Lecture 7 - Carbohydrate Metabolism

What is the primary source of energy for cells?

Glucose

How do carbohydrates spare protein in the body?

They prevent the breakdown of protein for energy, allowing protein to focus on building, repairing and maintaining tissues.

What condition do carbohydrates prevent when they are limited?

Ketosis: when carbohydrates are limited, fats are broken down for energy which leads to the production of ketone bodies and makes the body become slightly acidic.

What are the three fates of glucose in a cell?

1) Enters glycogenesis for energy storage, 2) Enters glycolysis for energy production, 3) Enters hexose monophosphate shunt for biogenesis.

What is glycolysis?

A metabolic pathway that converts glucose into pyruvate, producing energy in the form of ATP.

What is gluconeogenesis?

The pathway that synthesizes glucose from non-carbohydrate precursors, active during fasting.

What is glycogenolysis?

The process of breaking down glycogen into glucose for energy.

What is the role of glycogenin in glycogenesis?

Glycogenin acts as a primer to attach glucose molecules and initiate glycogen synthesis.

What enzyme is the first committed step in glycolysis?

Phosphofructokinase

What is the net energy yield from one glucose molecule during glycolysis?

2 ATP and 2 NADH (equivalent to ~8 ATP)

What happens to pyruvate in anaerobic conditions?

It is converted into lactate.

What is the Cori Cycle?

The process where lactate produced in muscles is transported to the liver and converted back to glucose.

What is the hexose monophosphate shunt used for?

To produce NADPH and ribose for nucleotide synthesis.

What are the two types of phosphorylation that produce energy in the cell?

1) Substrate-level phosphorylation, 2) Oxidative phosphorylation.

What is the role of the Pyruvate Dehydrogenase Complex?

It converts pyruvate into acetyl-CoA, linking glycolysis to the Krebs Cycle.

What is the total theoretical energy yield from one glucose molecule?

38 ATP

What is the significance of NADH in cellular respiration?

NADH carries electrons to the electron transport chain, contributing to ATP production.

What is the main difference between aerobic and anaerobic glycolysis?

Aerobic glycolysis produces pyruvate that enters the Krebs Cycle, while anaerobic glycolysis converts pyruvate to lactate.

How does insulin affect carbohydrate metabolism?

Insulin promotes glycogenesis and lowers blood glucose levels.

How does glucagon affect carbohydrate metabolism?

Glucagon stimulates glycogenolysis and gluconeogenesis, raising blood glucose levels.

What is the role of lactic acid in anaerobic metabolism?

Lactic acid allows glycolysis to continue by regenerating NAD+.

What is the primary function of the hexose monophosphate shunt?

To generate NADPH for biosynthetic reactions and ribose for nucleotide synthesis.

6 processes in carbohydrate metabolism

Glycogenolysis, gluconeogenesis, glycolysis, glycogenesis, kreb's cycle, hexose monophosphate shunt

Glycogenolysis: Catabolic or anabolic

Catabolic

Gluconeogenesis: Catabolic or anabolic

Anabolic

Glycolysis: Catabolic or anabolic

Catabolic

Glycogenesis: Catabolic or anabolic

Anabolic

Kreb's Cycle: Catabolic or anabolic

Both

Hexose monophosphate shunt (oxidative phase): Catabolic or anabolic

Catabolic

Glycogenesis: Liver

Converts glucose to G6P using GLUCOKINASE

Glycogenesis: Muscle

Converts glucose to G6P using HEXOKINASE

Glycogenesis: What inhibits hexokinase and why?

G6P inhibits hexokinase, only the liver can put it back into the blood stream, not muscle. What the muscle takes, it keeps.

Glycogenesis: What happens after glucose is converted to G6P

G6P is converted to G1P

Glycogenesis: What converts G61 to be added to glucose and how does it do it?

GLYCOGEN SYNTHASE. Adds glucose one at a time to mkae long term energy resevoir.

Glycogenesis: What is insulins role?

Activates hexokinase, glucokinase and glycogen synthase

Glycogenesis: What is glyocogenin?

Serves as a scaffold for glucose to attach and build glycogen. It attaches itself to glucose before glycogen synthase takes over to add glucose to the glycogen store.

Glycogenesis: How many glucose molecules can be added to a glycogen store

30,000+

Glycogenesis: Does adding glucose to the glycogen store require ATP. T or F

True, not in the making of glycogen but in the first step of converting glucose to G6P to get into the cell

Glycogenesis: Main enzymes and hormones

Hexokinase, glucokinase, insulin, glycogen synthase, glycogenin

Glycogenolysis: What does glycogen phosphorylase do?

Breaks down a-1,4 glycosidic bonds to get free glucose

Glycogenolysis: What hormone activates glycogen phosphorylase?

GLUCAGON

Glycogenolysis: Why would our bodies need to do this?

Need to tap into stored energy due to no CHO, fasted state

Glycogenolysis: What in the liver can convert G6P back to glucose once its been release from glycogen stores by removing a phosphate?

Glucose-6-phosphatase, ONLY LIVER

Why are glucagon and insulin never high together

They are doing opposite things, insulin puts glucose into storage and glucagon takes it out

Glycogenolysis: Main enzymes and hormones

Glycogen phosphorylase, glucagon, glucose-6-phosphatase

Glycogensis/Glycogenolysis

High blood sugar, high insulin. Low blood sugar, high glucagon

LIVER IS THE ONLY TISSUE THAT CAN RELEASE GLUCOSE BACK INTO THE BLOOD. T or F

True

Where is energy produced in a cell?

Substrate-level phosphorylation (mitochondria or cytoplasm) and Oxidative phosphorylation (mitochondria)

Glycolysis: location

Cytoplasm

Glycogenolysis: Anaerobic or aerobic

Both

Glycogenolysis: Why is it the only way RBCs get ATP

No mitochondria

Glycogenolysis: End point

Pyruvate

Glycolysis: What converts glucose to G6P

Glucokinase/hexokinase

Glycolysis: What can inhibit phosphofructokinase

Glucagon and ATP can inhibit if it is not needed

Glycolysis: How many ATPs to start

2 ATP

Glycolysis: How many NADH created

1 NADH for ETC (x2)

Glycolysis: Where does pyruvate go

Aerobic: Kreb's. Anaerobic: Fermentation to lactate

Glycolysis: Net energy

2 NADH + 2 ATP = 8 ATP

Anaerobic Lactic Acid production: Occurs where and why

In muscle and RBCs during prolonged exercise

Anaerobic Lactic Acid production: What does it regenerate to help

NAD+ so glycolysis can continue

Anaerobic Lactic Acid production: Net ATP

2 ATP

Anaerobic ethanol production: Yeast breaks down pyruvate into what

CO2 and ethanol

Anaerobic ethanol production: What does it regenerate to help

NAD+ so glycolysis can continue

Cori Cycle: Occurs where and why

Anaerobic in muscle to produce lactate

Cori Cycle: The muscle can't use lactate, where does it go

Back to the liver for gluconeogenesis to go from pyruvate to glucose

Cori Cycle: Energy consumption for 2 molecules of lactate

6 ATP

Cori Cycle: Why is it a short term and a big energy defecit

Uses 6 ATP to generate 2 ATP

Hexose monophosphate shunt: Location

Cytoplasm

Hexose monophosphate shunt: Important for creating what

NADPH for ribose synthesis

Hexose monophosphate shunt: What is the step that commits glucose to the oxidative phase

Glucose-6-phosphate dehydrogenase

Hexose monophosphate shunt: Why is NADPH production important

Support fatty acid biosynthesis and oxidant defense system

Hexose monophosphate shunt: What intermediates does it go to to support nucleotide synthesis (RNA/DNA)

Ribose-5-phosphate

Hexose monophosphate shunt: Why do all cells use the non-oxidative phase

Need it for nucleotides

Hexose monophosphate shunt: What happens if theres too much NADPH

Feeds back to inhibit Glucose-6-phosphate dehydrogenase since it is not needed

Hexose monophosphate shunt: Oxidative phase catabolic or anabolic

Catabolic: losing CO2 and going from 6C to 5C

Hexose monophosphate shunt: Non-oxidative phase catabolic or anabolic

Neither, just structure rearrangement

Pyruvate dehydrogenase: Converts pyruvate to what

Acetyl-CoA

Pyruvate dehydrogenase: How many NADH generated for ETC

1 NADH

Pyruvate dehydrogenase: 4 B vitamin cofactors (micronutrients)

Thiamine, niacin, riboflavin, pantothenic acid

Pyruvate dehydrogenase: How many ATP yield

1 NADH = 3 ATP (x2) = 6 ATP

Kreb's Cycle: Location

Mitochondrial matrix

Kreb's Cycle: Purpose

Final metabolic pathway for products of protein, lipids, carbs

Kreb's Cycle: What does the cell need if it wants to burn a lot of Acetyl-CoA

Matching amount of oxaloacetate

Kreb's Cycle: What does Pyruvate carboxylase do

Convert pyruvate to oxaloacetate for balance

Kreb's Cycle: What activates Pyruvate carboxylase

High amount of Acetyl-CoA

Kreb's Cycle: At what 3 steps can amino acids enter at

Alpha-ketoglutarate, succinyl-CoA, oxaloacetate

Kreb's Cycle: Why does the body try to prevent amino acids from entering

To form proteins

Kreb's Cycle: ATP yield

3 NADH + 1 FADH2 + 1 GTP = 12 ATP

Amount of energy yield from each process

Glycolysis = 8 ATP (2 ATP and 2 NADH)

Pyruvate dehydrogenase = 6 ATP (1 NADH x2)

Kreb's Cycle = 24 ATP (3 NADH + 1 FADH2 + 1 GTP x2)

Gluconeogenesis: When is it active

When glucose is needed (starvation)

Gluconeogenesis: Where is it active

Liver, can be kidney during starvation

Gluconeogenesis: Why is not active in muscle and adipose?

They lack the enzymes needed

Gluconeogenesis: Which process is it the reverse of

Glycolysis

What are the 3 steps in glycolysis that are unidirectional?

Glucokinase/hexokinase, phosphofructokinase, pyruvate kate

Kreb's Cycle: Main enzymes

Pyruvate carboxylase

Gluconeogenesis: Enzymes that bypass glycolysis' unidirectional steps

Glucose-6-phosphatase, frucose-1,6-bisphosphate, pyruvate carboxylase + PEP carboxykinase

Gluconeogenesis: What does Pyruvate translocase do

Bring pyruvate into the mitochondria when it is needed

Gluconeogenesis: Pyruvate needs to get out of mitochondria, what form does it need to go into

Oxaloacetate and then malate

Gluconeogenesis: What converts pyruvate to oxaloacetate

PYRUVATE CARBOXYLASE

Gluconeogenesis: What converts oxaloacetate to malate

MALATE DEHYDROGENASE (mitochondria and cytoplasm)