3. Carbohydrates

Question 1

Explain the linkages in glycogen, starch, cellulose, and lactose.

Answer 1

glycogen - animal energy storage, alpha linkage
starch - plant energy storage, alpha linkage
cellulose - plant cell wall, beta linkage (we cannot digest beta linkages)
lactose is also a beta linkage and one exception for humans as we developed lactase enzyme

Question 2

t or f, cellular respiration: glucose is oxidized into CO2 and ATP in four steps: glycolysis, pyruvate dehydrogenase complex, Krebs cycle, and the electron transport chain.

Answer 2

true

Question 3

What is NAD+ and FAD?

Answer 3

These are electron carriers that facilitate cellular respiration by reducing into NADH and FADH2

Question 4

Where does the each step in glucose oxidation occur and explain the oxygen involvement.

Answer 4

glycolysis - cytoplasm - no oxygen needed
PDC and Krebs - mitochondrial matrix and do not use oxygen, but require oxygen to occur
ETC - inner mitochondrial membrane. Uses oxygen at end of chain.

Question 5

glycolysis, explain the enzymes hexokinase, PFK, and pyruvate kinase. What is the committed step of glycolysis?

Answer 5

hexokinase starts glycolysis by converting glucose to G-6-P which then changes into F-6-P
PFK converts F-6-P into F-1,6-BP. This is the committed step of glycolysis.
After several mini steps, pyruvate kinase converts 2 PEP into 2 pyruvate compounds.

note: ATP negatively allosterically regulates PFK

Question 6

What are the products of glycolysis?

Answer 6

2 ATP, 2NADH, and 2 pyruvate molecules

Question 7

What is fermentation?

Answer 7

When there is a lack of oxygen, oxidation of glucose cannot go to the PDC. To allow glycolysis to continue in the absence of oxygen, fermentation allows the pyruvate compounds created by glycolysis to oxidize NADH and regenerate NAD+.

Question 8

Compare fermentation in yeast to humans.

Answer 8

In yeast, fermentation creates ethanol. In humans, fermentation creates lactate which explains why our legs burn during exercise.

Question 9

What occurs at the pyruvate dehydrogenase complex? What are the products?

Answer 9

In the mitochondrial matrix, the PDC converts pyruvate to an acetyl unit. The acetyl unit is then joined with coenzyme-A to form Acetyl-coA which enters the Krebs cycle.

1CO2, 1NADH, 1 Acetyl-coA (per pyruvate)

Question 10

What is a prosthetic group?

Answer 10

A tightly bound or covalently bound cofactor. PDC has thiamine (vitamin B1) as its prosthetic group.

Question 11

Explain the general process of the Krebs cycle.

Answer 11

Acetyl-coA drops combines its 2 carbon sub-unit with oxaloacetate to start the Kreb cycle. Oxaloacetate goes through a double oxidative decarboxylation process to eventually regenerate itself.

oxaloacetate –> citrate –> isocitrate –> etc etc –>

Question 12

What does the Kreb cycle produce per acetyl-coA?

Answer 12

2CO2, 3NADH, 1GTP, 1FADH2

Question 13

What is oxidative phosphorylation?

Answer 13

Oxidative phosphorylation is the process of oxidation the high-energy electron carriers (NADH and FADH2) coupled with the phosphorylation of ADP to create ATP.

Question 14

The electron transport chain, within the inner mitochondrial membrane, is composed of 5 enzymes. What are cytochromes?

Answer 14

Three of these enzymes (1, 3, and 5) are larger enzymes, embedded in the membrane and contain a heme group. These are called cytochromes. These are responsible for pumping H+ into the inter-membrane space. Then ATP Synthase utilizes this proton gradient to transfer phosphate onto ADP.

Question 15

Name the members of the electron transport chain.

Answer 15

NADH drops its electrons onto the first protein called NADH dehydrogenase (coenzyme Q reductase).

2. Coenzyme Q or ubiquinone
3. Cytochrome C reductase
4. Cytochrome C
5. Cytochrome C oxidase

Cytochrome C oxidase then transfers its electrons to oxygen to produce water.

This is the sole purpose we breath

Question 16

Hpw much ATP does NADH from the Kreb cycle and the PDC produce?

Answer 16

NADH from these systems places its electrons on NADH dehydrogenase resulting in 10 protons being pumped. ATP Synthase requires 4 H+ for 1 ATP. Thus, these NADH produce 2.5 ATP each.

Question 17

How much ATP does FADH2 and NADH from glycolysis produce?

Answer 17

NADH from glycolysis needs to be shuttled into the mitochondria from the cytoplasm. This shuttle (glycerol phosphate shuttle) delivers NADH to coenzyme Q. FADH2 also reduces Coenzyme Q directly. By missing the first enzyme, they only pump 6 protons out resulting in 1.5 ATP per molecule.

Question 18

In total, how much ATP is produced from 1 glucose molecule? Break it down.

Answer 18

glycolysis - 2 ATP, 2NADH
PDC - 2NADH
Kreb cycle - 6 NADH, 2FADH2, 2 GTP

8 NADH = 80 H+ / 4 = 20 ATP 
2 FADH2 = 12 H+ / 4 = 3 ATP 
2 NADH (gly) = 12 H+ / 4 = 3 ATP 
glycolysis = 2 ATP 
Kreb cycle = 2 GTP 

add it up = 30 ATP in humans
prokaryotes actually produce 32 per glucose

Question 19

What is gluconeogenesis? Where does it occur?

Answer 19

Gluconeogenesis is the process of creating glucose from metabolic intermediates (pyruvate, lactate, etc.) when glycogen stores and free glucose is low. It is essentially glycolysis in reverse.
It occurs in the liver mainly.

Question 20

Explain the enzymes used in gluconeogenesis.

Answer 20

pyruvate --> oxaloacetate: pyruvate decarboxylase
oxaloacetate --> PEP: PEP carboxykinase
many reactions
F-16-Bp --> F-6-P: F-16-biphosphatase
G-6P --> glucose: G-6-phosphatase

most enzymes are the opposite of the glycolysis enzymes

Question 21

What effect does AMP and fructose-2,6,bP have on glycolysis and gluconeogenesis?

Answer 21

In these pathways, the committed step is regulated (PFK and F-1,6-bP)

AMP and fructose-2,6,bP stimulate PFK (i.e. glucose breakdown) and inhibit F-1,6-bP (i.e. glucose production)

Question 22

How does insulin effect fructose-2,6,bP and blood glucose levels?

Answer 22

After a sugary meal, insulin is secreted to help reduce blood glucose levels. Thus, insulin increases the levels of fructose-2,6,bP which serve to stimulate PFK and therefore glucose catabolism. fructose-2,6,bP will also inhibit gluconeogenesis.

Question 23

Where is glycogen found?

Answer 23

muscle and liver cells

Question 24

Glucose –> G-6-P –> G-1-P –> UDP-glucose –> glycogen

glycogen –> G-1-P –> G-6P

Explain the enzymes of glycogenesis and glycogenlysis

Answer 24

G-6-P –> G-1-P: phosphoglucomutase (PGM)
G-1-P –> UDP-glucose: UDP-G-pyrophophorylase
UDP-glucose –> glycogen: glycogen synthase

glycogen –> G-1-P: glycogen phosphorylase

Question 25

Why do muscle cells not contain G-6-phosphatase?

Answer 25

G-6-phosphatase converts G-6-P into glucose. Muscle cells do not need to secrete glucose. Leaving it as G-6-P retains the material in the muscle cell, which can enter glycolysis for respiration, or re-enter glycogenesis.

Question 26

The pentose phosphate pathway (PPP) shunts G-6-P out of glycolysis to produce NADPH and ribose-5-P. Explain these molecules.

Answer 26

NADPH –> reducing agent in anabolic processes (fatty acid synthesis) and removes ROS

ribose-5-P –> makes nucleotides

Question 27

What is G-6-P dehydrogenase (G6PDH)?

Answer 27

G-6-P dehydrogenase is the enzyme that initiates the pentose phosphate pathway.