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1MB Gastroenterology > Biochemistry > Flashcards

Biochemistry Flashcards

(74 cards)

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1
Q

What is glycogenesis?

A

Synthesis of glycogen from glucose

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2
Q

What is glycogenolysis?

A

Breakdown of glycogen to form glucose

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3
Q

Glycogenolysis occurs by hydrolysis. True/False?

A

False

Occurs by phosphorolysis

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4
Q

Where is glycogen stored in the body?

A

Liver

Muscle cells

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5
Q

What is the role of muscle glycogen?

A

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

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6
Q

Which bonds link glucose molecules to form glycogen?

A

Alpha-1,4-glycosidic bonds

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7
Q

Which bonds create branches in the glycogen chain?

A

Alpha-1,6-glycosidic bonds

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8
Q

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

A

False

Glucose residues can only be added to an existing glycogen chain

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9
Q

What is required to begin glycogen formation?

A

Glycogenin

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10
Q

What is Glycogenin?

A

A glycogen primer containing 4 glucose monomers

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11
Q

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

A

Glycogen synthase

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12
Q

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

A

Glucose-1-phosphate

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13
Q

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

A

UDP-glucose

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14
Q

What is UDP-glucose?

A

Essentially an active form of glucose

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15
Q

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

A

True

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16
Q

How often are branches introduced into the glycogen chain?

A

Every 10 glucose molecules

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17
Q

When does glycogenolysis occur?

A

Between meals to maintain blood glucose levels

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18
Q

Which enzyme catalyses glycogenolysis?

A

Glycogen phosphorylase

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19
Q

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

A

True

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20
Q

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

A

Stimulates glycogen synthesis

Inhibits glycogen phosphorylase

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21
Q

What are the 2 regulatory actions of glucagon upon glycogenolysis?

A

Stimulates glycogen breakdown

Inhibits glycogen synthase

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22
Q

What is gluconeogenesis? When does it occur?

A

Synthesis of glucose from non-carbohydrate precursors

Occurs when glycogen stores are completely depleted

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23
Q

Where does gluconeogenesis mainly occur?

A

Liver

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24
Q

Name the 3 main precursors for gluconeogenesis

A

Lactate (lactic acid)
Amino acids
Glycerol

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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

1MB Gastroenterology (23 decks)

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