Exam 3 Flashcards
(150 cards)
1
Q
What does it mean when it says phospholipids are amphipathic molecules?
A
they have hydrophobic and hydrophilic regions
2
Q
Phospholipids are similar to triglycerides in what way and how do they differ?
A
Phospholipids are a glycerol molecule and has fatty acid tails however one of the fatty acid tails is replaced with a hydrophilic head which is composed of a phosphate that can be changed to also have a choline. The fatty acid tails are often unsaturated meaning they have a double bond.
3
Q
What does a longer hydrocarbon or increased fatty acid length mean?
A
longer hydrocarbons means the membrane is more solid or gel like (viscous)
4
Q
Explain how phospholipids and various proteins move within the bilayer
A
they drift laterally within the leaflet of the membrane and rarely flip flop across the membrane to the opposite leaflet without an enzyme helping
5
Q
Explain how unsaturated fatty acids and saturated fatty acids effect membrane fluidity
A
Membranes that have a lot of unsaturated fatty acids are more fluid than membranes that have a lot of saturated fatty acids
6
Q
What happens when more double bonds are added to the fatty acids?
A
the membrane becomes more fluid
7
Q
What role does cholesterol play in membranes?
A
Cholesterol helps moderate the fluidity of membranes. At warm temperatures (37 C) cholesterol restrains movement of phospholipids. At cool temperatures it keeps fluidity by preventing tight packing.
8
Q
What role do glycolipids play in membranes?
A
Glycolipids have saccharides that are responsible for cell recognition and anchoring of cells
9
Q
Explain the transformation of micelles to a liposome
A
First phospholipids assemble into micelles which then form into lipid bilayers. After the lipid bilayer grow to a critical size it will close up into a liposome. This is where a sealed compartment is formed, and the hydrophobic tails are shielded from the water. Liposomes are only composed of lipids.
10
Q
Where are lipids synthesized?
A
Endoplasmic reticulum
11
Q
What does the rough ER do in relation to membranes?
A
the rough ER with its bound ribosomes makes the protein component of membranes
12
Q
What does the smooth ER do in relation to membranes?
A
smooth ER synthesizes the lipid component of the membrane
13
Q
There are four classes of lipoproteins Chylomicrons:
A
transport dietary lipids to adipose tissue
14
Q
There are four classes of lipoproteins: Very-low-density lipoproteins (VLDL)
A
transport triglycerides from hepatocytes to adipocytes
15
Q
There are four classes of lipoproteins: Low-density lipoproteins (LDLs)
A
carry about 75% of the total cholesterol in blood and deliver it to cells
16
Q
There are four classes of lipoproteins: High-density lipoproteins (HDLs)
A
remove excess cholesterol from body cells and the blood and transport it to the liver for excreation
17
Q
What class of lipid proteins is considered “good cholesterol” and which is considered “bad cholesterol”?
A
LDLs are considered “bad” cholesterol because the fatty deposits build up in your arteries. HDL are “good” cholesterol because it helps remove the bad cholesterol from the body by carrying it to the liver for excretion.
18
Q
Explain the process of phospholipid synthesis
A
Synthesis of phosphoglycerides begins at the cytosolic face of the smooth ER membrane. It begins by the covalent attachment of two fatty acids to glycerol which produces phosphatidic acid. Phosphatidic acid is catalyzed by acyl transferees. Newly synthesized phospholipids are added to the cytosolic side of the smooth ER membrane. Scramblase transfers them from one leaflet of the lipid bilayer to the other. It also randomizes the distribution of phospholipid types so both sides of the membrane are the same.
19
Q
Explain how flippase and floppase are involved in phospholipid asymmetry
A
When vesicles bud off the ER, the asymmetry and orientations of the proteins that are embedded in are already set but the phospholipids in each leaflet are still randomized. After merging of the vesicle with the Golgi body, flippase catalyzes the transfer of specific phospholipids to the cytosolic leaflet which creates an asymmetry in phospholipid distribution. Floppase catalyzes the opposite movement of the phospholipids (from the cytosolic leaflet to the inner leaflet).
20
Q
In phospholipid asymmetry what will the orientation of the leaflets be? and what are the roles of glycolipids and glycoproteins?
A
One leaflet will face the lumen of organelles or be exposed to the outside of the cell; the other will always face the cytosol. The cell surface has many glycolipids and glycoproteins which is important for cell-cell recognition and anchoring to the extracellular matrix.
21
Q
Carbohydrates on the cell
A
The cell surface is covered in carbohydrates and these carbohydrates come together to form glycocalyx.
22
Q
Explain how glycolipids relate to cell-cell recognition using the ABO blood grouping system.
A
Donor blood is compatible depending on the type of glycolipid present on the surface of red blood cells. All people synthesize the basic ABO blood typing antigen O. Type A and B are able to modify the antigen. Type AB are able to modify equal amounts of the antigen to be both A and B blood types. Type O make no modifications to the antigen. Antibodies of incompatible blood recipients will recognize antigens not found in their own blood.
23
Q
Describe the fluid mosaic model
A
the fluid mosaic model depicts membranes as fluid structures with a “mosaic” of various proteins and other macromolecules embedded in it.
24
Q
Describe Freeze-fracture
A
Freeze-fracture is a preparation technique that splits a membrane along the middle of the phospholipid bilayer and separates the leaflets.
25
What are peripheral proteins?
they are bound to the surface of the membrane
26
What are integral proteins and how does it relate to a-helices?
they penetrate the hydrophobic core and if they span the membrane they are called transmembrane proteins. The hydrophobic regions of an integral protein consist of one or more stretches of nonpolar amino acid residues which are coiled into a-helices.
27
How do cells recognize each other and how does this involve receptor proteins?
Cells recognize each other by binding to surface molecules that contain carbohydrates (glycolipids and glycoproteins). Receptor proteins are important in cell recognition and response to stimuli.
28
How do cells attach to the extracellular matrix?
through a combination of receptor proteins and glycoproteins
29
What is protein's relationship to the attachment to the cytoskeleton and ECM?
Proteins anchor cells together and anchor their cytoskeleton components to the plasma membrane.
30
How are integrins involved in attachment to the cytoskeleton and ECM?
Integrins attach to the ECM and use intracellular signaling to report their state of attachment to the rest of the cell.
31
How do small molecules and water leave/enter the cell?
through the lipid bilayer or via transport proteins
32
How do large molecules like polysaccharides and proteins cross the membrane?
They cross the membrane in bulk via vesicles. Bulk transport across the plasma membrane occurs by exocytosis and endocytosis.
33
What happens in exocytosis?
transport vesicles migrate to the membrane, fuse with it and release their contents. Secretory cells use exocytosis to export their products. in order for vesicles to move around the cell and to the plasma membrane, energy must be expended to drive motor proteins down the cytoskeleton with the vesicle in tow.
34
What happens in endocytosis?
the cell takes in macromolecules by forming vesicles from the plasma membrane. reversal of exocytosis and involves different proteins. energy must be expended to form vesicles and transport them to appropriate regions of the cell.
35
What is phagocytosis?
A form of endocytosis "cellular eating". A cell engulfs a particle in a vacuole; the vacuole fuses with a lysosome to digest the particle
36
What is pinocytosis?
a form of endocytosis "cellular drinking". molecules are taken up when extracellular fluid is "gulped" into tiny vesicles
37
What is receptor-mediated endocytosis?
binding of ligands to receptors triggers vesicle formation. a ligand is any molecule that binds specifically to a receptor site of another molecule.
38
What is a plasma membrane?
A plasma membrane is a selectively permeable barrier that controls which agents enter and exit the cell by expressing different membrane transport proteins.
39
What is simple diffusion and what molecules are involved in this?
Simple diffusion is when small non-polar molecules can easily diffuse across the lipid bilayer without aid. Examples of this are O2, CO2, N2, steroid hormones
40
What molecules cannot go through the lipid bilayer and why?
Ions cannot go through the lipid bilayer because they have charges, and these charges can become attracted and stop in between the lipid bilayer since it's negative inside or they can turn back.
41
What is passive transport?
Proteins that act as channels or carriers that help specific agents diffuse across the membrane. Transport proteins provide a path for the passive movement of ions or molecules across the plasma membrane.
42
What is active transport?
Active transport is when proteins use energy to pump specific agents into the cell against their concentration gradient
43
What is diffusion?
Diffusion is the tendency of molecules to spread out evenly into the available space
44
What does equilibrium mean in terms of membranes.
the same amount of molecules cross the membrane in one direction as in the other, no net change in products and reactants
45
What direction do substances diffuse down their concentration gradient?
from high concentration to low concentration
46
Does work need to be done to move substances down the gradient?
no work needs to be done to move substances down the concentration gradient, but work can be extracted from these molecules.
47
What are channels?
Channels are membrane proteins that allow the direct passage through the membrane. They are specific for the type of ion or molecule that moves through them.
48
What are transporters or carrier proteins?
they are proteins that allow diffusion by binding substances which creates a change in the protein's shape that releases the substance on the other side of the membrane. These proteins are highly selective.
49
What are aquaporins?
Aquaporins are channels that allow water to move across the membrane and will not let other substances through. Almost all water that passes through a cell most go through these.
50
What is osmosis?
diffusion of water across a selectively permeable membrane
51
What way does water diffuse across a membrane?
From regions of lower solute concentration to regions of higher solute concentrations until the solute concentration is equal on both sides.
52
What is tonicity?
the ability of a surrounding solution to cause a cell to gain or lose water
53
what can cause osmotic pressure?
differences in dissolved solute concentration inside a cell versus outside of the cell
54
What is a hypertonic solution?
solute concentration is less than that inside the cell; cell gains water
55
What is an isotonic solution?
Solute concentration is the same inside of the cell, no net water movement across the membrane
56
What is a hypotonic solution?
A solute concentration that is greater inside the cell than outside the cell; the cell gains water.
57
What is the role of cell walls in reference to tonocity?
Cell walls help maintain water balance
58
Animal cells lack cell walls so what type of solution is ideal? and what happens to the cell if it's in the other environments?
In a hypotonic environment the animal cells take up water until they burst
The ideal environment is an isotonic solution
In a hypertonic solution the animal cells lose water and shrivel however they can still survive
59
How do plant cells behave in different environments?
In hypotonic solutions plant cells swell until the cell wall opposes uptake; the cell wall is now turgid, therefore this is the ideal environment
In an isotonic solution there is no net movement of water into the cell therefore the cell becomes limp and the plant may wilt
In a hypertonic environment the membrane pulls away from the wall and the cell dies via plasmolysis
60
What organisms use a contractile vacuole? and what is important for these organisms?
Protozoans are an example of organisms that use contractile vacuoles. Fresh water organisms need to expend more energy. It's important these organisms are able to control their solute concentrations and water balance also known as osmoregulation. There is more solute in the cell than outside, and they constantly take in water.
61
What do animal cells do to maintain water balance in hypotonic environments?
They need to pump out ions to avoid excessive water uptake
62
How do transport proteins, pumps, and active transport all connect?
Transport proteins are call pumps and they move solutes against their concentration gradients and this is known as active transport
63
Three main ways pumps carry out active transport: ATP-driven pumps
enzymes hydrolyze ATP to promote a conformational change that binds and transports substances against their concentration gradients
64
Three main ways pumps carry out active transport: Light-driven pumps
Similar to ATP-driven pumps but light provides the energy needed to transport a substance
65
Three main ways pumps carry out active transport: Gradient driven pumps
not directly powered but rely on the movement of one substance down its concentration gradient to force the movement of another substance against its concentration gradient
66
How does voltage relate to membranes?
voltage is created by differences in the distribution of positive and negative ions across a membrane
67
What is the electrochemical gradient? and what do the different forces do?
chemical and electrical forces collectively are called the electrochemical gradient, and they drive the movement of ions across a membrane. A chemical force is the ion's concentration gradient. An electrical force is the effect of the membrane potential on the ion's movement.
68
What establishes the membrane potential of animal cells?
Sodium-potassium pumps
69
How does the cell get a negative charge in sodium potassium pumps?
the sodium potassium pumps expel 3 positive ions and imports only two 2 positive ions into the cell and this gives the cell a negative change
70
What are the main electrogenic pumps of plants, fungi, and bacteria? and what gives these cells a negative charge?
Proton pumps. Expelling proteins give these cells a negative charge.
71
What do electrogenic pumps do?
They help store energy that can be used for cellular work in the same way pumping water into a water tower stores energy for later use. This stored energy is in the form of an electrochemical gradient. they produce a membrane potential which is the voltage difference across a membrane
72
What is cotransport and what's an example?
cotransport is when active transport of a solute indirectly drives transport of other solutes. Plants use the gradient of hydrogen ions generated by proton pumps to drive active transport of nutrients into the cell.
73
How are gradient-driven pumps
related to cotransporters? What must have to happen for cotransporters to transport substances?
Gradient-driven pumps are cotransporters that facilitate the movement of two different substances either in the same direction (symporters) or opposite direction of each other (antiporters). Cotransporters must transport both substances and if one is absent the other will still not be transported.
74
What do uniporters do?
they transport only one type of solute and do not function as pumps and are classified as passive transporters.
75
In animal cells how is glucose imported into the cell?
a glucose-Na+ symporter uses the electrochemical Na+ gradient to drive the import of glucose into the cell
76
Compare the plasma membrane potential of animal cells and plant cells.
In animal cells the plasma membrane potential is established by sodium potassium pumps
In plant cells proton pumps are used to establish plasma membrane potential and for transporter within the cell
77
What does the selectivity filter do?
it's a region of the channel that allows only certain ions to pass through
78
Connect ion channels and gatedness
Some ion channels always allow the flow of ions through the membrane, but many are gated and can only flow when the gate is open
79
The electrochemical gradient governs...
the directionality of movement
80
What are voltage gated ion channels?
These channels only open when the membrane potential is within a certain range and are important in propagating signals down the axons of neurons
81
What are ligand-gated ion channels?
They are only open when a certain molecule is bound to the channel (the ligand), the ligand can be a signaling molecule like a hormone or neurotransmitter, ligands also come from within the cell as intracellular signaling molecules
82
What are mechanically gated ion channels?
they respond to changes in mechanical stress on cells or changes in fluidity of the membrane. important for sensation of sound and touch.
83
What do the K+ concentration gradient and K+ leak channels do? How do sodium-potassium pumps play into this?
they play a major role in creating the resting membrane potential across the plasma membrane in animal cells. Sodium potassium pumps create the membrane potential, but potassium leak channels prevent the overshoot of this pumping action-which sets a particular voltage across the membrane.
84
Explain resting potential
The resting potential is different for different types of cells in the body. When channels are open, the membrane potential can change rapidly. When sodium channels are open cells depolarize and the membrane potential moves away from the resting potential and towards 0 mV.
85
Explain how signaling, neurons, and ligands connect
Neurons take in signals along dendrites and the cell body. These signals are ligands which are signaling molecules that bind to receptors on the membrane and cause ion channels to open or are ligand gated ion channels.
86
What does signals in relation to hyperpolarize mean?
Signals may hyperpolarize the cell which makes it less likely to fire off an action potential
87
What does signals in relation to depolarize mean?
Signals may depolarize the cell bringing the membrane potential close to the action potential threshold.
88
What happens if the cell depolarizes enough? Around -40mV
a region at the beginning of the axon called the axon hillock rapidly depolarizes sending off an action potential
89
What do neurons do in relation to action potentials?
they propagate action potentials down their axons as a wave of membrane depolarization
90
What are the three states of voltage-gated sodium channels along the axon?
closed, open, and inactivated
91
Once the threshold potential is reached what happens? What does the influx of Na+ do?
Once the threshold is reached voltage gated sodium channels open. Influx of Na+ rapidly depolarizes the region of the cell membrane which results in a downstream voltage-gated sodium channel opening in a cascading manner
92
What happens during a refractory period?
After being open for a moment the channels enter a refractory period where the channels are desensitized to voltage changes. An inactivation subunit swings into place which blocks the flow of ions. The subunit will not relax until the membrane potential is below the threshold potential. After this period the channel is sensitive to voltage and ready to propagate the next action potential.
93
What do voltage-gated Ca2+ channels do?
In neuron terminals they convert an electrical signal into a chemical signal
94
Vesicles that have neurotransmitters are...
stimulated by the Ca2+ flux and merge with the plasma membrane and release neurotransmitters into the synaptic cleft.
95
What do ligand-gated ion channels in the postsynaptic membrane do?
convert the chemical signal back into an electrical signal
96
What is the role of the synaptic cleft?
The synaptic cleft is a tight domain which reduces the time needed for neurotransmitters to diffuse to their targets on the post-synaptic membrane
97
Connect glycolysis and amount of ATP made? In aerobic eukaryotes about how much of the cell's ATP comes from glycolysis?
Glycolysis is where a small amount of ATP is made from partial oxidation of glucose. In Aerobic eukaryotes about 6% of the cell's ATP comes from glycolysis and the rest comes from later oxidation steps.
98
What is combustion?
uncontrolled oxidation
99
In cells how are glucose and other organic molecules broken down? And based on how this is broken down where does some of the energy go?
They are broken down in a series of steps where electrons are ferried by activated electron carrier molecules. Some free energy is stored in these activated carriers.
100
What are the electron carriers? Give a brief overview
Electrons from organic compounds are first transferred to NAD+. NADH which is the reduced form of NAD+ represents potential energy that can be used later for synthesizing ATP. FAD and FADH2 are similar.
101
What are catabolic pathways?
metabolic pathways that break down larger molecules to release energy and produce smaller metabolites.
102
What is typically the first step in catabolism? What is the universal fuel source and how is it usually catabolized first?
The first step in catabolism is glycolysis. The universal fuel source is glucose, and it is usually catabolized starting with glycolysis.
103
What is aerobic respiration?
consumes organic molecules and O2 creating large quantities of ATP and requires and electron transport chain. most eukaryotes are capable of doing this.
104
What is Anaerobic respiration?
Similar to aerobic respiration but consumes other compounds other than O2 and creates large amounts of ATP but less than aerobic respiration. Also requires ETC. Prokaryotes can do this especially those in hydrothermal vents.
105
What is fermentation?
fermentation is the partial degradation of sugars that occurs without O2 and this yields small amounts of ATP. Many organisms can do this.
106
what do aerobic respiration, anaerobic respiration, and fermentation all begin with?
glycolysis
107
Explain glycolysis
Glycolysis is the breaks down glucose into two molecules of pyruvate. This occurs in the cytosol and used by nearly all organisms. It does not require oxygen and is a very ancient process. It's thought that little O2 was available until around 2.7 BYA so early prokaryotes were thought to use it to generate ATP.
108
What are the two main phases of glycolysis and what occurs in these phases?
The energy investment phase consumes 2 molecules of ATP
The energy payoff phase generates 4 molecules of ATP
109
What does glycolysis yield?
2 molecules of pyruvate and a net production of 2 ATP molecules and 2 activated electron carriers NADH
110
Why might an organism be incapable of respiration? How can glycolysis still provide ATP for the cell?
An organism may not be capable of respiration because O2 isn't available, the cell lacks part of the ETC, the species never evolved respiration. Glycolysis can still provide ATP for the cell by coupling with fermentation, but glucose will not be fully oxidized. This provides significantly lower ATP yields than cellular respiration.
111
What does fermentation consist of?
Fermentation consists of glycolysis plus reactions that regenerate NAD+ which is needed to keep glycolysis going.
112
Explain lactic acid fermentation
pyruvate is reduced by NADH and forms lactate as an end product with no release of CO2. Muscle cells use lactic acid fermentation to generate ATP when O2 is scarce.
113
Explain alcohol fermentation
Pyruvate is converted to ethanol in two steps the first being releasing CO2. This is usually accomplished by yeast, but bacteria may also be used.
114
What are obligate anaerobes
they carry out fermentation or anerobic respiration and cannot survive in the presence of oxygen.
115
What are facultative anaerobes?
they can survive using either fermentation or aerobic respiration. After glycolysis and pyruvate is formed if O2 is present then aerobic cellular respiration can occur and they can go into the mitochondria and into the TCA. If no O2 is present then fermentation occurs and produces ethanol, lactate, or other products.
116
What is the transition step?
Pyruvate must be transported into the mitochondria, and it is converted into acetyl-CoA. If this is occurring in prokaryotes then this happens in the cytosol. This reaction yields NADH and CO2
117
Give brief overview of TCA
It completes the oxidation of pyruvate to CO2. The cycle oxidizes acetyl-CoA. Two molecules of acetyl-CoA are fed into the cycle for every molecule of glucose. The net result is one turn of the cycle produces 3 NADH, 1 GTP, and 1 FADH2 and releases 2 molecules of CO2
118
How does the TCA start?
The acetyl group of acetyl-CoA joins the cycle by combining with oxaloacetate and forms citrate. The next 7 steps decompose citrate back into oxaloacetate.
119
From 2 molecules of pyruvate the TCA yields?
2 ATP, 6 NADH, and 2 FADH2 molecules
120
Explain the overall idea of oxidative phosphorylation
the electrons carried by NADH and FADH2 make up most of the energy extracted from food. The two electron carriers donate electrons to the ETC which is a series of enzymes, proteins, and other molecules which pumps protons into the intermembrane space and produce a proton motive force. Through chemiosmosis the enzyme ATP synthase couples the conversion of ADP--> ATP to the flow of protons back into the matrix
121
Where is the electron transport chain located
in the inner membrane of the mitochondrion
122
What does ATP synthase do?
ATP synthase is not part of the ETC but takes advantage of the work done by the ETC by allowing protons to flow down their concentration gradient and this generates ATP in the process.
123
What is the proton-motive force?
Electron transfer in the ETC powers the pumping of protons from the matrix to the intermembrane space and this produces an electrochemical gradient.
124
How much energy is transferred to ATP during cellular respiration? Where does the rest of the heat go?
1/3 of the energy in a glucose molecule is transferred to ATP during cellular respiration and the rest of the energy is lost as heat
125
What does ATP yield depend on?
Intermediate metabolites may be shuttled off to anabolic processes
Passive transport of protons back into the mitochondrial matrix without passing through ATP synthase
126
What is photophosphorylation?
Process by which chloroplasts and cyanobacteria produce ATP which is a process powered by the absorption of light. ATP molecules are not used to directly fuel the cell but rather hydrolysis of these molecules powers the production of sugars that are stored by the organism until they are broken down by catabolic pathways.
127
What are autotrophs?
producers of the biosphere, producing organic molecules from CO2 and other inorganic molecules
128
What are photoautotrophs?
sustain themselves without consuming other organisms and derive their carbon from CO2 and energy from light. almost all plants are autotrophs
129
What did chloroplasts evolve from?
They are structurally similar to cyanobacteria and these structures are what allow for chemical reactions of photosynthesis.
130
Where is photosynthesis located? How do leaves get their green color? Where are chloroplasts found?
Photosynthesis occurs in the leaves, their green color comes from chlorophyll, chloroplasts are found in the cells of the mesophyll and each mesophyll has 30-40 chloroplasts.
131
What is the function of the stomata?
CO2 enters and O2 exits the leaf via pores known as stomata
132
Where is chlorophyll located?
In the membranes of thylakoids and these are stacked into columns called granum
133
What are the two pathways of photosynthesis?
Light reactions - harnesses light energy
Calvin Cycle - makes sugars
134
Give an overview of light reactions
Light reactions take place in the thylakoids. These reactions split H2O, release O2, Reduce NADP+ to NADPH, Generate ATP from ADP by photophosphorylation. The two types of systems responsible for light reactions are photosystem I and photosystem II.
135
What is the role of thylakoids?
They transform light energy into chemical energy of ATP and NADPH
136
What wavelengths carry more energy?
shorter wavelength photons carry more energy
137
What does a photosystem consist of?
it is a reaction-center complex that is surrounded by light harvesting complexes
138
What are light-harvesting complexes?
they are proteins that are bound to the chlorophyll and other pigment molecules. they transfer resonance energy to the reaction center
139
What does the Reaction-center complex contain
it contains a chlorophyll a dimer and the primary electron acceptor protein. the chlorophyll a dimer is the primary electron donor to return to its ground state it transfers energy to the primary electron acceptor via an electron rather than resonance energy transfer.
140
Which photosystem comes first in light reactions
photosystem II comes first and is best at absorbing 680 nm
photosystem I is best at absorbing 700 nm photons
141
What happens in linear electron flow
Both photosystems are involved and produces ATP and the activated electron carrier NADPH. These will be used by the Calvin Cycle to produce sugars
142
What happens in cyclic electron flow
only photosystem I is used and only produces ATP no NADPH is made. no oxygen is released. generates surplus ATP and satisfies the Calvin cycle when ATP demand is high. Primitive bacteria such as cyanobacteria have PS I but not PS II. cyclic is thought to evolved before linear.
143
On what side are ATP and NADPH produced in relation to photosynthesis?
the stroma-facing side of the thylakoid membrane
144
Where will the Calvin cycle take place and sugar is produced?
the stroma is where the Calvin cycle is produced and sugars will be produced
145
Give an overview of the Calvin Cycle
The cycle regenerates its starting material after molecules enter then leave the cycle. the cycle builds sugars from smaller molecules by hydrolyzing ATP and using the reducing power of electrons carried by NADPH. Carbon enters the cycle as CO2 and leaves as sugar known as (G3P) which will later be converted into glucose.
146
What are the three phases of the Calvin Cycle?
Carbon fixation where CO2 is fixed in a reaction and catalyzed by RuBisCO and combines RuBP with CO2. Reduction of the fixed carbon into G3P. Regeneration of ribulose which will become RuBP and accept CO2 when the cycle repeats.
147
For the net synthesis of 1 G3P...
the cycle must turn 3 times fixing 3 molecules of CO2
148
Talk about C3 plants and problems that occur with them
C3 plants make up about 95% of Earth's plant biomass but they have a problem since RuBisCo has an affinity for CO2 and O2. C3 plants initially fix CO2 via RuBisCo and make the 3-carbon compound 3-phosphoglycerate. C3 plants undergo photoresperation where RuBisCo adds O2 instead of CO2 and produces a 2-carbon compound incompatible with the next step of the cycle. Photorespiration consumes RuBP without producing sugars and this dramatically decreases the efficiency of photosynthesis as much as 50%
149
talk about photorespiration
likely an evolutionary relic since rubisco evolved when the atmosphere had much less O2 and more CO2 and therefore photorespiration was unlikely to occur. It persists since photorespiration limits damaging products of light reactions that build up in the absence of the Calvin Cycle
150
Talk about C4 plants
they minimize photorespiration by incorporating CO2 into the 4-carbon compounds in mesophyll cells This requires (PEP) carboxylase:
PEP carboxylase has higher affinity for CO2
than RuBisCo; it can fix CO2 even when CO2
concentrations are low and O2 is high. These 4-carbon compounds are exported to bundle-sheath cells where they release CO2 to be used in the Calvin cycle
