aerobic cellular respiration need an ETC? What would happen if hydrogen and electrons were directly transferred to oxygen without an ETC?
An explosive reaction would occur because the direct combination of H2 and O2 (once the EA is satisfied) combine explosively. The ETC provides a controlled way to release energy to be harvested for the synthesis of ATP
129
List the 4 steps of cellular respiration and indicate where each occurs in a eukaryotic cell.
1) Glycolysis - Cytoplasm
2) Pyruvate Oxidation - Mitochondrial matrix
3) Citric acid cycle (Krebs) - Mitochondrial matrix
4) Oxidative Phosphorylation (ETC) -Mitochondrial matrix
130
Why is the regulation of glucose oxidation important? and what are some types of regulation used to control glucose oxidation (describe)?
-It’s important that glucose oxidation is regulated because it maintains a certain level of glucose in our blood, the rate at which glucose is consumed is regulated, and the process will be shut down when too much ATP is created meaning too much glucose was used
-PFK (phosphofructokinase) and Hexokinase both regulate glucose oxidation (AMP activates, ATP and citrate deactivate)
131
What are the chemical ratios that can be used by a cell to monitor energy levels and regulate glycolysis and cellular respiration?
-ATP : too much acts a stop signal
-ADP
-NADH
132
What are 3 characteristics of phosphofructokinase that make it a good target to regulate glycolysis and cellular respiration?
1) inhibition and activation is tightly controlled by citrate, ATP (inhibition) and AMP (activation)
2) When inhibited it stops the process of cellular respiration
3) it can influence the rate of glucose consumption by regulating glucose 6-phosphate
133
How is phosphofructokinase regulated by ATP and what kind of regulation is involved?
-PFK is regulated when the levels of ATP or citrate become elevated, PFK becomes inhibited, and when the levels of ATP and citrate drop and the levels of AMP increase, AMP allosterically activates PFK
-The type involved = allosteric regulation (binds to the enzyme not on the active site and changes its conformation)
134
Which 2 major components make up oxidative phosphorylation? Where are they found in the mitochondria and what are their functions?
1) The ETC; Found in the mitochondrial membrane + it oxidizes NADH & FADH2 and use these protons to create a gradient (in the inter-membrane space)
2) ATP Synthase; Found in the mitochondrial membrane + it harnesses the energy provided by the protein gradient and uses it to power the synthesis of ATP (mitochondrial matrix)
135
Why is the process of making ATP referred to as oxidative phosphorylation?
It’s because this process relies on a series of oxidative reactions to transfer electrons which can then be harnessed to add a phosphate group to ADP to form ATP
136
What are the major components of the mitochondrial ETC, what are their functions and what are their associations with the membrane?
Major components:
1) Proteins that form 4 multi-protein complexes; complexes 1,3,4 are proton pumps that create a gradient across the inter-membrane space
2) ATP synthase; a multi-subunit complex w/ 4 parts; rotor - spins when H+ flow by, stator- holds stationary knob, rod- extends into knob and activates catalytic sites in knob, three catalytic sites- join inorganic phosphate to ADP to make ATP. It uses the energy from the proton gradient to power the synthesis of ATP
137
What is a terminal electron acceptor and what is the final electron acceptor in aerobic and what are some examples in anaerobic?
-It is the last compound to receive an electron in an ETC
-aerobic: O2 (very electronegative)
-in aerobic: nitrite, nitrate, CO2, metal ions, sulfate, etc.
138
Why is the stepwise transfer of electrons to the next electron acceptor in the chain important for the overall function of the ETC and how is this accomplished?
It’s important because it releases energy creating a gradient which can be harnessed and used to synthesize ATP, and it is accomplished as the electron carriers alternate between reduced and oxidized states as they accept and donate electrons.
139
Where do the electrons from NADH and FADH2 enter the ETC? (Trace the pathway of these electrons)
-NADH: enters the ETC at complex I, 1st electron acceptor is flavoprotein and last electron acceptor is coenzyme Q. The rest of the electron carriers are called cytochromes, the last cytochrome (Cyt a3) passes electrons to O2 which is the final electron acceptor.
-FADH2: enters ETC at complex II, 1st electron acceptor is Fe-S and last electron acceptor is coenzyme Q. The rest of the electron carriers are called cytochromes, the last cytochrome (Cyt a3) passes electrons to O2 which is the final electron acceptor.
140
Which electron carrier, NADH or FADH2, contributes the most to the H+ concentration gradient when it donates electrons to the ETC and why do the contribute the most?
NADH contributes the most H+ (each NADH results in 10 H+) and this is because NADH enters the ETC at complex I meaning it will go through more coupled reactions than FADH2 which enters at complex II.
141
What are the two major structural components of ATP synthase joined by a stator and rotor? And what are their functions?
1) A rod: extends into the knob also spins, and activates the catalytic sites in the knob
2) The knob: The rotation of the knob causes conformational changes and activates its 3 catalytic sites that join ADP with Pi to make ATP
142
Describe the energy conversions in the process of cellular respiration. (how much ATP per electron carrier?)
1)NADH = 2.5-3.5 ATP = 3 ATP
2)FADH = 1.5 ATP = 2 ATP
143
How are the activities of the ETC and ATP synthase coupled and what would happen if one of them stopped working?
-The ETC provides the energy (proton gradient) possible to form ATP in the ATP synthase.
-If the ETC were to stop, oxidative phosphorylation would not occur.
-If ATP synthase stopped working, the proton gradient would become backed up and the ETC would cease to function.
144
What's the number of ATP molecules made by cellular respiration per molecule of glucose? And why does it vary for each cell?
-Between 36-38 molecules of ATP
-This number varies depending on the type of shuttle (cells use different shuttles) used to transport the 2 NADH made in glycolysis; glycerol 3-P shuttle uses 2 ATP (results in 4ATP) to transport whereas Malate-Aspartate (results in 6ATP) doesn't use any
145
How much ATP is made during glycolysis?
-4 ATP made
-2 ATP is consumed
146
How much ATP is made during Pyruvate oxidation?
-0 ATP made
147
How much ATP is made during the krebs cycle?
-2 ATP made
148
How much ATP is made during oxidative phosphorylation?
-34 ATP made
149
What is the efficiency of aerobic cellular respiration and why is it not 100%?
-40-42% efficient
-It's so low because everything else is lost as heat
150
How many H+ per ATP is used in cellular respiration?
5/2 H+ or 2.5 H+ per ATP molecule
151
What's the balanced equation for cellular respiration, is it endergonic or exergonic, and is carbon in glucose oxidized or reduced?
C6H12O6 + 6O2 + ADP + Pi --> 6CO2 + 6H2O + energy
-It's exergonic with a G = -2870kJ/mol
-Carbon in glucose is oxidized
152
Which organisms can undergo ATP synthesis in the absence of oxygen?
-Obligate anaerobes; such as certain archaea and bacteria. Oxygen is toxic to them
-Facultative anaerobes; such as Yeasts and bacteria can undergo ATP synthesis with or without oxygen
153
Describe each step of anaerobic cellular respiration (3 steps). Does it have an ETC and what is the final acceptor?
1) Sugars are oxidized producing NADH which carries electrons to the ETC in the mitochondria
2) ETC (shorter); NADH and FADH2 are oxidized to create a proton gradient in the ETC (final acceptor = nitrite, nitrate, sulfate, CO2, metal ions, etc.)
3) ATP synthesized through chemiosmosis w/ the H+ gradient
154
What's the goal of fermentation and what does it do?
-It's a way of harvesting chemical energy without oxygen and ETC.
-In this process Pyruvate is incompletely broken down and NAD+ is recycled
155
Describe alcohol fermentation (2 steps). How much ATP is made?
-Pyruvate is converted into ethanol:
1) CO2 is released making pyruvate into acetaldehyde.
2) Then acetaldehyde is reduced by NADH to ethanol resulting in NAD+ (NAD+ cycle)
- 2 ATP is made
156
Describe lactic acid fermentation and how does it defer from alcohol fermentation?
-Pyruvate is directly converted to lactate, regenerating NAD+
-NO release of CO2
157
Does fermentation require oxygen?
NO
158
Which organisms use alcohol fermentation?
Yeast and bacteria
159
Which organisms use lactic acid fermentation?
Certain fungi and bacteria
160
Why is lactic acid fermentation important for our muscle cells?
-They make ATP by alcohol fermentation during strenuous exercise as oxygen becomes sparse
161
Rank aerobic cellular respiration, anaerobic cellular respiration, and fermentation on how much ATP they produce per glucose and explain why.
1) aerobic cellular respiration (because it as a longer ETC than anaerobic and the molecule at the end is more electronegative meaning it can create a bigger proton gradient)
2) anaerobic cellular respiration (because of its final electron acceptor not being oxygen)
3) fermentation (NO ETC)
162
What are the two other groups of organic molecules that can feed into cellular respiration and which of the 3 that are used are better and why?
-Proteins and lipids as fuel:
-Lipids are used first and yield more ATP than both carbs and proteins
1)lipids
2)carbs
3)proteins
163
Which major step do monosaccharides (other than glucose), disaccharides and polysaccharides enter cellular respiration?
-monosaccharides and disaccharides: when they're in excess they're turned into glycogen and other long term fat storage (liver/adipose cells)
-polysaccharides: starch and glycogen enter at glycolysis; the breakdown of glycogen is called glycogenolysis
164
Describe the breakdown of fats. Mention lipases, beta-oxidation, and the organelles involved in the process. Indicate at which major steps the glycerol and acetyl CoA generated enter cellular respiration.
-Glycerol is converted in glycerol 3-P and enters glycolysis. Lipase is an enzyme that breaks down fat. Fatty acids are broken down through beta oxidation into Acetate generating NADH and FADH2. Each acetate unit enters at pyruvate oxidation attaching themselves to acetyl coA and then enters the krebs cycle through substrate level phosphorylation
165
Briefly describe the breakdown of proteins. Mention proteases/peptidases and deamination. Indicate at which step (major steps) the deaminated amino acids enter cellular respiration. Briefly describe how the excess amino groups are eliminated from the body in vertebrates.
-Proteins are broken down by protease enzymes into constituent amino acids then their amino groups are removed through deamination. The organic acids are then converted into intermediates in cellular respiration depending on the amino acid it derives from amd will enter either at glycolysis, pyruvate oxidation or the krebs cycle.
-the toxic amino groups are converted into urea and is excreted
166
How can intermediates in cellular respiration be used in biosynthesis (anabolic) pathways? Give examples of molecules produced from glucose, pyruvate, intermediates of glycolysis, acetyl CoA, and intermediates of the citric acid cycle.
-Ingested carbohydrates, proteins, and fats are not always catabolized they're often used to create macromolecules (anabolic and consumes ATP)
EXAMPLES:
-11 of the amino acids in some proteins come modifying compounds diverted from krebs cycle
-glucose can be made from pyruvate and fatty acids from acetyl CoA
-intermediate compound generated during glycolysis,
dihydroxyacetone phosphate (DHP), can be converted to one of the major precursors of fats
167
What are the energy sources and carbon sources in chemoautotrophs, photoheterotrophs and photoautotrophs?
-chemoautotrophs: energy = chemical compounds; carbon = CO2
-photoheterotrophs: energy = light; carbon = organic compounds
-photoautotrophs: energy = light; carbon = CO2
168
What are four different groups of organisms that are photoautotrophs?
plants, algae (protists), cyanobacteria, purple and green
sulfur bacteria
169
What are the ecological roles of primary producers?
-they convert solar energy into chemical energy that can be used by other organisms; they are the first level of the food chain so they provide energy to the rest of the food web
-Photoautotrophs and chemoautotrophs = primary producers
170
What is the balanced equation for the process of oxygenic photosynthesis?
light + 6 CO2 + 6 H20 = C6H12O6
(sugar) + 6 O2
171
how do cellular respiration and photosynthesis contribute to the carbon cycle?
-cellular respiration releases carbon dioxide into the environment, photosynthesis pulls carbon dioxide out of the atmosphere
172
What's the balanced equation for Anoxygenic photosynthesis?
light+ 6 CO2 + 6 H2S = C6H12O6 (sugar) + 6 S
173
which of the four photoautotroph groups perform oxygenic photosynthesis and which perform anoxygenic photosynthesis?
1) Plants = Oxygenic photosynthesis
2) Algae = Oxygenic photosynthesis
3) Cyanobacteria = Oxygenic photosynthesis
4) anaerobic green and purple sulfur bacteria = Anoxygenic photosynthesis
174
How do these plants structures: vascular tissue, stomata, and mesophyll aid in photosynthesis?
1) vascular tissue: system of vessels to distribute substances
throughout a plant (H20, CO2, O2, sugar, minerals)
2) stomata: gas exchanges, essential for cellular respiration and photosynthesis happen through pores called the stomata
3) mesophyll: contain high amounts of chloroplasts that perform photosynthesis
175
Can you describe the general structure of a chloroplast? Mention inner and outer membrane, intermembrane space, thylakoids, grana, and stroma. Indicate the larger group of organelles in eukaryotes a chloroplast belongs to
LOOK AT A PICTURE GURL (RIGHT NEOW)
176
What is a pigment? What is the absorption spectrum and absorption of a pigment?
-Pigment: is a substance that
absorbs light energy and use it to to produce sugar (for plants, this is chlorophyll)
-Absorption spectrum: the wavelengths of light that a pigment is able to take in and use for photosynthesis
177
what colours do chlorophyll a and b absorb?
-chlorophyll a: violet and orange
-chlorophyll b: blue and yellow
178
What are the larger group of organelles in eukaryotes a chloroplast belongs to?
mesophyll
179
What is the family of photosynthetic pigments that act as the primary pigments in oxygenic photoautotrophs?
Chlorophyll a and b
180
What is the general structure of this family of pigments (chlorophyll)? Link each of the 2 major structural components of these molecules to a function
1) Porphyrin ring: magnesium center "head" that absorbs light
2) Hydrocarbon tail: serves to
stabilize the pigment in the
thylakoid membrane
181
What is another major group of photosynthetic pigments that also act as pigments in oxygenic
photoautotrophs? What are 2 functions of this pigment group?
-Carotenoids:
1) Colouration: they give leaves and fruits their yellow-orange colour by breaking down chlorophyll in response to cold temps
2) Photoprotection: absorb and dissipate excess light to prevent damage to chlorophyll and they prevent the formation of free radicals that could harm the cell
182
What happens when a pigment absorbs a photon and its energy is transferred to an
electron? Compare this event when the photon is blue light compared to red light.
-the electron gets excited and jumps to a higher energy level
-Only a photon with the exact amount of energy between the ground state and excited state can be absorbed this shows the specificity of certain pigment molecules for certain wavelengths
183
What are the 2 possible outcomes for an electron when it is excited to a higher energy level in a pigment?
1) if chlorophyll molecule is isolated:
- electron drops back down and absorbed light is emitted as heat, vibration or energy
2) Not isolated:
- The electrons are excited in series until they reach a reaction center: inductive resonance. Vibration energy is then transferred from one pigment to another until it reaches a rx center.
184
What are the 2 possible outcomes for the energy of an excited electron as the electron returns to its ground state?
can be emitted as heat or light?
185
What are the two major components of a photosystem (PS)? Describe the structure of
each component (EDIT THIS ONE TO ADD MORE DETAIL PAGE 7)
1) light harvesting complexes:
-contain pigment molecules
(antennae) which surround the
reaction center complex.
2) a reaction center complex:
-contains a specialized pair of
chlorophyll a pigments.
186
What are the functions of the 2 components of the photosystems in the light reactions?
1)light harvesting complex:
-when the pigments get excited an electron gains energy and
transfers it through inductive
resonance to a neighboring pigment
2)reaction center:
-energy is transferred and reaches the reaction center where a special pair of chlorophyll a transfer an excited electron to the primary electron acceptor
187
What is the electron donor for each photosystem and how oxygen is produced as a byproduct in oxygenic
photosynthesis?
1)photosystem ii: Pheophytin (P680)
2)photosystem i: Chlorophyll A0 (P700)
-PS II: when P680 electron acceptor is in an excited state it is left with an oxidized pair of chlorophyll a molecules leading to water splitting to replace the electrons, O2 is made, H+ is released into the thylakoid and finally chlorophyll a takes one electron at a time and remain in the rx center
188
what is the byproduct produced when H2S is used as an electron donor instead of water in anoxygenic photosynthesis?
sulphur
189
What are the 2 sets of linked reactions in oxygenic photosynthesis and indicate where in the chloroplast they occur?
1) light-dependent reactions, which take place in the thylakoids
2) light-independent reactions (dark reactions or the Calvin cycle), which take place in the stroma
190
where are the PSs found in the chloroplast and in photosynthetic bacteria?
-Both photosystem II (PS II) and photosystem I (PS I) are in the thylakoid membrane
-AND in the cytoplasmic membrane of photosynthetic bacteria
191
Compare energy transfer vs. electron transfer in a PS.
-PSs differ in their reaction centers (this difference is caused by the protein associated with the chlorophyll a)
-PS II: has rx center called P680 because it's chlorophyll a has optimal absorbance at wavelength 680nm
-PS I: has rx center called P700 because it's chlorophyll a has optimal absorbance at wavelength 700nm
192
What is PS IIs function in the overall process of the light-capturing reactions? What are the molecules involved in the transfer of electrons in the order that they become reduced (transfer of electrons)? What is the molecule that replaces electrons in the reaction center by transferring them (becoming oxidized)?
-when P680 electron acceptor is in an excited state it is left with an oxidized pair of chlorophyll a molecules leading to water splitting to replace the electrons, O2 is made, H+ is released into the thylakoid and finally chlorophyll a takes one electron at a time and remain in the rx center.
-ETC: Made up of Plastoquinone (Pq), A series of cytochromes (Cyt), this stage creates a H+ gradient, Plastocyanin (Pc), P700 in PS I
-water replaces electrons
193
What is PS Is function in the overall process of the light-capturing reactions? What are the molecules involved in the transfer of electrons in the order that they become reduced (transfer of electrons)? What is the molecule that replaces electrons in the reaction center by transferring them (becoming oxidized)?
-light energy has been transferred via light-harvesting complex pigments
to the PS I reaction center, exciting an electron of the P700 (pair of chlorophyll a molecules)
-Ferredoxin accepts H+ and transfers to NADP+ giving NADPH (catalyzed by NADPH reductase)
-NO ATP MADE
-electrons from PS II ETC go to P700 to go back to original reduced state
194
Describe the reaction carried out by the oxygen evolving complex of PSII and its importance in the overall process of the light-capturing reactions
Through the water-splitting reaction of PSII, light energy is converted into biologically useful chemical energy, and molecular oxygen is formed which transformed the atmosphere into an aerobic one
195
Explain how a H+ electrochemical gradient (proton motive force) is involved in the light reactions. Indicate where the gradient is generated. List three processes that contribute to the gradient.
-ETC1 creates a proton
gradient in the thylakoid
membrane which drives chemiosmosis & synthesizes
ATP.
-and the electrons from the ETC are passed to P700 which brings them back to their reduced state
196
why is photosynthesis thought to be evolutionary related to cellular respiration? Mention the ETC and ATP synthase
Cyanobacteria released enough oxygen to facilitate the development of aerobic respiration (?)
197
Describe linear electron flow; when each occurs and what function it has in photosynthesis.
-PSII --> ETC 1 --> PSI --> ETC 2
-Makes both ATP & NADPH & O2
-PS II makes high energy electrons that are transferred to ETC 1. Resulting in a pair of oxidized chlorophyll that get reduced by an electron from water making O2. ETC 1 creates proton gradient which is used to power ATP synthesis. End of ETC 1, electrons transferred to PS I. The energy boosts their energy level which is used to make NADPH following ETC 2.
198
Describe cycle electron flow; when each occurs and what function it has in photosynthesis?
-Only makes ATP
-only uses PS I and short circuits
-transports electrons through the ETC1 and from there back to P700 in PS 1
-Ferredoxin (Fd) brings the electrons to the cytochrome complex of ETC1
199
Define carbon fixation & reduction
-carbon fixation: process where photosynthetic organisms turn inorganic carbon into organic compounds
-reduction: a reaction in which electrons are added to a compound
200
Briefly describe the diversity of pathways used to fix carbon in organisms.
Seven autotrophic carbon fixation pathways are known. The Calvin cycle fixes carbon in the chloroplasts of plants and algae, and in the cyanobacteria. It also fixes carbon in the anoxygenic photosynthesis
201
Indicate the group of organisms where most diversity exists. List the groups of organisms that use the Calvin cycle.
-prokaryotes are the most diverse as they encompass bacteria and archaea.
-Photosynthetic eukaryotes, prokaryotes, algae, cyanobacteria, etc.
202
What's the first phase of the calvin cycle and what does it accomplish?
Phase 1:
-carbon fixation; CO2 is attached to 5C sugar (RuBP), enzyme is Rubisco (most abundant protein in chloroplasts and oxygen is a direct competitor)
-6C is unstable and is split into 2 3-PGA
203
What's the second phase of the calvin cycle and what does it accomplish?
Phase 2; reduction:
-3-PGA is phosphorylated into 6C using ATP. NADH is oxidized to reduce 1,3-bisphosphoglycerate into G3P.
-Used 3 CO2, 6 ATP, and 6 NADPH
-Made 6 G3P (1 leaves)
204
What's the third phase of the calvin cycle and what does it accomplish?
Phase 3; Regeneration of the CO2 acceptor:
-each entering CO2 combines with a RuBP molecule to initiate the cycle
-3 ATP are used while a series of catalyzed reactions to convert 5 G3P into 3 molecules of RuBP
205
What is the reaction carried out by rubisco?
RuBP combines with entering CO2 initiating the cycle. Then in a series of catalyzed reactions 5 G3P into 3 molecules of RuBP to restart the cycle.
206
What is the 3-carbon sugar intermediate of the pathway that can feed out of the cycle to be used to produce other sugars by cells (e.g., glucose)?
-G3P:
-50% goes to cellular respiration
-used to synthesize all major organic molecules (large majority used for cellulose)
-excess converted into glucose and starch
207
State how many carbons are fixed and the number and type of energy carriers that are used per turn of the cycle. Indicate in which steps of the cycle the energy carriers are used. State how many turns would result in a net production of 1 G3P (3-carbon molecule).
-FOR 3 C02:
1) carbon fixation: 0 ATP and 0 NADPH used
2) Reduction: 6 ATP and 6 NADPH used
3) Regeneration of RuBP: 3 ATP and 0 NADPH used
-3 turns result in the production of 1 G3P molecule
208
Other than being used directly in cellular respiration by leaf cells, describe 2 fates of sugars
produced plants. Indicate what product is made and its function for the plant.
It can be converted into cellulose used to help the plant grow and it can be converted into starch which is used as storage.
209
Why is rubisco considered inefficient? Provide a possible explanation why this enzyme is non-specific.
O2 is a direct competitor for rubisco’s active site. When O2 increases and CO2 decreases rubisco interacts with O2; this initiates a pathway called photorespiration
210
What is the first reaction of photorespiration when O2 is used by rubisco instead of CO2 (C3)?
-Instead of creating two
molecules of 3-PGA, one 3-
PGA and a 2C molecule are
formed
211
Describe the steps of photorespiration in C4 plants (5)
1) Mesophyll cell; CO2 is added to PEP to form oxaloacetate (enzyme = PEP carboxylase)
2) oxaloacetate is converted to
malate and exported through plasmodesmata to bundle-sheath cells (bsc)
3) malate releases CO2 into bundle sheath cells (C3 pathway)
4) CO2 incorporated into organic molecules by rubisco in bsc and calvin cycle can start
5) Pyruvate is regenerated and exported back to mesophyll cells for conversion to PEP using ATP
212
Why is photorespiration considered inefficient?
-It loses up to 50% of fixed carbon (C3), wastes energy (happens when plants close their stomata)
213
Describe when photorespiration occurs in plants. AND What is the importance of the ratio of CO2 :
O2 in the chloroplast?
-Photorespiration occurs usually when there is a high concentration of oxygen which generally happens when plants close their stomata and can no longer take in CO2.
-It's important to help prevent photorespiration from occurring
214
Describe why the cellular conditions for photorespiration occur in plants that occupy hot and dry climates.
Because plants in hot and dry climates will close their stomata in order to conserve their water and prevent evaporation, however this leads to the plants no longer being able to take in CO2 and their O2 concentrations increase leading to interactions between rubisco and O2
215
Discuss the CAM pathway used by CAM plants as an adaptation to limit the effects of
photorespiration. Mention temporal separation, PEP carboxylase, 4-carbon organic acids
-separated into two pathways; C4 pathway occurs at night in mesophyll cells and C3 pathway occurs during the day in mesophyll cells
1) C4;
-stomata open, bringing in CO2 into the mesophyll which is being fixed into organic acids which are then stored in vacuoles until morning
2) C3:
-stomata are closed and light reactions supply ATP and NADPH to the Calvin cycle
-Co2 is released from the organic acids
216
what are the enzymes used in glycolysis, what steps are they used in and what is the reactant and product? (6)
1) glucose ---> glucose-6-phosphate (hexokinase)
3) fructose-6-phosphate --> 1,6-biphosphate (PFK)
6) 2G3P -->1,3-biphosphoglycerate (triose phosphate dehydrogenase)
7) 1,3-biphosphoglycerate --> 3-phosphoglycerate (phosphoglycerokinase)
10) phosphoenolpyruvate --> pyruvate (pyruvate kinase)
217
what enzyme is used to catalyze the reaction of adding co2 to phosphoenolpyruvate to make oxaloactete in the C4 pathway?
PEP Carboxylase
