Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biochemistry > Chapter 18 > Flashcards

Chapter 18 Flashcards

1
Q

What are the four amino acids that play key roles in the transport and distribution of amino acids

A

alanine, glutamate, glutamine, aspartate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Once proteins are broken down into amino acids what are their two potential fates

A
  • recycled into new proteins
  • oxidized for energy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

______ is a hormone secreted within gastric mucosa when protein enters the stomach

A

Gastrin, stimulates HCl and pepsinogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Under low pH what happens to pepsinogen ?

A

at low ph pepsinogen gets autocatalytically cleaved into pepson

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What does pepsin do?

A

cuts proteins into peptides in the stomach

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What hormone is secreted in the small intestine in response to low pH

A

secretin, it stimulates pancreas exocrine cells to secrete bicarbonate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What hormone is secreted in response to peptides entering the duodenum ?

A

cholecystokinin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

The autocatalytic hydrolysis of pepsinogen is signaled by what

A

hormone gastrin and low pH

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Pepsin cleaves after what amino acids

A

Leu, Phe, Trp, Tyr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Trypsin cleaves after what amino acids

A

the positively charged amino acids, Lys & Arg

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Chymotrypsin cleaves after what amino acids

A

aromatic amino acids Phe, Trp, Tyr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How is chymotrypsin activated

A

by the hydrolysis of trypsin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What cleaves successive carboxyl-terminal residues

A

carboxypeptidase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What cleaves successive amino terminal residues

A

Aminopeptidases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Role of pancreatic trypsin inhibitor

A

protein inhibitor that protects the pancreas against self-destruction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Where are free amino acids absorbed

A

in the villi off the intestinal mucosa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

where does oxidative deamination occur

A

within the mitochondrial matrix

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Humans and great apes excrete both urea (from amino acids) and _______ (from purines)

A

we excrete urea and uric acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Glutamate and glutamine can both be converted into _____ for use in the citric acid cycle

A

glutamate —-> alpha ketoglutarate
glutamine —–> alpha ketoglutarate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

alanine can be converted into _____ for use in the citric acid cycle

A

alanine —> pyruvate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

aspartate can be converted into ______ for use in the CAC

A

aspartate —-> oxaloacetate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Transaminations are catalyzed by _____?

A

aminotransferases which use the cofactor pyridoxal phosphate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

oxidative deamination is catalyzed by what enzyme?

A

L-glutamate dehydrogenase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is oxidative deamination positively regulated by?

A

ADP, low levels of glucose

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is oxidative deamination negatively regulated by?

A

GTP, high levels of alpha ketoglutarate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

ammonia is processed into _____ for excretion

A

urea so it can be excreted through the urea cycle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Alpha-ketoglutarate can enter the citric acid cycle or be used for _______

A

gluconeogenesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What molecule serves as an ammonia transporter

A

Glutamine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What does alanine aminotransferase create in the muscle and what in the liver

A

in muscle: creates alanine
in liver: creates glutamate and pyruvate

30
Q

What makes free ammonia so toxic to the brain

A

Ammonia (NH4+) competes with K+ for transport into astrocytes via Na+K+ATPase , causing an elevated level of extracellular K+

31
Q

The pathway by which ammonia brought to the mitochondria of hepatocytes (epithelial liver cells) is converted to urea

A

Urea cycle

32
Q

1st nitrogen acquiring reaction of the urea cycle?

A

carbamoyl phosphate synthesis
- catalyzed by carbamoyl phosphate synthetase 1

33
Q

What pathways link urea and citric acid cycles?

A

aspartate-argininosuccinate shunt

34
Q

What shuttle converts aspartate to malate via oxaloacetate

A

the malate-aspartate shuttle

35
Q

The presence of peptides in the duodenum causes the release of the blood hormone ______ which stimulates the secretion of several pancreatic proteases

A

cholecystokinin

36
Q

Alpha-ketoglutarate can enter the citric acid cycle or be used for _______

A

gluconeogenesis

37
Q

what enzyme catalyzes the conversion of inactive trypsinogen to active trypsin

A

enteropeptidase (a proteolytic enzyme secreted by intestinal cells)

38
Q

Why are digestive enzymes synthesized as inactive precursors

A

to protect exocrine cells from destructive proteolytic attack

39
Q

What does bicarbonate do in the small intestine

A

neutralizes gastric HCl, returning the pH to 7

40
Q

All transaminases have ______ as a cofactor

A

PLP (pyridoxal phosphate)

41
Q

In the mitochondria, glutamate undergoes oxidative deamination catalyzed by _______ to produce ________ and ________

A

catalyzed by L-glutamate dehydrogenase to produce alpha-ketoglutarate and NH4+

42
Q

Free ammonia is combined with glutamate to yield _______ via glutamine synthetase

A

glutamine

43
Q

Excess glutamine goes to the intestine, liver & kidneys where it is converted into _______ and _______ by glutaminase

A

glutamine —> glutamate + NH4+

44
Q

______ can replace glutamine in the transport of amino groups from muscle —> liver in a non-toxic form

A

Alanine

45
Q

Pyruvate and alanine are interconverted via transamination with glutamate via the enzyme __________

A

alanine transaminase

46
Q

What is the goal of the urea cycle?

A

to eliminate ammonia from the body by converting it into urea

47
Q

When is the expression of urea cycle enzymes increased ?

A
  • high protein diet
  • starvation, when protein is being broken down for energy
48
Q

Ketogenic Amino Acids

A

amino acids that can be converted into ketone bodies through ketogenesis

  • converted into Acetyl-CoA
49
Q

Glucogenic Amino Acids

A

amino acids that can be converted into glucose through gluconeogenesis (and therefore pyruvate)
- all of the amino acids except Lysine, Leucine

50
Q

What amino acids are exclusively ketogenic

A

Leucine & Lysine

51
Q

What amino acids are both ketogenic and glucogenic

A

Phe, Try, Tyr, Isoleucine, Lysine

52
Q

Carbamoyl phosphate is synthesized by carbamoyl phosphate synthetase 1 from ______ & ______

A

Carbamoyl phosphate is synthesized from NH4+ and HCO3- (requires 2 ATP)

53
Q

What is the second nitrogen-acquiring reaction in the urea cycle ?

A

aspartate entry into urea cycle, performed by arginosuccinate synthetase

54
Q

How is the energetic cost of the urea cycle reduced?

A

by cycle interconnections (ex: fumarate to malate, leading to NADH generation in the mitochondria)

55
Q

What are the cofactors for the catabolism of amino acids that involve one-carbon transfers

A
  • biotin
  • tetrahydrofolate (THF)
  • S-adenosylmethionine
  • Pyridoxal phosphate (PLP)
56
Q

What is the preferred cofactor for methyl transfer in biological reactions?

A

S-Adenosylmethionine

57
Q

What enzyme catalyzes the conversion of serine to pyruvate

A

serine dehydratase, PLP dependent

58
Q

Cholecystokinin stimulates the release of what pancreatic proteases

A

Trypsinogen
Chymotrypsin
Procarboxypeptidases A&B (the zymogens of carboxypeptidases A&B)

59
Q

This cofactor functions as an intermediate carrier of amino groups at the active site of transaminases

A

PLP, the coenzyme form of pyridoxine (B6)

60
Q

What activates carbamoyl phosphate synthase I

A

N-acetylglutamate which is formed by N-acetylglutamate when glutamate and acetyl CoA concentrations are high
- activated by Arginine

61
Q

What two amino acids can produce oxaloacetate

A

Asparagine and Aspartate

62
Q

Where are the branched amino acids (Leucine, Isoleucine, Valine) degraded?

A

NOT in the liver
- degraded in the extrahepatic tissues of the muscle, adipose, kidney, brain

63
Q

What enzymes catalyze the breakdown of branched-chain amino acids into acetyl-CoA derivatives

A
  • branched chain aminotransferase
  • branched chain alpha keto acid dehydrogenase complex
64
Q

Under what 3 circumstances do amino acids undergo oxidative degradation?

A
  1. Amino acids released during normal protein turnover are not needed for new protein synthesis.
  2. Dietary amino acids exceed the body’s needs for protein synthesis.
  3. Cellular proteins are used as fuel because carbohydrates are either unavailable or not properly utilized due to starvation or uncontrolled diabetes mellitus.
65
Q

In transaminations, what accepts the amino group

A

alpha-ketoglutarate

66
Q

The first step in the catabolism of most l-amino acids, once they have reached the liver, is ?

A

The removal of the alpha amino groups by aminotransferases

67
Q

PLP is covalently bound to an enzymes active site through a _______ linkage

A

ALDIMINE (Schiff base) linkage to the amino group of Lysine

68
Q

The first step in most PLP-catalyzed reactions is aldimine displacement. Explain

A

Aldimine Displacement
- the aldimine linkage to Lys is replaced by the amino group of an amino acid

69
Q

What is the role of PLP in reactions at the alpha carbon such as transaminations, decarboxylation, racemizations

A

PLP provides resonance stabilization to the carbanion intermediates

  • its highly conjugated structure allows for delocalization of the negative charge
70
Q

Oxidative Deamination can use _____ or _____ as an electron acceptor

A

NAD+ or NADP+

71
Q

What is the second major source of ammonia in hepatocyte mitochondria

A

Glutamine

72
Q

What are the two nitrogen-acquiring reactions of the urea cycle?

A
  1. Carbamoyl phosphate synthesis
  2. Aspartate entry into the urea cycle by arginosuccinate synthetase

Biochemistry (10 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions