Unit 2 (KA1-2)

Question 1

Oxygen

Answer 1

The final hydrogen acceptor at the end of the electron transport chain.

Combines with hydrogen to make water.

This removes hydrogen and keeps the citric acid cycle and electron transport chain running.

Question 2

Ethanol

Answer 2

Produced along with carbon dioxide by the fermentation of pyruvate in the cytoplasm of plant and yeast cells.

Used to remove pyruvate to keep glycolysis running.

Question 3

Lactate

Answer 3

Produced in the cytoplasm as a result of the fermentation of pyruvate in the cytoplasm of animal cells.

Used to remove pyruvate to keep glycolysis running.

Question 4

Fermentation

Answer 4

Anaerobic respiration (without oxygen),

Glucose is partially broken down in the cytoplasm creating 2 ATP only - the net gain from glycolysis.

Question 5

Metabolism

Answer 5

The thousands of integrated biochemical reactions that occur within a living cell.

Question 6

Metabolic pathways

Answer 6

Integrated sequences of chemical reactions within cells.

Each step is controlled by a different enzyme.

They contain reversible and irreversible steps and alternative routes.

Question 7

Anabolic (synthesis) reactions

Answer 7

Build up large molecules from small ones.

Require energy.

eg. protein synthesis.

Question 8

Catabolic (degradation) reactions

Answer 8

Break down large molecules into smaller ones, releasing energy.

eg. respiration, digestion (starch to maltose using amylase)

Question 9

Fluid mosaic model

Answer 9

Describes the structure of cell membranes - a double layer (bilayer) of phospholipids with proteins floating in it.

The cell membrane is the boundary of the cell, and controls entry and exit of materials.

Many of the proteins are enzymes.

Question 10

Organelles

Answer 10

Compartments inside cell, which are made of membrane.

They are the sites of specific chemical reactions. eg. mitochondria (respiration)

Internal cell membranes containing enzymes, provide a large surface area for reactions.

Question 11

Membrane proteins

Answer 11

Globular proteins which act as channels, pores, pumps, enzymes, receptors and antibodies.

Question 12

Diffusion

Answer 12

The movement of particles from a high to a low concentration along a concentration gradient.

Small molecules pass between the phospholipids, larger or charged particles need a channel protein or pore.

Question 13

Active transport

Answer 13

The movement of molecules and ions from a low to a high concentration, against the concentration gradient.

Requires ATP and a specific carrier protein in the membrane.

Question 14

Multi-enzyme complex

Answer 14

A group of enzyme molecules embedded in a membrane, which catalyse the steps of a metabolic pathway in a specific order for maximum efficiency.

Question 15

Activation energy

Answer 15

The energy required to start a reaction, by breaking the bonds in the reactants.

Question 16

Enzymes

Answer 16

Globular protein molecules that act as biological catalysts.

They reduce the activation energy required to start a reaction, so that it can occur rapidly at cell temperature.

They take part in a reaction but are unchanged at the end.

Question 17

Active site

Answer 17

The area on the surface of an enzyme molecule where the substrate binds.

Enzyme and substrate are complementary, so fit together exactly, making enzymes specific for their particular substrate.

Question 18

Induced fit

Answer 18

Proteins are flexible molecules, so when the substrate enters the active site of an enzyme, it changes shape slightly to fit the substrate better.

Question 19

Affinity

Answer 19

Attraction.

Substrate molecules have a high affinity for the active site of an enzyme.

Products have a slightly different shape, don’t fit as well into the active site and are released.

Products have a low affinity for the active site.

Question 20

Orientation of reactants

Answer 20

When 2 or more substrates enter the active site of an enzyme (during an anabolic reaction), they need to be the correct way up for the reaction to proceed.

The shape of the active site will determine how the substrates align themselves.

Question 21

Factors affecting enzyme action

Answer 21

Temperature, pH

Enzyme concentration, substrate concentration

Inhibitors

Question 22

Denatured

Answer 22

Extremes of temperature or pH affect the bonds that maintain the 3D shape of an enzyme.

If the bonds are disrupted, the shape of the enzyme changes, affecting the shape of the active site.

The substrate no longer fits in and the enzyme is said to be denatured.

Question 23

Substrate concentration

Answer 23

The rate of an enzyme controlled reaction will increase with increasing substrate concentration, until all active sites are saturated and the reaction rate levels out.

Enzyme concentration has then become the limiting factor.

Question 24

Control of metabolic pathways

Answer 24

Metabolic pathways can be controlled by :

1) Switching off the gene for an enzyme so that the enzyme is not made (ie. by controlling gene expression)
2) Using inhibitors to reduce the activity of enzymes that are continually expressed.

Question 25

Competitive inhibitors

Answer 25

Compete with the substrate for the active site of the enzyme, as they have a similar shape to the substrate.

They block the active site so that the substrate can’t fit in.

The reaction rate can be increased by increasing substrate concentration.

Question 26

Non-competitive inhibitors

Answer 26

Do not have a similar shape to the substrate.

They attach to an area away from the active site, which alters the shape of the enzyme, and therefore the shape of its active site. The substrate can no longer fit in and the rate of reaction decreases.

If the inhibitor is removed, the effect is reversed.

Increasing the substrate concentration will have no effect.

Question 27

Feedback (end product) inhibition

Answer 27

The end product of a metabolic pathway reaches a critical level, and inhibits an enzyme earlier in the pathway. (It acts as a non-competitive inhibitor).

This blocks the pathway and prevents further synthesis of the product.

If the end product starts to run out, the effect is reversed.

It is an example of negative feedback control.

Question 28

Respiration

Answer 28

A series of vital metabolic pathways which are responsible for the production of ATP in cells.

Question 29

ATP

Answer 29

Adenosine triphosphate (adenosine + 3 phosphate groups)

The 3rd phosphate is attached with a high energy bond that can be broken easily to release large amount of energy when required.

Acts as an energy storage and transfer molecule in cells, linking catabolic and anabolic reactions.

Question 30

ADP

Answer 30

Produced when the 3rd phosphate is removed from ATP, which breaks the high energy bond and releases energy rapidly.

ATP ——————-> ADP + Pi

This reaction can be reversed when energy is released from glucose during respiration and is used to restore the high energy bond.

ADP + Pi —————–> ATP

Question 31

Phosphorylation

Answer 31

Addition of a phosphate

eg. ADP + Pi —-> ATP

(Also the phosphorylation of glucose in glycolysis)

Question 32

Glycolysis

Answer 32

Occurs in the cytoplasm.

Results in the breakdown of glucose into 2 x molecules of pyruvate, with a net gain of 2 ATP.

It is enzyme controlled and does not require oxygen.

Question 33

Energy investment phase

Answer 33

2 ATP are used to phosphorylate glucose, making it more reactive.

Question 34

Energy payoff phase

Answer 34

Phosphorylated glucose splits to form 2 molecules of pyruvate, which generates 4 ATP.

Net ATP gain from glycolysis = 2ATP

Question 35

Dehydrogenase enzymes

Answer 35

Remove hydrogen (H+ and e-) and use them to reduce coenzyme NAD to NADH.

Happens in glycolysis and the citric acid cycle.

Question 36

NAD

Answer 36

A coenzyme molecule that is reduced when it combines with hydrogen to become NADH.

Carries hydrogen to the electron transport chain.

Question 37

Matrix (mitochondrion)

Answer 37

The central jelly-like part of the mitochondrion.

The citric acid cycle happens here.

Question 38

Acetyl coenzyme A

Answer 38

Pyruvate loses carbon (as carbon dioxide) to become acetyl, which combines with coenzyme A so that it can enter the citric acid cycle.

This is known as the link reaction.

It happens in the mitochondrion.

Question 39

Citric acid cycle

Answer 39

One of the metabolic pathways of respiration which occurs in the matrix of the mitochondrion.

The acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate, which is gradually converted back to oxaloacetate in a series of enzyme controlled steps.

Carbon dioxide and ATP are generated, and hydrogen is removed by dehydrogenase enzymes creating NADH.

Question 40

Electron transport chain

Answer 40

A group of protein molecules in the inner mitochondrial membrane, which act as electron acceptors and carriers.

They work with the enzyme ATP synthase in a metabolic pathway which generates large quantities of ATP.

Hydrogen is unloaded from NADH and splits into H+ (protons) and e- (electrons).

The electrons pass along the electron transport chain and drive the pumping of protons across the membrane, into the intermembrane space.

Question 41

ATP synthase

Answer 41

A complex of protein molecules in the inner mitochondrial membrane, which rotates to generate ATP from ADP + Pi.

It is driven by the return flow of protons from the intermembrane space back to the matrix of the mitochondrion.

Question 42

Concentration gradient

Answer 42

A difference in concentration between 2 areas.

A high concentration of protons is maintained by pumping them into the intermembrane space, resulting in a return flow of protons back to an area of low concentration through ATP synthase.