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Flashcards in Biochemistry Deck (74):
1

What is glycogenesis?

Synthesis of glycogen from glucose

2

What is glycogenolysis?

Breakdown of glycogen to form glucose

3

Glycogenolysis occurs by hydrolysis. True/False?

False
Occurs by phosphorolysis

4

Where is glycogen stored in the body?

Liver
Muscle cells

5

What is the role of muscle glycogen?

Not used to maintain blood glucose; provides energy via glycolysis and TCA cycle during physical activity

6

Which bonds link glucose molecules to form glycogen?

Alpha-1,4-glycosidic bonds

7

Which bonds create branches in the glycogen chain?

Alpha-1,6-glycosidic bonds

8

Glycogen formation can be started by two glucose monomers joining together. True/False?

False
Glucose residues can only be added to an existing glycogen chain

9

What is required to begin glycogen formation?

Glycogenin

10

What is Glycogenin?

A glycogen primer containing 4 glucose monomers

11

Which enzyme effectively adds glucose monomers to Glycogenin to produce glycogen?

Glycogen synthase

12

When enough glucose is present, glycogen synthesis begins: glucose-6-phosphate is converted to what?

Glucose-1-phosphate

13

What is formed from glucose-1-phosphate in glycogen synthesis?

UDP-glucose

14

What is UDP-glucose?

Essentially an active form of glucose

15

Glycogen synthase adds only one glucose at a time to UDP-glucose to ultimately form glycogen. True/False?

True

16

How often are branches introduced into the glycogen chain?

Every 10 glucose molecules

17

When does glycogenolysis occur?

Between meals to maintain blood glucose levels

18

Which enzyme catalyses glycogenolysis?

Glycogen phosphorylase

19

Glycogen phosphorylase cleaves off only one glucose at a time from glycogen. True/False?

True

20

What are the 2 regulatory actions of insulin upon glycogen synthesis?

Stimulates glycogen synthesis
Inhibits glycogen phosphorylase

21

What are the 2 regulatory actions of glucagon upon glycogenolysis?

Stimulates glycogen breakdown
Inhibits glycogen synthase

22

What is gluconeogenesis? When does it occur?

Synthesis of glucose from non-carbohydrate precursors
Occurs when glycogen stores are completely depleted

23

Where does gluconeogenesis mainly occur?

Liver

24

Name the 3 main precursors for gluconeogenesis

Lactate (lactic acid)
Amino acids
Glycerol

25

Which TCA cycle intermediate is needed for gluconeogenesis? Why is it needed?

Oxaloacetate (4C)
Accepts acetyl groups from fat breakdown

26

Describe the Cori Cycle

Blood transports lactate to liver
Liver converts lactate to glucose
Glucose is released into blood

27

Which type of amino acids can be used to synthesise new glucose?

Glucogenic amino acids

28

Which type of amino acids cannot be used to synthesise new glucose?

Ketogenic amino acids

29

What effect do insulin and glucagon have on gluconeogenesis?

Insulin inhibits gluconeogenesis
Glucagon stimulates gluconeogenesis

30

Does ATP stimulate gluconeogenesis?

Yes

31

What happens when increased fat intake is not coupled with appropriate energy expenditure?

OBESITY
Increase in number and size of adipocytes

32

Fat provides us with 2x more energy than carbohydrates. True/False?

True

33

What are essential fatty acids?

Fatty acids required by, but cannot be synthesised by, the body

34

Name some fat-soluble vitamins

Vitamin A, D, E, K

35

What do triglycerides consist of?

Glycerol attached via ester bond to 3 fatty acids

36

Double bonds in fatty acids are usually in the trans configuration. True/False?

False
Usually in cis configuration

37

What effect do double bonds have on the melting point of fatty acids?

The greater the no. of double bonds, the lower the melting point

38

What are the main products of lipid digestion?

Glycerol
Fatty acids
Monoglycerides

39

What must happen to long-chain fatty acids to make them transportable?

Resynthesised to triglyceride and coated into a chylomicron, which enters the lymph

40

What happens to chylomicrons at muscle and adipose tissue?

Cleaved by lipoprotein lipase into free fatty acids

41

What happens to free fatty acids at muscle and adipose tissue?

Resynthesised into triglyceride or oxidised to provide energy

42

Where does further oxidation of fatty acid occur?
Why is this a problem for acyl-CoA?

Oxidation occurs in the mitochondrial matrix
acyl-CoA is formed in the cytoplasm!

43

What transports acyl-CoA into the mitochondrial matrix?

Carnitine shuttle

44

How is acyl-carnitine formed in the cytoplasm?

Fatty acids are transferred from acyl-CoA to carnitine to form acyl-carnitine

45

How does acyl-carnitine get across the inner membrane into the matrix? What happens to the carnitine?

Via a transporter
Carnitine is cleaved off, leaving acyl group

46

In the matrix, what happens to the free acyl- group?

Combines with CoA again to form acyl-CoA
Net effect: acyl-CoA ends up in the matrix!

47

What happens to acyl-CoA in the matrix?

Shortened by 2C to form acetyl-CoA and a new acyl-CoA

48

What are the products of one round of B-oxidation of fatty acid?

1 acetyl-CoA
1 acyl-CoA, shortened by 2C
1 FADH2
1 NADH + H

49

How and where are ketone bodies formed?

Formed from acetyl-CoA during B-oxidation in liver mitochondria

50

What is lipogenesis?

Synthesis of fatty acids

51

Lipogenesis is a reductive process (electrons are required). True/False?

True

52

What transports acetyl-CoA from mitochondrial matrix into cytoplasm?

Citrate

53

What is the vital first step in lipogenesis from acetyl-CoA?

Activation of acetyl-CoA by acetyl-CoA carboxylase into malonyl-CoA

54

Which enzyme catalyses synthesis of long chain fatty acid from malonyl-CoA, acetyl-CoA and NADH?

Fatty acid synthase

55

Which component of fatty acid synthase carries the growing fatty acid chain during synthesis?

Acyl-carrier protein (ACP)

56

When a fatty acid chain length of __C is reached, the fatty acid is released

16C

57

Synthesis of fatty acids is maximal when carbohydrate is scarce. True/False?

False
Synthesis occurs when carbohydrate is in plentiful supply + fatty acids are scarce (otherwise lipolysis would occur)

58

Amino acids which are not used for proteins are stored in the liver. True/False?

False
Amino acids cannot be stored and are degraded if not used as building blocks

59

Where is the major site of amino acid degradation?

Liver

60

What does amino acid degradation primarily produce?

Ammonia (NH3) and ammonium ions

61

What are the 3 steps by which urea is formed?

Transaminiation
De-amination
Urea cycle

62

Which organ is albumin secreted from?

Liver

63

Name the main liver-derived plasma proteins (4), in order of increasing molecular weight

Albumin
alpha-globulins
beta-globulins
gamma-globulins

64

What characteristic of plasma proteins enables them to maintain osmotic pressure which increases fluid movement out of the tissues into the blood?

They are insoluble - they do not diffuse into the interstitial fluid and only circulate in the blood

65

List some hydrophobic substances that are carried in the blood by plasma proteins (4)

Steroid hormones
Free fatty acids
Bilirubin
Cholesterol

66

Give 2 examples of alpha-globulin plasma proteins

Ceruloplasmin
Retinol-binding protein

67

Give 2 examples of beta-globulin plasma proteins

Transferrin
Fibrinogen

68

Transferrin transports Fe2+ (ferrous iron). True/False?

False
Transports Fe3+ (ferric iron)

69

What is the most abundant plasma protein in the blood?

Albumin

70

Insulin inhibits production of albumin. True/False?

False
Insulin stimulates production of albumin

71

Are albumin levels low or high in liver disease?

Low

72

Iron is transported in the ferrous/ferric state bound to ____, and is stored in the ferrous/ferric state bound to ____

Iron is transported in the ferric state bound to transferrin, and is stored in the ferrous state bound to ferritin

73

Which plasma protein does copper bind to for transport?

Ceruloplasmin

74

Which disease results due to accumulation of copper due to deficiency of ceruloplasmin?

Wilson's disease