The Cell as a Factory

Question 1

What is the general formula of Carbohydrates and what are their function?

Answer 1

Cn(H2O)n.

• Source of stored energy.
• Transport stored energy.
• Act as carbon skeletons for many other molecules.

Question 2

What are monosaccharides and what are the 2 types?

Answer 2

Monosaccharides are simple sugars. They are monomers from which larger CHO’s can be constructed. All living cells contain the monosaccharide glucose. They bind together in condensation reactions to form glycosidic linkages. Can be pentoses (5 carbons) or hexoses (6 carbons, structural isomers).

Question 3

What are the 2 glucose forms?

Answer 3

Straight chain or ring form. Ring form is more common and more stable, and exists as alpha or beta glucose which can interconvert.

Question 4

What are disaccharides?

Answer 4

2 simple sugars linked by covalent bonds. Most familiar is sucrose.

Question 5

What are oligosaccharides?

Answer 5

3-20 monosaccharides. They may include other functional groups and are often covalently boned to proteins and lipids on cell surfaces and act as recognition signals.

Question 6

What are polysaccharides?

Answer 6

Hundreds or thousands of monosaccharides. Examples are starch, glycogen and cellulose.

Question 7

What are the 4 main types of lipids and what do they do?

Answer 7

1. Fats and oils which store energy.
2. Phospholipids which have a structural role in cell membranes.
3. Carotenoids and chlorophylls which capture light energy in plants.
4. Steroids and modified fatty acids which act as hormones and vitamins.

Question 8

What are fats and oils composed of?

Answer 8

Fats and oils are triglycerides composed of fatty acids and glycerol. Glycerol has 3 OH groups and fatty acids are non polar hydrocarbons with a carboxyl group. The carboxyl bonds form with the hydroxyls of the glycerol molecule in an ester linkage.

Question 9

What does amphipathic mean?

Answer 9

Fatty acids have opposing chemical properties. One end is strongly hydrophilic (when carboxyl group ionises to form -COO) and the other end is strongly hydrophobic.

Question 10

What are phospholipids composed of?

Answer 10

Fatty acids bound to glycerol, a phosphate group replaces one fatty acid. The phosphate group is the head which is hydrophilic and the tails are fatty acid chains which are hydrophobic. Phospholipids are amphipathic.

Question 11

Is conversion of ADP to ATP exergonic or endergonic?

Answer 11

Endergonic. Energy is then released when ATP is broken down to ADO + Pi.

Question 12

What happens in the processes of glycolysis, cellular respiration and fermentation?

Answer 12

Glycolysis - Glucose is converted to pyruvate.
Cellular respiration - aerobic and converts pyruvate to water, CO2 an ATP. Complete oxidation.
Fermentation - Anaerobic and converts pyruvate to lactic acid or ethanol, CO2 and ATP. Incomplete oxidation.

Question 13

If oxygen is present,, what are the 3 pathways that follow glycolysis?

Answer 13

1. Pyruvate oxidation.
2. Citric acid cycle.
3. Electron transport chain.

Question 14

The reactant that becomes reduced it the oxidising/reducing agent?

Answer 14

Oxidising.

Question 15

What is NAD+ and what are its 2 forms?

Answer 15

It is a coenzyme, a key electron carrier in redox reactions. 2 forms are NAD+ (oxidised) or NADH (reduced).

Question 16

In eukaryotes where do the following processes take place in the cell:

a) Glycolysis and fermentation.
b) Respiratory chain
c) Citric acid cycle and pyruvate oxidation.

Answer 16

a) Glycolysis and Fermentation take place in the cytoplasm.
b) The respiratory chain takes place in the inner membrane of the mitochondria.
c) Citric acid cycle and pyruvate oxidation take place in the matrix of the mitochondria.

Question 17

In prokaryotes, where do the following processes take place in the cell:

a) Glycolysis, fermentation, citric acid cycle.
b) Pyruvate oxidation and respiratory chain.

Answer 17

a) Glycolysis, fermentation and citric acid cycle take place in the cytoplasm.
b) Pyruvate oxidation and respiratory chain take place on the plasma membrane.

Question 18

Where does glycolysis take place?

Answer 18

In the cytosol, the aqueous component of cytoplasm.

Question 19

In glycolysis, which enzyme-catalysed reactions are energy-investing and which are energy-harvesting?

Answer 19

1-5 are energy-investing and require ATP, and 6-10 are energy-harvesting and they yield NADH and ATP.

Question 20

What is produced by the end of glycolysis?

Answer 20

• 2 molecules of pyruvate.
• 2 molecules of ATP.
• 2 molecules of NADH.

Question 21

What is substrate-level phosphorylation?

Answer 21

The enzyme-catalysed transfer of a phosphate group from a donor to ADP to form ATP.

Question 22

What are the 3 main things that happen during pyruvate oxidation?

Answer 22

1. Pyruvate is oxidised to acetate and CO2 is released.
2. NAD+ is reduced to NADH.
3. Some energy is stored by combining acetate with CoA to form acetyl CoA.

Question 23

What are the inputs for the citric acid cycle?

Answer 23

Acetyl CoA, water and electron carriers NAD+, FAD and GDP.

Question 24

What is energy release in the citric acid cycle captured by?

Answer 24

ADP and electron carriers NAD+, FAD and GDP.

Question 25

What are the outputs of the citric acid cycle?

Answer 25

CO2, reduced electron carriers, and GTP which converts ADP to ATP.

Question 26

What must happen to the reduced electron carriers before they can be used again?

Answer 26

They must be re-oxidised.

Question 27

What is oxidative phosphorylation and what are the 2 stages?

Answer 27

ATP is synthesised by re-oxidation of electron carriers in the presence of O2. The 2 stages are the electron transport chain and chemiosmosis.

Question 28

Why does the electron transport chain have so many steps and not just 1?

Answer 28

Too much free energy would be released at once and could not be harvested by the cell. In a series of reactions, each releases a small amount of energy that can be captured by an endergonic reaction.

Question 29

What happens when protons are actively transported along the electron transport chain?

Answer 29

They accumulate in the inter membrane space and create a concentration gradient and charge difference - POTENTIAL ENERGY. This proton-motive force then drives the protons back across the membrane.

Question 30

What is chemiosmosis?

Answer 30

This is when protons diffuse back into the mitochondria through ATP synthase, a channel protein. Diffusion is coupled to ATP synthase. This creates ATP which immediately leave the mitochondria to keep the concentration low.

Question 31

How is the proton gradient maintained during the respiratory chain?

Answer 31

Electron transport and proton pumping.

Question 32

How can ATP synthesis be uncoupled and what is an example?

Answer 32

It can be uncoupled if a different H+ diffusion channel is inserted into the mitochondrial membrane so that the energy is lost as heat. An example is the uncoupling protein thermogenic which occurs in human infants and hibernating animals. H+ is released as heat instead of coupled to ATP synthesis.

Question 33

What are the 2 subunits of ATP synthase?

Answer 33

1. F0 subunit - transmembrane.

2. F1 subunit - projects into the mitochondrial matrix to expose active sites for ATP synthesis.

Question 34

Where does lactic acid fermentation occur and what happens?

Answer 34

In microorganisms and some muscle cells. Pyruvate is the electron acceptor and lactate is the product that can build up.

Question 35

Where does alcoholic fermentation occur and what happens?

Answer 35

In yeast and some plant cells. Requires 2 enzymes to metabolise pyruvate to alcohol. Acetaldehyde is reduced by NADH and H+ producing NAD+ and glycolysis continues.

Question 36

How much ATP is produced in Glycolysis and fermentation vs Glycolysis and cellular respiration?

Answer 36

Glycolysis and fermentation = 2 ATP.

Glycolysis and cellular respiration = around 32 ATP.

Question 37

How are metabolic pathways interrelated and regulated?

Answer 37

• An interchange of molecules occurs between metabolic pathways.
• Pathways are interrelated by shared substances.
• Pathways are regulated by enzyme inhibitors.

Question 38

What are catabolic interconversions of metabolic pathways?

Answer 38

1. Polysaccharides are hydrolysed to glucose which enters glycolysis and cellular respiration.
2. Lipids are broken down into glycerol (which forms DAP) and fatty acids (which form acetyl CoA).
3. Proteins are hydrolysed to amino acids which feed into glycolysis or the citric acid cycle.

Question 39

What are anabolic interconversions of metabolic pathways (Gluconeogenesis)?

Answer 39

Gluconeogenesis is when glucose is formed from the citric acid cycle and glycolysis intermediates

Question 40

How are catabolism and anabolism integrated?

Answer 40

1. Negative and positive feedback controls.

2. Concentrations of biochemical molecules remain constant (e.g. glucose concentration in the blood).

Question 41

What is the main allosteric regulation control point in glycolysis?

Answer 41

Phosphofructokinase which is allosterically inhibited by ATP.

Question 42

What is the main allosteric regulation control point in the citric acid cycle?

Answer 42

Isocitrate dehydrogenase which is inhibited by NADH + H+, and ATP.

Question 43

What are 2 other control points if ATP levels get too high?

Answer 43

• Accumulation of citrate diverts acetyl CoA to fatty acid synthesis for storage.
• Fatty acids may be metabolised later to produce more acetyl CoA.