Non-Aerobic Carbohydrate Metabolism

Question 1

the breakdown of complex molecules in living organisms to form simpler ones, together with the release of energy; destructive metabolism.

Answer 1

catabolism

Question 2

the synthesis of complex molecules in living organisms from simpler ones together with the storage of energy; constructive metabolism.

Answer 2

anabolism

Question 3

What are the two basic pathways that glucose is used to provide energy?

Answer 3

1. substrate level phosphorylation
2. oxidative phosphorylation

Question 4

Process in which a phosphate group of a substrate is transfered to ADP to make ATP during glycolysis

takes place in the cytoplasm during glycolysis and in the mitochondria during Kreb’s cycle

Answer 4

substrate level phosphorylation

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Question 5

the addition of phosphate groups is called

Answer 5

phosphorylation

Question 6

the process of forming ATP via the transfer of electrons in the ETC

Answer 6

oxidative phosphorylation

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Question 7

What is the name of this process?

Answer 7

oxidative phosphorylation

Question 8

What are the two oxidizing agents used in oxidative phosphorylation?

Answer 8

NADH
FADH₂

Remember: these two oxidizing agents are also coenzymes

The role of reduced NAD and FAD is to provide electrons for the electron transport chain. In the Kreb’s cycle, they are reduced to NADH and FADH2. The extra hydrogen ions in these coenzymes dissassociate and are actively transported across the inner mitochondrial membrane. The electrons are donated to the first and second electron carrier proteins in the electron transport chain. These electrons move down the transport chain, losing free energy as they move. It is this energy that is used to actively transport the hydrogen ions across the inner mitochondrial membrane!

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Question 9

What are two ways in which sugar can enter the bloodstream?

Answer 9

1. Absorption from small intestine and liver cells
2. Cells in the renal cortex produce it via gluconeogenesis or glycogenolysis

Question 10

What family of receptors help glucose diffuse through the plasma membrane?

Answer 10

GLUT family

Question 11

Why can’t glucose diffuse through the cell membrane by itself

Answer 11

Glucose is too polar, thus it must use GLUT receptors to transport it across the plasma membrane

Question 12

Name the glucose transport receptor

expressed throughoutbody and is responsible for constant low-level baseline glucose intake

Answer 12

GLUT1

Question 13

expressed by liver, pancreatic beta, and some kidney cells. It is a bidirectional transporter that allows glucose to be transported both in and out of the cell. Crucial for gluconeogenesis

Answer 13

GLUT2

Question 14

primarily expressed in neurons and placenta. High-affinity transporter (can transport glucose even when blood glucose levels are low).

Answer 14

GLUT3

Question 15

expressed in skeltetal and cardiac muscle and adipose tssues. Regulated by insulin. Main role is to store glucose in skeleta, cardiac, and adipose tissues when there is surplus glucose levels in blood. Implicated in type 2 diabetes

Answer 15

GLUT4

Question 16

the initial metabolic pathway in the metabolism of carbohydrates that can occur with or without oxygen

Answer 16

glycolysis

Glycolysis is the major pathway of glucose metabolism and occurs in the cytosol of all cells. It can occur aerobically or anaerobically depending on whether oxygen is available. This is clinically significant because oxidation of glucose under aerobic conditions results in 32 mol of ATP per mol of glucose. However, under anaerobic conditions, only 2 mol of ATP can be produced
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Question 17

expresed in skeletal and cardiac muscle, and adipose tissues. Regulatied by insulin. Main job is storing glucose

Answer 17

GLUT4

Question 18

where does glycolysis take place?

Answer 18

the cytosol

Question 19

What are the major outcomes of glycolysis?

Answer 19

• glucose is broken down to produce 2 molecules of pyruvate
• NAD+ gets converted to NADH
• ATP production

Question 20

serves as a means of energy production in cells that cannot produce adequate energy through oxidative phosphorylation. In poorly oxygenated tissue, this process produces 2 ATP by shunting pyruvate away from mitochondria and through the lactate dehydrogenase reaction

Answer 20

anaerobic glycolysis

Question 21

What are the products of anaeorobic glycolysis?

Answer 21

2 ATP + lactic acid (animals) or ethanol (yeast)

Question 22

Why does fermentation occur in anaerobic glycolysis?

Answer 22

NADH needs to be converted to NAD+ for glycolysis to continue, but in the abscence of oxygen, fermentation provides a way for NAD+ to be regenerated

Question 23

Describe ethanol fermentation

Answer 23

This is used by yeast and consists of 2 steps:
1. Pyruvate loses a carboxylic acid functional group, becoming an acetalaldehyde and carbon dioxide (this step is catylyzed by pyruvate decarboxylase)
2. Alcohol dehydrogenase turns acetaladehyde into an ethanol in a reaction coupled to the conversion of NADH to NAD+

Question 24

Describe the steps in lactic acid fermentation

Answer 24

Pyruvate is converted to lactate by lactate dehydrogenase in a reaction used to convert NADH to NAD+. This process takes place in human muscle cells.

Question 25

Where does gluconeogenesis occur?

Answer 25

The liver (50-60%), kidneys (40%) and to some extent in the adrenal cortex and intestines

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the liver regulates blood glucose levels so ensuring an adequate glucose supply is throughout the body’s tissues

Question 26

List the ways in which glycolysis is different from gluconeogenesis

Answer 26

• The main difference between gycolysis and gluconeogenesis is that glycolysis is involved in the glucose catabolism whereas gluconeogenesis is involved in the glucose anabolism.
• Gluconeogenesis STARTS with pyruvate
• The final step of glycolysis is skipped by gluconeogenesis
• Early stages of glycolysis where phosphate groups are added are bypassed

Question 27

What is the purpose of gluconeogenesis?

Answer 27

To provide a ready source of glucose to the body - particularly for liver cells use - when blood glucose levels are low

Question 28

Why are the early stages of glycolysis where the phosphate groups are added bypassed in gluconeogenesis?

Answer 28

Because 1.) they are irreversible and 2.) involves ATP investment. It would not make sense for gluconeogenesis to reverse these steps bc doing so would mean creating ATP, which is the job of ATP synthase in the ETC. Instead, gluconeogenesis bypasses these steps by catylyzing a hydrolysis reactrion, splitting off a P_i from the carbohydrate

Question 29

Why is the final stage of glycolysis bypassed in gluconeogenesis?

Answer 29

1.) it is irreversible
2.) The cell must avoid a futile cycle in which pyruvate from glycolysis is immiediately converted back to PEP. This is why gluconeogenesis has a two-step pathway split up between the mitochondria and the cytoplasm

Question 30

Fill in the blank

Each glycogen molecule is formed around a core formed by the protein ____, which is the base for glycogen synthesis. This protein also helps catylyze the buildup of the first 8 glucose molecules, after which glycogen synthase can take over

Answer 30

Glycogenin

Question 31

Fill in the blanks

Glycogen molecules are linked together by ____ within each branch, while ____ linkages form seperate branches

Answer 31

Glycogen molecules are linked together by 𝝰(1–>4) within each branch, while 𝜶(1–>6) linkages form seperate branches

Question 32

The synthesis of glycogen

Answer 32

Glycogenesis

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Question 33

Name the metabolic pathway

Process where glucose is shunted off from glycolysis/gluconeogenesis pathway and ‘marked’ for [insert process here] by moving the phosphate group

Answer 33

Glycogenesis

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Question 34

Name the enzyme

During glycogenesis, this enzyme forms the 𝝰(1–>4) linkages between molecules of glucose to form the growing glycogen strand. It does this by catalyses the incorporation of uridine diphosphate-glucose (UDP-glucose) into glycogen in skeletal muscle

Answer 34

glycogen synthase

Question 35

Name the enzyme

Forms new branches of 𝜶(1–>6) linkages

Answer 35

glycogen-branching enzyme

Question 36

Name the metabolic pathway

The biochemical pathway in which glycogen breaks down into glucose-1-phosphate and glucose. The reaction takes place in the hepatocytes and the myocytes. The process is under the regulation of two key enzymes: phosphorylase kinase and glycogen phosphorylase.

Answer 36

glycogenolysis

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Throughough explanation video

Question 37

Name the enzyme (fill in the blank)

Glycogen phorylase, like ____ , only works on ⍺(1–>4) linkages

Answer 37

Glycogen synthase

Question 38

What two enzymes deal with α(1–>6) linkages in glycogen metabolic pathways?

Answer 38

1. Glycogen branching enzyme and
2. glycogen debranching enzyme

Question 39

Name the metabolic process

Shunts glucose-6-phosphate away from glycolysis/gluconeogenesis pathway and uses it to do other structurally important things. Particularly, it converts NADP+ to NADPH and converts glucose-6-phosphate into ribose 5-phosphate

Answer 39

pentose phosphate pathway

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Question 40

This product serves the functions of a.) being a reducing agent needed to synthezize lipids and nucleic acids and b.) helps protect against damage from reactive oxygen synthesis by regenerating the antioxidant glutathione from its oxidative form

Answer 40

NADPH

Question 41

Name the phase and the pathway

Oxidizes a glucose 6-phosphate into a ribose 6-phosphate while in the process generated two NADPH molecules, a carbon dioxide and 2 H+ ions.

Answer 41

Oxidative phase of the pentose-phosphate pathway

Question 42

Name the phase and the pathway

Links the glycolytic pathway to the ____ pathway and it allows our cells a way to break down ribose molecules ingested into our body. This phase uses several important enzymes, including phosphopentose isomerase, phosphopentose epimerase, transketolase and transaldolase.

Answer 42

Non-oxidative phase of the pentose phosphate pathway

Question 43

Glycolyisis is upregulalted when ____ and downregulated when ____

Answer 43

Glycolyisis is upregulalted when the cell needs more ATP, and downregulated when the cell does not need more ATP

Question 44

Describe how negative regulation is used in glycolysis

Answer 44

Certain products inhibit previous steps in glycolysis. I.e, when glucose-6-phospahte (the first product of glycolysis) inhibits hexokinase, which catalyzes the conversion of glucose to glucose-6-phosphate

Question 45

When is gluconeogenesis upregulated?

there are 2 answers

Answer 45

**When the body needs more glucose **AND as an alternate pathway to hadndle surplus pyruvate/acetyl-CoA that builds up

Question 46

True or False

Gluconeogenesis and glycolysis are regulated in tandem to respond to hormonal signaling from outside the body

Answer 46

True

Most notably, the signaling is from insulin and glucagon

Question 47

When does the body break down glycogen?

What is the purpose of glycogen breakdown

Answer 47

When cells need more glucose for gluconeogenesis or glycolysis

Remember: glycogen is how the cells store excess glucose

Question 48

When is glycogen synthesis upregulated?

Answer 48

When the cells have a surplus of glucose

thus needing this glucose to be stored (as glycogen) for later use

Question 49

When there are surplus levels of AMP/ADP, which non-aerobic metabolic pathways are affected and how?

Answer 49

Glycolysis is upregulated because the cell needs energy

AMP rises whenever the ATP:ADP ratio falls, and a high cellular ratio of AMP:ATP is a signal that the energy status of the cell is compromised.

Question 50

When there are high levels of ATP/NADH/citrate, which non-aerobic metabolic pathways are affected and how?

Answer 50

Glycolysis is downregulated because the cell has enough energy

Question 51

When there is excess acetyl-CoA, what non-aerobic metabolic pathway is affected and how?

Answer 51

Gluconeogenesis is upregulated because acetyl-CoA activates pyruvate carboxylase, which converts pyruvate to oxaloacetate (OAA) for use in the gluconeogenic pathway

Inhibition of pyruvate dehydrogenase by acetyl-CoA also increases shunting of pyruvate toward oxaloacetate.

Question 52

How does the presence of glucagon influence the metabolic pathways?

Answer 52

It upregulates gluconeogenesis and downregulates glycolysis

Glucagon acutely stimulates hepatic gluconeogenesis by increasing hepatic acetyl-CoA content and pyruvate carboxylase flux.

Question 53

How does the presence of glucagon affect glycoysis?

Answer 53

Glucagon downregulates glycolysis, whereas insulin upregulates glyclolysis

To increase blood glucose, glucagon promotes hepatic glucose output by increasing glycogenolysis and gluconeogenesis and by decreasing glycogenesis and glycolysis in a concerted fashion via multiple mechanisms.

Question 54

How does insulin affect gluconeogenesis and glycolysis?

Answer 54

Insulin downregulates gluconeogenesis and upregulates insulin

Insulin indirectly stimulates glucose oxidation via increasing glucose uptake and subsequent glycolysis that increases pyruvate supply for mitochondrial glucose oxidation by the pyruvate dehydrogenase (PDH) complex, the rate-limiting enzyme of glucose oxidation. Insulin is the most important hormone that inhibits gluconeogenesis. It acts predominantly by suppressing the expression of the genes for the key gluconeogenic enzymes PEPCK and G-6-Pase.