mod 1.2 - cell function Flashcards
1
Q
What does the permeability of a cell membrane refer to?
A
Its ability to allow the cell to exchange liquids and materials between the cell’s internal environment and the external environment.
2
Q
Why is the movement of materials in and out of a cell is critical to its function and survival?
A
It allows essential materials to enter while keeping waste materials out. It also allows cells to communicate with other cells.
3
Q
What is it called when the cell membrane is selective about the materials that it allows in and out of the cell?
A
This characteristic is known as being semipermeable.
4
Q
What are cell membranes permeable to?
A
Small molecules and lipid-soluble molecules that can move freely through the phospholipid bilayer.
5
Q
Small, uncharged molecules:
A
Oxygen and carbon dioxide.
6
Q
Lipid-soluble, non-polar molecule:
A
Alcohol, chloroform, steroids.
7
Q
Small, polar molecule:
A
Water, urea.
8
Q
Small ion:
A
Potassium ion, sodium ion, chloride ion. –> impermeable; ion travels through protein channels.
9
Q
Large, polar, water-soluble molecule:
A
Amino acid, glucose. –> impermeable; molecule travels through protein channels.
10
Q
What are cell membranes impermeable to?
A
Most water-soluble molecules, ions (atoms or molecules with charged regions but no overall charge), polar molecules (molecules with charged regions but no overall charge).
11
Q
Where do impermeable substances pass through?
A
Specific protein channels in the cell membrane.
12
Q
What is diffusion?
A
Diffusion is the net movement of molecules, passively (does not require energy because it occurs from the concentration gradient), along a concentration gradient (from a region of high concentration to a region of low concentration).
13
Q
Solute:
A
Material dissolved in the solvent to form a solution.
14
Q
Solvent:
A
Substance that dissolves the solute to form a solution (eg: water is a common solvent)
15
Q
Solution:
A
Solution: a mixture in which a solute is dissolved in a solvent.
16
Q
What are the two types of diffusion across membranes?
A
Simple diffusion and facilitated diffusion.
17
Q
What is simple diffusion?
A
A form of diffusion that does not require the assistance of membrane proteins; small non-charged molecules or lipid soluble molecules pass between the phospholipids to enter or leave the cell, moving from areas of high concentration to areas of low concentration.
18
Q
What is facilitated diffusion:
A
A form of diffusion that DOES require the assistance of membrane proteins; because the substances are impermeable.
19
Q
What is the term when transport proteins become fully occupied as the concentration of the transported substances increases?
A
Saturation.
20
Q
In facilitated diffusion, are the membrane transport proteins specific for particular particles?
A
Yes, transport is selective; some particles are transported and others are not.
21
Q
What are the two main types of membrane transport involved in facilitated diffusion?
A
Channel proteins and carrier proteins.
22
Q
What are channel proteins?
A
Channel proteins don’t usually bind with molecules being transported; they function like pores that open and close to allow the passage of specific molecules.
Channel proteins are mainly involved in the passage of water-soluble polar particles, such as ions. (eg: Na+, K+ and Cl-)
23
Q
What are carrier proteins?
A
Carrier proteins bind the molecules being transported.
This causes the protein to undergo a change in shape (or conformation) that allow specific molecules to be transported across the membrane.
After the molecule has crossed the membrane, the original shape of the protein is restored.
24
Q
What is osmosis?
A
Osmosis refers to the net diffusion of water molecules across a semipermeable membrane. (passive)
25
What is the osmotic gradient?
The net diffusion of water occurs through a semipermeable membrane from a diluted to a concentrated solution along its own concentration gradient.
26
What is osmotic pressure?
The pressure causing the water to move along this osmotic gradient.
27
What is high turgor?
Plant cells with high internal fluid pressures.
28
What are the terms used to describe the differences between solutions? (osmosis)
Isotonic, hypotonic and hypertonic
29
What are isotonic solutions?
The solutions being compared have equal concentration of solutes.
30
What are hypertonic solutions?
The solution with a higher concentration of solute (hence lower concentration of free water molecules).
31
What are hypotonic solutions?
The solution with a lower concentration of solute (hence higher concentration of free water molecules).
32
What are halophiles? (give eg)
Bacteria that are adapted to extremely salty environments, such as the pink salt lakes in NSW.
They survive by retaining much higher ion concentrations within their cells; and they also produce small, osmotically active molecules to reduce the osmotic gradient, which prevents the loss of water to their salty environments.
Their proteins are also specialised to function normally, despite the high concentration of salts in the cytosol.
33
Describe osmosis in RBC.
If red blood cells are placed in freshwater, the cells absorb so much water by osmosis that they swell and may eventually burst, releasing red pigment into the water. Conversely, if red blood cells are placed in a solution that is more concentrated than their cytosol, water leaves the red blood cells by osmosis, causing them to shrink.
34
What is passive transport? (give eg)
Diffusion, facilitated diffusion and osmosis are examples of passive transport, as they don't require energy to move particles across the cell membrane..
35
What is active transport?
Active transport involves the cell using energy to transport particles across the membrane.
36
What is selectivity in cell membranes?
Means that some substances are transported but others aren’t.
37
What is saturation in cell membranes?
Means that there is no increase in the rate of transfer when all transport molecules are open.
38
What is competitive inhibition in cell membranes?
Means that one substance can inhibit the transport of another substance by using the same transport protein.
39
Compare facilitated diffusion and active transport.
Unlike facilitated diffusion (which occurs through either channel or carrier proteins), active transport only occurs through carrier proteins.
Active transport requires energy (ATP), meaning that it can move against the concentration gradient (from low to high concentrations), unlike facilitated diffusion which can only move down the concentration gradient.
40
What is endocytosis?
Active transport; where cells take in materials in bulk by forming new vesicles from the cell membrane.
During endocytosis, a small area of the cell membrane sinks inwards to form a pocket; and as this pocket deepens, materials near the cell membrane are enclosed by the membrane, which then pinches off to form a vesicle.
The vesicle then transports the substance to where it is required within the cell.
41
What are the three types of endocytosis?
Phagocytosis, pinocytosis and receptor-mediated endocytosis.
42
What is phagocytosis?
When a cell engulfs a solid material by wrapping temporary cytoplasmic extensions called pseudopodia around it. This forms a membrane-bound structure called a phagosome. The material will then be digested when the food vacuole fuses with a lysosome that contains enzymes.
43
What is a phagosome?
When temporary cytoplasmic extensions called pseudopodia wraps around solid material forming a membrane-bound structure called a phagosome.
44
What is pinocytosis?
When the cell membrane engulfs liquid that contains dissolved molecules.
45
What is receptor-mediated endocytosis?
A type of pinocytosis that engulfs specific substances. Protein receptors located on the surface of the cell membrane respond to particular molecules, binding to the molecule and triggering the engulfment of the substance into the cell.
46
What is exocytosis?
Active transport; a process by which the contents of a cell vacuole are released to the exterior through fusion of the vacuole membrane with the cell membrane.
47
What is the process of exocytosis?
When a secretory vesicle membrane and the cell membrane come into contact, specific proteins alter the arrangement of the phospholipids in the phospholipid bilayer.
The fluid and dynamic nature of the cell membrane then enables the two membranes to fuse.
Once the membranes have fused, the contents of the secretory vesicle are released out of the cell → this process is exocytosis (ayo epic?)
The vesicle membrane becomes a permanent part of the cell membrane; the cell membrane is continually recycled as vesicles fuse during exocytosis, and are conversely formed and released during endocytosis.
48
What is exocytosis used for?
In addition to being used for secreting proteins, exocytosis is also involved in the release of cellular waste and the breakdown products from lysosomes.
49
What are factors affecting the rate of diffusion?
Concentration: the greater the difference in concentration gradient, the faster the rate of diffusion. When the concentration is equal on both sides of the membrane, the net diffusion is zero, even at high temperatures.
Temperature: the higher the temperature, the higher the rate of diffusion, as increasing temperature increases the speed at which molecules move.
Particle size: the smaller the particles, the faster the rate of diffusion.
50
Why do larger cells have smaller SA?
Larger cells have greater metabolic needs, so they need to exchange more nutrients and waste with their environment; however, as the size of a cell increases, the SA:V of the cell decreases.
Because of this SA:V relationship, larger cells don’t have a proportionally larger surface area of cell membrane for the efficient exchange of nutrients and waste.
Smaller cells can exchange matter with their environment more efficiently.
THIS IS WHY CELLS DIVIDE.
51
What are the three ways of increasing SA:V?
Three ways of increasing the membrane surface area of cells without changing cell volume are: cell compartmentalisation, a flattened shape and cell membrane extensions.
52
How does cell compartmentalisation increase SA:V?
Allows organelles to have the right conditions and concentration of enzymes and reactants for a particular function, making processes in the whole cell highly efficient.
Cell compartmentalisation also allows eukaryotic cells to be much bigger than prokaryotic cells, because it:
Reduces the amount of exchange that needs to occur across the cell membrane to maintain an environment suitable for all cell functions.
Creates more space for membrane-bound enzymes, allowing increased activity in the cell.
53
How does a flattened shape increase SA:V?
As a cell increases in volumes, the distance from the centre of the cell to the cell membrane also increases.
The rate of chemical exchange (diffusion) from the centre of the cell to the surrounding environment may then become too low to maintain the cell.
One way to counteract this effect is to be flatter. eg: red blood cells and lung epithelium
54
How does cell membrane extensions increase SA:V?
Cells involved in absorbing nutrients or secreting wastes counteract the SA:V problem by extending the surface area of their cell membranes. eg: microvilli in some animal cells and root hairs in plants.
55
Why would a flattened shape not be useful for cells involved in absorbing nutrients or secreting wastes?
Because they require an increased surface area in particular regions of the cell.
56
What are the two groups organisms can be divided into depending on the strategies they use to obtain organic compounds (source of energy)?
Autotrophs and heterotrophs.
57
What are autotrophs?
They make their own organic compounds from inorganic compounds found in the soil and the atmosphere.
The conversion of inorganic compounds into organic compounds is called carbon fixation; as the autotroph ‘fixes’ inorganic carbon into organic molecules, such as glucose.
Also called producers, autotrophs include all of the green plants that carry out photosynthesis.
58
What are heterotrophs?
They obtain organic compounds by consuming other organisms.
| Also called consumers, heterotrophs consist of all animals and fungi.
59
What are organic compounds?
Characteristic complex compounds that contain carbon and hydrogen that organisms produce.
60
What are inorganic compounds?
Compounds without carbon-hydrogen bonds.
61
Eg of inorganic compounds.
Water, oxygen, carbon dioxide, nitrogen, minerals.
62
Eg of organic compounds.
Carbohydrates, lipids, proteins, nucleic acids.
63
What are carbohydrates?
(eg: glucose, sucrose, starch and cellulose) important energy sources and structural components of organisms.
The basic subunits of carbohydrates are simple sugars, monosaccharides (single sugars), disaccharides (two sugars joined together), and polysaccharides (many sugars joined together in long chains).
Carbohydrates have hydrogen atoms in a 2:1 ratio with oxygen atoms.
64
What are lipids?
Play an important role in cell membranes, lipids consist of fats and oils, which are important for energy storage. Lipids are composed of a glycerol ‘head’ and fatty acid ‘tails’.
65
What are proteins?
Composed of amino acids and have many functions; some are enzymes, hormones, antibodies or carrier proteins. Proteins form part of the cell membrane. Organisms have their own unique proteins.
Their diversity comes from the 20 possible amino acid subunits, linked by peptide bonds into polypeptide chains, two or more of which are folded into a complex 3D-shaped structure (tertiary structure).
Proteins are constructed in each cell under coded directions from DNA.
66
What are nucleic acids?
Carry genetic information of cells, in the forms of DNA or RNA.
DNA (adenine, thymine, cytosine, guanine): carries the information needed to assemble proteins from amino acid subunits, and this genetic information is passed from cell to cell in cell division.
RNA: plays a major role in the manufacture of proteins within cells.
67
What are structural organic molecules?
These molecules and vitamins are small, organic molecules that are vital for normal cell function.
Some of these can be synthesised, but others must be obtained through diet.
Water-soluble vitamins must be consumed regularly because they cannot be stored in body tissues. Lipid-soluble vitamins can be stored. (Vitamins are needed to work with enzymes).
68
What is metabolism?
Refers to the total of all the chemical reactions in a living organism.
69
What is excretion?
The removal of substances that once formed part of the body of the organism. It occurs largely in the kidneys. THIS IS NOT POO- see egestion
70
What is egestion?
In mammals, the removal of undigested food (poo) from the gut via the anus.
71
Why must waste removal occur?
Accumulation of these waste substances, such as CO2 from cellular respiration and nitrogenous wastes from the breakdown of proteins and nucleic acids (DNA & RNA) have to be removed to ensure balance is maintained in the cell and organism, through excretion.
72
How do cell membranes regulate the transport of waste materials?
Through passive transport. (eg: osmosis of water, simple diffusion of oxygen, carbon dioxide, ammonia and alcohol; facilitated diffusion of urea, glucose and ions)
Active transport. (eg: urea, toxins and ions being removed against their concentration gradient via exocytosis and endocytosis).
73
Compare waste removal in heterotrophs and autotrophs.
Excretion in autotrophs are considered by-products rather than waste as elimination is subtle.
Plants don’t have excretory organs; although leaves could be regarded as excreting any excess carbon dioxide or oxygen.
Compared to heterotrophs, autotrophs produce almost no true waste, as they have a lower metabolic rate and can reuse gases and contain fewer protein molecules → therefore producing less nitrogenous waste.
74
Waste removal in unicellular heterotrophs:
In unicellular heterotrophs, waste products can be released directly into the environment. (eg: Paramecium and Amoeba live in freshwater and expel wastes through their membrane into the environment; through contractile vacuoles which allow water to pumps wastes out)
75
Waste removal in multicellular heterotrophs:
In complex heterotrophs, specific excretory organs are needed.
76
How is carbon dioxide formed as a waste and how is it excreted?
Produced as a waste during cellular respiration when carbohydrates or lipids are broken down.
These are removed by:
Diffusing across moist respiratory membranes (eg: lungs for mammals) and breathed out.
Diffusion or gills are responsible for this in aquatic animals. (eg: animal groups that use gills include fish, crustaceans, some amphibians and the larval stage of some insects)
If carbon dioxide builds up, it lowers pH → increasing acidity of the blood and extracellular fluid.
77
How is water formed as a waste and how is it excreted?
If extra water is produced in cellular respiration, it would first be incorporated into normal body fluids.
Any excess from this is expelled through breathing out water vapour (eg: American bison) or with urine from the kidneys.
Urine can be more or less diluted as part of the body’s homeostatic regulatory process.
Freshwater animals don’t have to remove excess water, which is drawn in by osmosis. (eg: Paramecium)
78
How are nitrogenous wastes formed as a waste and how is it excreted?
These are produced when proteins break down (also producing lipids or carbohydrates used for energy) or when cells break down and recycle nucleic acids (DNA & RNA)
They are removed because they can be toxic, and this is done via excretory organs.
79
How are nitrogenous wastes removed in mammals?
Nitrogenous waste is managed by the liver, regulated by the kidneys and excreted as urea in the urine.
In the kidneys, specialised structures called nephrons filter the blood to regulate the concentration of water and soluble substances. → It makes sure that urea is filtered from blood into urine, and this maintains the salt-water balance of the body.
80
What is photosynthesis?
The biochemical process of photosynthesis involves plants and photoautotrophic organisms obtaining energy from sunlight to make their own organic compounds.
81
Where are chloroplasts found in vascular plants?
Chlorophyll molecules absorb energy from sunlight.
In vascular plants, chloroplasts are found in the mesophyll of cells.
These mesophyll cells are packed with chloroplasts and are the main sites of photosynthesis. They are located near the upper surface of the leaf, meaning that the chloroplasts have maximum exposure to sunlight, increasing the rate of photosynthesis.
82
Where does photosynthesis take place?
Photosynthesis takes place inside the chloroplasts, where the grana stacks contain the chlorophyll pigments where reactions using light energy occur during photosynthesis.
83
Where are chloroplasts made?
The thylakoids are where chlorophyll is made.
84
Where is the stroma?
The outer membrane is highly permeable and the inner membrane is impermeable and surrounds the area filled with a liquid called stroma.
Stroma contains a number of enzymes, spherical DNA and ribosomes.
85
How does photosynthesis occur in non-green plants, protists and cyanobacteria?
Some plants have colourful leaves, they still contain chlorophyll but also contain other pigments, including phycobiliproteins and carotenoids, which mask the green chlorophyll.
Phycobiliproteins and carotenoids assist in photosynthesis by absorbing different wavelengths of light. Phycobiliproteins are useful in deep water, where only green wavelengths can penetrate.
Other pigments protect plants from overexposure to sunlight and attract pollinators.
86
Why is photosynthesis important?
Photosynthesis is very important because carbon fixation and the production of plant matter is essential in providing energy and biomass in both aquatic and terrestrial ecosystems.
Plants produce all the organic compounds from glucose they produce by photosynthesis, as long as they have the necessary minerals.
87
What is the general word + chemical equation of photosynthesis?
see sticky-notes.
88
What is the word + chemical equation of light-dependent reactions?
see sticky-notes.
89
What is the word + chemical equation of dark reactions?
see sticky-notes.
90
What are the two stages of photosynthesis?
Light-dependent reactions and light-independent (dark) reactions.
91
What are light-dependent reactions?
This is where chlorophyll captures solar energy and uses it to produce adenosine triphosphate (ATP).
During this process, photolysis occurs (the splitting of water molecules), where water is split into hydrogen ions and oxygen gas.
Light-dependent reactions occur on the thylakoid membranes (grana) of the chloroplast.
92
What is photolysis?
The splitting of water molecules in photosynthesis into hydrogen ions and oxygen gas.
93
What are light-independent reactions?
Also called dark reactions (they don’t require solar energy), produce glucose, water and adenosine diphosphate (ADP).
ATP made in stage one provides the energy needed for dark reactions.
This energy combines carbon dioxide with hydrogen ions to form glucose and water.
These take place in the stroma (fluid part) of the chloroplast.
94
What affects the rate of photosynthesis?
Light intensity, carbon dioxide concentration and temperature. --> The factor that is present in the smallest amount is the limiting factor.
95
What is cellular respiration?
Where cells release chemical energy by breaking down glucose molecules, producing ATP, as well as carbon dioxide and water.
96
Light compensation point (in plants):
The light compensation point is the level of light that both of these biochemical reactions are equal and there is no net exchange of oxygen, as the amount of oxygen used is equal across these two.
97
Cellular respiration in eukaryotic cells:
Cellular respiration uses glucose and oxygen to produce usable energy, along with carbon dioxide which is a waste product.
Cells obtain energy from organic compounds (eg: glucose) and transform this chemical energy in organic compounds into a more usable form of chemical energy; stored in the bonds of ATP.
98
Why is cellular respiration important for the ecosystem?
This process is not only important for cells, but the ecosystem, as biochemical processes in plants and animals are part of the carbon and oxygen cycles that sustain life.
99
Why is cellular respiration important for the organism?
All cells require energy to carry out their functions, energy being the ability to cause change.
Chemical energy is stored in the bonds that join atoms together, and when, for example, the carbon-hydrogen bonds in glucose are broken down, energy is released and stored in ATP molecules where it is readily available.
100
What is ATP? (adenosine triphosphate)
The ATP molecule contains two high-energy bonds between the inorganic phosphate groups, and are readily available to be broken down.
Each energy packet can be used to produce an ATP molecule from ADP and a phosphate ion.
101
What are the two main stages of cellular respiration?
Glycolysis and aerobic or anaerobic respiration.
102
What is glycolysis?
First process that takes place in the cytosol of the cell and is anaerobic; and involves the splitting (lysis) of glucose into two pyruvate molecules.
Glycolysis uses two ATP molecules in breaking down one glucose molecule, but it produces four more (net gain of two ATP molecules).
This process is common across both aerobic and anaerobic respiration; however after this stage is dependent on oxygen supply.
103
What is aerobic respiration?
Occurs in mitochondria and converts ADP into ATP. During this, the two pyruvate molecules are then broken down to produce carbon dioxide, water and 36 ATP molecules.
104
What is anaerobic respiration?
Also known as fermentation, it occurs in the cytosol, and there is no further formation of ATP. The purpose of this is to prevent accumulation (build-up) of the pyruvate, as this would slow the chemical reaction. With this, glycolysis continues and the pyruvate is converted into either lactic acids (in most animals) or carbon dioxide and alcohol (in most plants and microorganisms).
105
How is oxygen transported in mammals?
In mammals, oxygen is made available to cells via the lungs.
In the lungs, oxygen diffuses from the alveoli into the blood, and the oxygen combines with a protein - hemoglobin to form oxyhaemoglobin.
This is then transported to cells by the circulatory system, and is released from the oxyhaemoglobin, diffusing into cells which then use it for aerobic respiration.
106
What is the general word + chemical equations of cellular respiration?
see sticky-notes
107
What is the general word + chemical equations of aerobic respiration?
see sticky-notes
108
What is the general word + chemical equations of anaerobic respiration?
see sticky-notes
109
What are the organelles specialised for processing and removing waste products from cells in eukaryotes?
Lysosomes and proteasomes.
110
What are proteasomes?
Found in the cytoplasm and nucleus of all eukaryotes, archaea and some bacteria, these are protein complexes that degrade damaged proteins by breaking their peptide bonds.
This chemical reaction of the degradation of proteins is called proteolysis and is catalysed by the enzyme proteases.
They regulate the concentrations of proteins inside the cell and destroy proteins that are misfolded.
111
What are lysosomes?
Float in cytosol, fusing with vesicles that contain waste products or damaged cellular structures.
The digestive enzymes inside lysosomes break down waste products into smaller molecules.
Once these smaller molecules are small enough, they are either reused, or transported out of the cell membrane (exocytosis).
112
What organ prepares wastes?
The liver.
It detoxifies harmful chemicals. (eg: alcohol and some drugs)
It breaks down amino acids to release ammonia, which it then converts largely into urea or uric acid.
The waste products from the liver then travel in the bloodstream to the kidneys for excretion in the urine.
113
What excretes wastes?
The kidneys.
Filtration of blood: blood passing through each kidney is filtered through blood vessel walls to form a primary filtrate in the nephron tubules.
Reabsorption of useful substances back into the blood: most of the useful substances from the primary filtrate are reabsorbed as it passes along each nephron tubule.
Active secretion of extra wastes into the filtrate (forming waste called urine): extra unwanted substances may be secreted into the fluid in the tubule before it passes as urine from the kidney to the bladder.
Elimination of the unwanted urine from the organism: the formation of urine involves passive filtration, selective reabsorption and secretion and the passive removal of water.
114
What are enzymes?
Enzymes are protein molecules that catalyse biochemical reactions and regulate biochemical pathways.
Most enzymes are globular-type protein molecules, meaning they are formed from long chains of amino acids that coil and fold into a compact structure.
115
What is enzyme specificity?
Enzymes catalyse biochemical reactions by binding to a specific substrate (most enzymes have evolved to be highly specific, binding to only one substrate, but other enzymes can act on multiple substrates that are similar.
116
What is enzyme catalytic power?
Enzymes don’t make reactions occur that would not occur on their own; they only make reactions occur more quickly by reducing the activation energy.
117
Are enzymes able to be reused?
Enzymes aren’t consumed when they catalyse reactions, as they are not products in the reaction. At the end of the reaction, enzyme molecules are reused over and over again.
118
What is a substrate?
A molecule upon which an enzyme acts. The enzyme can break down the substrate into smaller molecules or join the substrate with other molecules to make a large molecule. Substrates include carbohydrates and proteins we eat, which are digested by enzyme action. Glucose is an example of a substrate used by enzymes in cellular respiration.
119
What are catalysts?
Substances that accelerate the rate of any chemical reaction without changing.
120
How is energy released in cellular respiration?
ATP molecule splits off one of its three phosphates becoming ADP + phosphate. The energy holding that phosphate molecule is now released and able to do work for the cell.
121
What is the active site?
The active site of enzymes is a pocket in the enzyme’s structure formed from the tertiary (3D) folding of the protein.
The enzyme’s active site is a complex 3D shape that interacts with a specific substrate to catalyse a specific reaction.
122
What is the enzyme-substrate complex?
When the active site binds to the substrate, it forms an enzyme-substrate complex.
123
What is the Lock-and-Key Model?
Describes the active site and the specific substrate as fitting together like a lock and key.
If the ‘key’ (substrate) doesn't fit in the ‘lock’ (the enzyme’s active site), then no reaction occurs.
This is the older version of the interaction model, and is now thought to be less accurate.
124
What is the Induced-Fit Model?
States that when a substrate binds to the active site of an enzyme, the active site changes shape.
This model is more accurate.
We now know that the active site is flexible, capable of changing its shape to conform to the shape of the substrate and achieve a tighter fit.
125
What are catabolic reactions?
Break down substances, they are exergonic, because they release energy. eg: cellular respiration: break down of fuel molecules, digestion: break down of food.
126
What are anabolic reactions?
Produce larger molecules from smaller substrates. Anabolic reactions are endergonic because they require energy to form bonds between molecules.
eg: photosynthesis: build up of sugars, protein synthesis: build up of polypeptides from peptide bonds.
127
Plant enzymes in photosynthesis:
Enzymes play a role in photosynthesis, particularly during the light-independent reactions. In this, carbon dioxide combines with a ribulose biphosphate, and an enzyme called RuBisCo catalyses the fixation of carbon dioxide → proceeds to produce glyceraldehyde-3-phosphate, which the plant uses to make carbohydrates.
128
How do herbicides work?
```
Some herbicides (chemicals that kill plants) work by blocking plant enzyme activity.
A tiny herbicide molecule attaches to the enzyme active site and stops it from working; these are called irreversible inhibitors.
Some plants adapt to herbicides by changing their amino acids (therefore their enzyme structure) and continue to work.
```
129
Importance of fruit enzymes?
Contain proteases that speed up the breakdown of proteins that can be used as medicine.
130
Fungi enzymes are what?
Many fungi are saprotrophic (they cause decay by releasing enzymes into the dead animal or plant).
These break down complex compounds into simple, soluble compounds that can be absorbed by the decomposer.
Fungi and their enzymes are an essential part of decomposition cycles in the environment → they convert complex organic compounds into easily assimilated nutrients for other species.
131
What do fungi enzyme: cellulases do?
Soften wood in paper production of biofuels.
132
What do fungi enzyme: peroxidases do?
Remove pollutants in waste water treatment.
133
What do fungi enzyme: lipases do?
Degrade organic matter in sewage sludge treatment.
134
What are factors that affect enzyme activity?
Temperature, pH and the concentration of the substrate and enzyme.
135
What happens to enzyme when the temperature becomes higher than the optimum temperature?
However, proteins and enzymes can be denatured at high temperatures, causing hydrogen bonds and hydrophobic interactions that create coiled, globular, tertiary (3D) shape of the enzyme are broken
The substrate can no longer bind to the changed active site of the enzyme, and denaturation is usually irreversible.
Human enzymes have their optimum activity at a temperature of 36-38℃ (matches our body temperature).
Many animal enzymes will begin to denature above 40℃.
Taq polymerase is an enzyme originally found in bacteria living in hot springs, and has an optimum temperature of 70℃.
Enzyme adaptations have evolved over time to enable the species to live successfully in their natural environment.
136
What happens to enzyme when the temperature becomes lower than the optimum temperature?
When below their optimum temperature, enzymes will slow down, making collisions less likely to occur, and the rate of reaction will decrease.
Enzymes aren’t denatured at low temperatures, they just act more slowly. (eg: this is why the decomposition of food and ripening of fruit is slower in a refrigerator)
137
How does pH affect enzymes?
If enzymes are taken too far or below their optimum pH, their tertiary structure is affected, the enzyme may become denatured.
If the pH of the environment is not ideal, the micro-environment of the active site may be altered to provide a different pH and allow the reaction to take place.
138
Examples of optimum pH and enzymes:
Amylase starts the digestion of starch in the mouth and has an optimum pH of about 7.
Pepsin is found in the stomach and has an optimum pH of about 2 from the presence of hydrochloric acid.
Trypsin is found in the small intestine and has an optimum pH of about 8.
Lactase is a digestive enzyme that breaks down lactose into glucose and galactose.
139
How does the concentration or the substrate and enzyme affect enzyme activity?
If the enzyme concentration is high compared to that of the substrate, the reaction will occur over a short period of time, because the more enzyme molecules that are available, the more active sites there will be for the substrate to bind to.
This speeds up the rate of reaction until saturation point is reached.
When all sites are taken, the saturation point is reached.
If the enzyme concentration is lower compared to that of the substrate, the reaction will be slower, because there are few active sites compared to the number of substrate molecules.
140
What is the saturation point?
The stage at which no more of a substance can be absorbed into a vapour or dissolved into a solution.
141
How does cell compartmentalisation help enzymes?
Cell compartmentalisation offers specific environments in which conditions (pH, temperature) are optimal for enzymes to catalyse reactions.
Through organelles, enzyme’s conditions are matched, and there will be high concentrations of the enzymes and substrates for that organelle's function. (eg: in chloroplasts for photosynthesis and in mitochondria for cellular respiration)
142
What are the two types of enzyme inhibition?
Competitive inhibition and non-competitive inhibition/allosteric inhibition.
143
What is competitive inhibition?
Competitive inhibition: involves an inhibitor binding directly to the active site of the enzyme; and the substrate is then unable to bind to the enzyme.
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What is non-competitive inhibition?
Non-competitive inhibition: involves an inhibitor molecule binding to the enzyme in a position other than the active site. This changes the shape of the enzyme’s active site, so that the substrate no longer fits.
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What is feedback inhibition?
Feedback inhibition occurs when a product that is produced late in a biochemical pathway is also an inhibitor of an enzyme earlier in the pathway.
As the amount of the inhibiting product increases, the amount of enzyme molecules being inhibited also increases, this in turn reduces the amount of the inhibiting product.
As the level of inhibiting product is reduced, less of it will bind to the enzymes, allowing them to function again.
Feedback inhibition is an important mechanism in controlling enzyme activity.
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What is phosphorylation?
The binding of a phosphate group to a protein is known as phosphorylation.
The removal of a phosphate group from proteins is known as dephosphorylation.
These both change the structure (or conformation) of proteins, and therefore both can regulate enzymes.
eg: the phosphorylation of glycogen synthase inhibits its ability to interact with glucose. The phosphorylation of glycogen synthase is performed by another enzyme, called glycogen synthase kinase 3.
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What are cofactors?
Cofactors can be inorganic ions such as iron (Fe2+), magnesium (Mg2+) and zinc (Zn2+), or organic molecules such as proteins, vitamins and ATP.
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What are coenzymes?
Small, non-protein organic cofactors are known as coenzymes.
For certain enzymes, a specific coenzyme is required to catalyse reactions; often the coenzyme is structurally altered during the reaction, but afterwards reverts to its original form, which allows it to be reused.
There are many types of coenzymes, such as vitamins, ATP, nicotinamide adenine dinucleotide (NADH), flavin adenine dinucleotide (FADH2) and nicotinamide adenine dinucleotide phosphate (NADPH).
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What do cofactors do?
Some enzymes need additional components to enable them to catalyse a reaction, these are known as cofactors, and they bind to the enzymes.
