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Science for Medicine > Life at the cellular level, Enzymes, Forces acting across membranes > Flashcards

Life at the cellular level, Enzymes, Forces acting across membranes Flashcards

1
Q

What are the two laws of thermodynamics?

A
  1. Energy can be CONVERTED from one form to another but the total energy of the universe remains constant.
  2. All energy transformations lead to more disorder.
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2
Q

How do cells maintain order?

A

By performing anabolic and catabolic reactions.

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3
Q

What is delta G (free energy) equal to?

A

deltaG = deltaH - TdeltaS

H = heat released
T = absolute temp
S = entropy
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4
Q

What does a negative deltaG value indicate?

A

Gives off free energy, catabolic, spontaneous, increase entropy

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5
Q

What does a positive deltaG value indicate?

A

Takes in free energy, anabolic, energetically unfavourable

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6
Q

What reaction is energetically favourable?

A

Catabolic reaction (negative delta G)

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7
Q

What reaction is energetically unfavourable?

A

Anabolic (positive delta G)

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8
Q

What type of reaction increases entropy?

A

Catabolic

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9
Q

What type of reaction is spontaneous?

A

Catabolic

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10
Q

What are catabolic and anabolic reactions coupled?

A

Maintain a dynamic steady state of free energy flow.

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11
Q

What type of reaction is exergonic and give an example?

A

Catabolic e.g hydrolysis

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12
Q

What type of reaction is endergonic and give an example?

A

Anabolic e.g condensation

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13
Q

Describe metabolism.

A

Chemical process, food used for tissue growth, catalysed by enzymes, intermediate metabolites, spontaneous reactions.

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14
Q

What is the function of NAD+/NADP+ and FAD?

A

Act as co-enzymes/ electron carrier molecules. FAD captures two H+ ions whereas, NAD+/NADP+ has one reactive site.

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15
Q

What is the function of ATP?

A

“Universal currency”, stores energy and uses phosphoric group transfer between molecules for energy flow.It breaks down to ADP + Pi to supply free energy.

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16
Q

Where does substrate level phosphorylation occur?

A

In cytosol and mitochondria.

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17
Q

Where does oxidative phosphorylation occur?

A

Inner membrane of mitochondria.

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18
Q

What is substrate-level phosphorylation?

A

Phosphorylates ADP from substrate to ATP using kinases.

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19
Q

Give an example of substrate-level phosphorylation.

A

Glycolysis

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20
Q

What is oxidative phosphorylation?

A

Nutrients or chemicals provide energy to transfer a phosphate group to ADP and produce ATP with the help of the electron transport chain, NADH electron carriers and ATP synthase, O2.

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21
Q

what are the four major elements that construct human biomolecules?

A

C, H, O, N

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22
Q

Explain why polarity of C-C bonds are crucial.

A
  1. C-C and C-H share electrons so stable.
  2. C-O, C-N, C-functional group highly polar so alter C-bond reactivity.
  3. C-C rotates freely
  4. C=C don’t rotate (rigid)
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23
Q

What are the 5 kinds of chemical reactions?

A
  1. Redox (OILRIG)
  2. Making/Breaking C bonds
  3. Internal re-arrangements
  4. Group transfers
  5. Condensation and Hydrolysis
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24
Q

Give an example of a redox reaction.

A

Glucose to 2 x pyruvate (glycolysis)

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25
Q

Give an example of making/breaking bonds.

A

Cleavage of glucose in glycolysis.

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26
Q

Give an example of internal re-arrangements.

A

Glycolysis (before glucose is split)

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27
Q

Give an example of group transfers.

A

Glycolysis (phosphate group transfer for ATP production)

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28
Q

Give examples of condensation and hydrolysis reactions.

A

All sub-units of proteins, polysaccharides and nucleic acids are Broken by Hydrolysis and Joined by Condensation.

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29
Q

Describe the structure of polysaccharides.

A

Polymers of sugar molecules linked by glycosidic bonds.

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30
Q

Describe the structure of proteins.

A

Polymers of AA monomers linked by peptide bonds.

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31
Q

Describe the structure of nucleic acids.

A

Polymers of nucleotide monomers linked by 3’, 5’-phosphodiester bonds.

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32
Q

Describe the structure of lipids.

A

One or more long chain fatty acids with a carboxyl group and hydrocarbon fatty acid chain.

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33
Q

What structures are absent form prokaryotic cells compared to eukaryotic cells.

A
  1. Nuclear membrane
  2. Mitochondria
  3. Membrane bound structures
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34
Q

What is the role of the nucleus?

A

Contains histone proteins, DNA, nucleoprotein and some RNA, enclosed by phospholipid bilayer.

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35
Q

What is the role of the rough ER and Golgi?

A

Central dogma i.e transcription and translation and role in protein modifications and transport.

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36
Q

What is the role of the lysosome?

A

Separate enzymes from rest of cell, used in autophagy or digestion of engulfed particles.

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37
Q

What is the role of mitochondria?

A

Matrix contains binding sites for calcium and enzymes for oxidation. Has it’s own ribosomes and circular DNA so will self-replicate.

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38
Q

What are cilia and flagella?

A

Cell surface projections made of microtubules.

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39
Q

What is the role of the peroxisome?

A

Breakdown long chain FAs through beta-oxidation.

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40
Q

Describe the structure of the cell membrane.

A
  1. Proteins embedded
  2. Phospholipid bilayer (amphipathic)
  3. Attached to cytoskeleton and ECM for cell-cell recognition
41
Q

What is the role of the cytoskeleton?

A

Supports and maintains cell shape, holds organelles in position, moves organelles involved in cytoplasmic streaming.

42
Q

What junctions can be found on the eukaryotic plasma membrane?

A
  1. Anchoring
  2. Gap
  3. Channel forming
  4. Adhesive (adherens - actin or desmosomes - keratin)
  5. Tight
43
Q

Name 5 functions of the cell membrane.

A
  1. Signal transduction (by receptors)
  2. Enzyme activity
  3. Transport
  4. Intracellular joining
  5. Cell-cell recognition
  6. Signalling (synaptic, endocrine, paracrine)
44
Q

What is the cytoskeleton composed of?

A
  1. Microfilaments (actin)
  2. Intermediate filaments (fibrous proteins) and
  3. Microtubules (tubular- alpha and beta sub-units).
45
Q

Define hydrogen bond.

A

Weak bond between two molecules resulting from an electrostatic attraction between a proton in one molecule (electropositive) and an electronegative atom in another (usually O or N).

46
Q

Are molecules that form H-bonds water soluble?

47
Q

What type of H bonds are angled?

A

Weak H bonds.

48
Q

Describe the interactions between water molecules and solutes that determine solubility.

A

Molecules that form H bonds are water soluble.
When dissolved, water-water H bonds and solute-solute H bonds are replaced with more energetically favourable solute-water H bonding.

49
Q

Describe amphipathic and give an example.

A

Contains hydrophobic and hydrophilic parts e.g phospholipids and proteins.

50
Q

Define pH.

A

Expresses acidity or alkalinity on a log scale. pH = -log10C (c=H+ ions in moles/litre).

51
Q

What equation relates the degree of proton dissociation of a weak acid to it’s ionisation constant and the pH?

A

Henderson-Hasslebach Equation

52
Q

What is the Henderson-Hassleback equation?

A

pH = pKa + log ([A-]/[HA])

53
Q

What type of solution donates protons?

54
Q

What type of solution accepts protons?

55
Q

What types of solutions fully dissociate?

A

Strong acids and strong bases (weak only partially dissociate)

56
Q

Define buffer.

A

Weak acid which maintains optimal pH for optimal activity.

57
Q

Give two examples of buffer systems in the human body.

A
  1. Phosphate system (in cells)

2. Bicarbonate system (in plasma)

58
Q

What equation can be used to check how much buffering capacity remains in patients with metabolic acidosis?

A

Henderson-Hassleback equation

59
Q

Discuss the three main ways enzymes catalyse reactions.

A
  1. Increase rate of spontaneous reaction
  2. Decrease activation energy
  3. Accelerate movement towards reaction equilibrium
60
Q

What do enzymes NOT do?

A
  1. Move reaction equilibria

2. Make a non-spontaneous reaction spontaneous.

61
Q

What happens if substrate concentration is increased?

A

Increase initial rate of reaction.

62
Q

Define ‘Michaelis Constant’.

A

Km. Measurement of affinity of an enzyme with substrate. It is approximately equivalent to the substrate concentration at which the initial reaction rate is half of the Vmax.

63
Q

What does a larger Km suggest?

A

Less stable ES complex (less affinity enzyme has for substrate).

64
Q

What does a smaller Km suggest?

A

More stable ES complex (more affinity enzyme has for substrate).

65
Q

What is the Lineweaver-Burk plot used for?

A

To define Vmax and Km.

66
Q

What does Km equal?

A

Rate at which ES is broken down/ rate at which ES is formed.

67
Q

What equation is used to describe the hyperbolic curves?

A

Michaelis-Menten equation.

68
Q

How can you predict the speed of the reaction (Vo)?

A

Vo = (Vmax+[S]/Km +[S])

69
Q

Describe competitive enzymes.

A

Bind non-covalently and resemble substrate so competes for active site.

70
Q

Describe non-competitive enzymes.

A

Bind non-covalently to another site (not the active site).

71
Q

Compare Vmax and Km in competitive and non-competitive enzymes.

A
  1. Competitive = high Km and unchanged Vmax

2. Non-competitive = unchanged Km and low Vmax

72
Q

Describe allosterically-regulated enzymes.

A

Activate or inhibit.
Cell metabolites binding non-covalently to a non-active site changes enzyme structure in 2 ways:
1. Concerted (subunits exist in 2 conformations and flip between 2 when no substrate is bound)
2. Sequential (no flipping, binding causes conformational change.

73
Q

Describe covalently modified enzymes.

A
  • Reversible
  • Regulate enzymes e.g protein kinases and protein phosphates and other proteins
  • Example = Phosphorylation.
74
Q

What lab test can be used to identify enzymes?

A

Electrophoresis.

75
Q

Define isozymes.

A

Products of different genes but similar function.

76
Q

Discuss use of enzyme assays in clinical diagnosis.

A

Any disease or trauma cause massive release of enzymes (usually contained in cells) into blood. Example: creatinine kinase increase in blood diagnostic of MI.

77
Q

Describe the basic structure of the membrane.

A
  • Thin bilayer of phospolipids (hydrophobic tails inside and hydrophilic head outside)
  • Embedded with proteins (receptors, transporters, enzymes, associated peripheral membrane associated.
  • Glycoprotein
  • Glycolipid
78
Q

What are the functions of membrane proteins?

A
  1. Selective barrier
  2. Permeability (can vary)
  3. Receptors
  4. Transporters
  5. Peripheral (don’t span core) - maintain structure, attach cells to ECM and perform signalling functions.
79
Q

Define diffusion.

A

Molecules spread from high to low concentrations until desired equilibrium reached.

80
Q

Where can diffusion occur?

A
  1. Through lipid bilayer

2. Through channels e.g aquaporins (molecules like glucose too large to pass through)

81
Q

What are the two types of channels found on the cell membrane?

A
  1. Voltage-gated (changes in membrane potential)

2. Ligand-gated (bind to chemical)

82
Q

What is facilitated diffusion?

A

Use carrier mediated proteins and ATP to move AGAINST concentration gradient e.g Na+/K+ pump (3Na+ out and 2K+ in)

83
Q

What factors favour diffusion through the lipid bilayer?

A

Small, uncharged, lipophilic (hydrophobic)

84
Q

Define electrochemical gradient.

A

The ions creating the concentration gradient are charged particles therefore, an electrical gradient is created.

85
Q

Explain carrier mediated transport systems.

A

Movement of molecules down an electrochemical gradient through transport proteins (facilitated diffusion).

86
Q

Define osmolarity.

A

Number of osmoles of solute/litre (osmoles/L)

87
Q

Define osmolality.

A

Number of osmoles of solute/kg of solvent (osmoles/kg).

88
Q

What determines osmolarity?

A

Penetrating AND non-penetrating particles.

89
Q

Define isosmotic.

A

Same total number of solute particles as ECF.

90
Q

Define hypo-osmotic.

A

Fewer solute particles (must also be hypotonic).

91
Q

Define hyper-osmotic.

A

Greater number of solute particles.

92
Q

What determines tonicity?

A

Non-penetrating particles.

93
Q

Describe the difference between isosmotic and isotonic.

A 
Isosmotic = same number of solute particles as ECF.
isotonic = same number of non-penetrating solute particles as ECF.
94
Q

Describe exocytosis.

A

Active transport of molecules out of cell using energy.

95
Q

Name three types of endocytosis.

A

Phagocytosis, pinocytosis and receptor mediated (all forms of active transport in which cell transports molecules into cell).

96
Q

Energetically unfavourable reactions can only proceed because?

A

They are couple to catabolic reactions.

97
Q

The lipid membrane surrounding eukaryotic cells does not contain?

A

Ribosomes.

98
Q

The lipid membrane surrounding eukaryotic cells does contain?

A

Carbohydrates, cholesterol, ion channels and receptors.

99
Q

The dissociation constant of water is equal to?

A

1x10^14 (mol/L)^2

Science for Medicine (8 decks)

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