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Biochemistry I > Chapter 8: Enzyme Control Mechanisms > Flashcards

Chapter 8: Enzyme Control Mechanisms Flashcards

1
Q

Enzyme time frames

A
  • Short (allosteric control)
  • Medium (covalent modification)
  • Long (induction and repression)
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2
Q

Enzyme control mechanisms

A
  • Feedback and feedforward inhibition
  • Phosphorylation/dephosphorylation
  • Calcium binding proteins
  • Proteolytic activation
  • Allosteric control
  • Induction/repression
  • Substrate availability
  • Compartmentalization
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3
Q

Characteristics of biochemical reactions in pathways

A
  • Highly ordered enzyme sequence
  • Tightly controlled
  • Often by factors other than substrate
  • Environmental changes influence flux
  • Non equilibrium enzymes are key
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4
Q

Long time frame activity

A
  • Gene expression
  • Alters the amount of enzyme made
  • Days or weeks
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5
Q

Action of cortisol

A
  • Slow to turn on enzymes
  • Makes more enzymes
  • We don’t want epi and norepi on all the time
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6
Q

Medium time frame activity

A
  • Covalent modification

- Reversible phosphorylation/adenylation

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7
Q

Phosphate group is negative and will impact/change enzyme activity

A
  • Doesn’t always increase activity, always changes though
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8
Q

Short time frame activity

A
  • Allosteric effectors

- Noncovalent interactions

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9
Q

Long time scale changes

A
  • Induction and repression
  • Changes in the AMOUNT of enzyme synthesized
  • Lac operon is good example (large dynamic range)
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10
Q

Enzyme activity if lactose is present

A
  • Bact make the enzymes to break down the lactose

- If it is not present we turn the gene off

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11
Q

Medium time scale changes

A
  • Covalent modification of enzyme structure
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12
Q

Reversible phosphorylation (medium) occurs at

A
  • Serine and threonine residues

- Enzymes cycle between active and inactive forms

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13
Q

Changes in medium time frame scale mediated by

A
  • Hormone-receptor cell interactions at the cell surface
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14
Q

Covalent modification of amino acid residues on enzymes coordinates

A
  • Control of muscle glycogen metabolism
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15
Q

Phosphorylation in medium time frame reactions activates/inhibits

A
  • Activates glycogen phosphorylase

- Inhibits glycogen synthase

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16
Q

Allosteric activators/inhibitors in short time frames bind to

A
  • Bind reversibly (noncovalently) to the allosteric site on allosteric enzymes
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17
Q

GMP and AMP feedback inhibition regulates and inhibits

A
  • Regulates purine biosynthesis

- Inhibits glutamine PRPP amidotransferase

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18
Q

Control mechanism of the irreversible steps of glycolysis

A
  • Feedback inhibition and feedforward inhibition
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19
Q

Phosphorylation/dephosphorylation (type of modification)

A
  • Reversible covalent modification
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20
Q

Residues that can be phosphorylated

A
  • Serine
  • Threonine
  • Tyrosine
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21
Q

Glycogen phosphorylase activity enhanced by

A
  • Covalent reversible phosphorylation
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22
Q

Glycogen phosphorylase kinase is controlled by

A
  • Reversible phosphorylation
23
Q

Examples of reversible phosphorylation/dephosphorylation

A
  • Glycogen phosphorylase
  • Adenylation
  • Methylation
24
Q

Calmodulin (calcium binding protein) found in

A
  • Ubiquitous
  • Found in the cytoplasm
  • Component of several enzymes
25
Q

Calcium binding to calmodulin activates

A
  • Calcium-calmodulin dependent kinases
26
Q

Importance of calcium binding proteins

A
  • Signal transduction mechanisms for hormones:
  • Vasopressin
  • Oxytocin
  • Angiotensin II
27
Q

Limited proteolysis modification

A
  • Permanent modification of inactive proenzymes (zymogenic precursors)
  • Not reversible
  • Can be extracellular
  • Digestive enzymes and coagulation cascade
28
Q

Digestive enzymes and coagulation cascade enzymes

A
  • Pepsinogen

- Trypsinogen

29
Q

Limited proteolysis is not a control mechanism

A
  • It is an activation mechanism
30
Q

Limited proteolysis activates

A
  • Digestive enzymes

- Clotting factors

31
Q

Induction/repression regulated by

A
  • Controlling enzyme synthesis
32
Q

Induction ( + ) or repression ( - ) of gene transcription works at level of

A
  • Mechanism working at level of gene expression
33
Q

Selective proteolytic degradation

A
  • Done by proteosomes with ubiquitin system

- Reduces enzyme levels

34
Q

Slow mechanisms for regulating enzyme concentration (induction/repression)

A
  • Changes occur over hours, days, or even weeks

- Long time frame

35
Q

Main site of control for eukaryotic gene expression

A
  • First step

- Transcription of DNA sequence into RNA

36
Q

Cortisol

A
  • Steroid hormone than can induce gluconeogenic enzymes
37
Q

Steroid hormones

A
  • Interact with nuclear or cytoplasmic receptors

- Alter enzyme synthesis

38
Q

Cortisol mechanism

A
  • Diffuses through membrane
  • Binds to intracellular receptors or in nucleus
  • Turns on gene expression
39
Q

Cortisol increases synthesis of

A
  • Transcription and translation (making new proteins)
40
Q

Compartmentalization is aided by

A
  • Subcellular specialization

- Selectively permeable membranes

41
Q

Fatty acid oxidation occurs in

A
  • The mitochondria
42
Q

Fatty acid synthesis occurs in

A
  • The cytosol
43
Q

Glycolysis occurs in

A
  • The cytosol
44
Q

Citric acid cycle occurs in

A
  • The mitochondria
45
Q

Availability of substrates is critical

A
  • Crucial in compartmental control
46
Q

Endoplasmic reticulum

A
  • Delivery of proteins

- Synthesis of lipids for membranes

47
Q

Nucleus

A
  • Nucleic acid synthesis
48
Q

Mitochondria

A
  • Citric acid cycle
  • Oxidative phosphorylation
  • Fatty acid breakdown
49
Q

Cytosol

A
  • Fatty acid synthesis
  • Glycolysis
  • Gluconeogenesis
  • Pentose phosphate pathway
50
Q

Golgi apparatus

A
  • Sorting and secretion of proteins
51
Q

Control

A
  • The ability to alter metabolic flux in a pathway as needed
52
Q

Irreversible and non-equilibrium enzymes

A
  • Achieves metabolic control
53
Q

Purpose for control of enzyme activity

A
  • Avoids unnecessary metabolic activity/utilization of resources
  • Prevents accumulation of excess product
54
Q

Most common control mechanisms

A
  • Altering concentration
  • Covalent/allosteric modification
  • Proteolysis
  • Compartmentalization

Biochemistry I (34 decks)

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