Life at the cellular level, Enzymes, Forces acting across membranes Flashcards
1
Q
What are the two laws of thermodynamics?
A
- Energy can be CONVERTED from one form to another but the total energy of the universe remains constant.
- All energy transformations lead to more disorder.
2
Q
How do cells maintain order?
A
By performing anabolic and catabolic reactions.
3
Q
What is delta G (free energy) equal to?
A
deltaG = deltaH - TdeltaS
H = heat released T = absolute temp S = entropy
4
Q
What does a negative deltaG value indicate?
A
Gives off free energy, catabolic, spontaneous, increase entropy
5
Q
What does a positive deltaG value indicate?
A
Takes in free energy, anabolic, energetically unfavourable
6
Q
What reaction is energetically favourable?
A
Catabolic reaction (negative delta G)
7
Q
What reaction is energetically unfavourable?
A
Anabolic (positive delta G)
8
Q
What type of reaction increases entropy?
A
Catabolic
9
Q
What type of reaction is spontaneous?
A
Catabolic
10
Q
What are catabolic and anabolic reactions coupled?
A
Maintain a dynamic steady state of free energy flow.
11
Q
What type of reaction is exergonic and give an example?
A
Catabolic e.g hydrolysis
12
Q
What type of reaction is endergonic and give an example?
A
Anabolic e.g condensation
13
Q
Describe metabolism.
A
Chemical process, food used for tissue growth, catalysed by enzymes, intermediate metabolites, spontaneous reactions.
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.
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.
16
Q
Where does substrate level phosphorylation occur?
A
In cytosol and mitochondria.
17
Q
Where does oxidative phosphorylation occur?
A
Inner membrane of mitochondria.
18
Q
What is substrate-level phosphorylation?
A
Phosphorylates ADP from substrate to ATP using kinases.
19
Q
Give an example of substrate-level phosphorylation.
A
Glycolysis
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.
21
Q
what are the four major elements that construct human biomolecules?
A
C, H, O, N
22
Q
Explain why polarity of C-C bonds are crucial.
A
- C-C and C-H share electrons so stable.
- C-O, C-N, C-functional group highly polar so alter C-bond reactivity.
- C-C rotates freely
- C=C don’t rotate (rigid)
23
Q
What are the 5 kinds of chemical reactions?
A
- Redox (OILRIG)
- Making/Breaking C bonds
- Internal re-arrangements
- Group transfers
- Condensation and Hydrolysis
24
Q
Give an example of a redox reaction.
A
Glucose to 2 x pyruvate (glycolysis)
25
Give an example of making/breaking bonds.
Cleavage of glucose in glycolysis.
26
Give an example of internal re-arrangements.
Glycolysis (before glucose is split)
27
Give an example of group transfers.
Glycolysis (phosphate group transfer for ATP production)
28
Give examples of condensation and hydrolysis reactions.
All sub-units of proteins, polysaccharides and nucleic acids are Broken by Hydrolysis and Joined by Condensation.
29
Describe the structure of polysaccharides.
Polymers of sugar molecules linked by glycosidic bonds.
30
Describe the structure of proteins.
Polymers of AA monomers linked by peptide bonds.
31
Describe the structure of nucleic acids.
Polymers of nucleotide monomers linked by 3', 5'-phosphodiester bonds.
32
Describe the structure of lipids.
One or more long chain fatty acids with a carboxyl group and hydrocarbon fatty acid chain.
33
What structures are absent form prokaryotic cells compared to eukaryotic cells.
1. Nuclear membrane
2. Mitochondria
3. Membrane bound structures
34
What is the role of the nucleus?
Contains histone proteins, DNA, nucleoprotein and some RNA, enclosed by phospholipid bilayer.
35
What is the role of the rough ER and Golgi?
Central dogma i.e transcription and translation and role in protein modifications and transport.
36
What is the role of the lysosome?
Separate enzymes from rest of cell, used in autophagy or digestion of engulfed particles.
37
What is the role of mitochondria?
Matrix contains binding sites for calcium and enzymes for oxidation. Has it's own ribosomes and circular DNA so will self-replicate.
38
What are cilia and flagella?
Cell surface projections made of microtubules.
39
What is the role of the peroxisome?
Breakdown long chain FAs through beta-oxidation.
40
Describe the structure of the cell membrane.
1. Proteins embedded
2. Phospholipid bilayer (amphipathic)
2. Attached to cytoskeleton and ECM for cell-cell recognition
41
What is the role of the cytoskeleton?
Supports and maintains cell shape, holds organelles in position, moves organelles involved in cytoplasmic streaming.
42
What junctions can be found on the eukaryotic plasma membrane?
1. Anchoring
2. Gap
3. Channel forming
4. Adhesive (adherens - actin or desmosomes - keratin)
5. Tight
43
Name 5 functions of the cell membrane.
1. Signal transduction (by receptors)
2. Enzyme activity
3. Transport
4. Intracellular joining
5. Cell-cell recognition
6. Signalling (synaptic, endocrine, paracrine)
44
What is the cytoskeleton composed of?
1. Microfilaments (actin)
2. Intermediate filaments (fibrous proteins) and
3. Microtubules (tubular- alpha and beta sub-units).
45
Define hydrogen bond.
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
Are molecules that form H-bonds water soluble?
Yes.
47
What type of H bonds are angled?
Weak H bonds.
48
Describe the interactions between water molecules and solutes that determine solubility.
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
Describe amphipathic and give an example.
Contains hydrophobic and hydrophilic parts e.g phospholipids and proteins.
50
Define pH.
Expresses acidity or alkalinity on a log scale. pH = -log10C (c=H+ ions in moles/litre).
51
What equation relates the degree of proton dissociation of a weak acid to it's ionisation constant and the pH?
Henderson-Hasslebach Equation
52
What is the Henderson-Hassleback equation?
pH = pKa + log ([A-]/[HA])
53
What type of solution donates protons?
Acidic
54
What type of solution accepts protons?
Basic
55
What types of solutions fully dissociate?
Strong acids and strong bases (weak only partially dissociate)
56
Define buffer.
Weak acid which maintains optimal pH for optimal activity.
57
Give two examples of buffer systems in the human body.
1. Phosphate system (in cells)
| 2. Bicarbonate system (in plasma)
58
What equation can be used to check how much buffering capacity remains in patients with metabolic acidosis?
Henderson-Hassleback equation
59
Discuss the three main ways enzymes catalyse reactions.
1. Increase rate of spontaneous reaction
2. Decrease activation energy
3. Accelerate movement towards reaction equilibrium
60
What do enzymes NOT do?
1. Move reaction equilibria
| 2. Make a non-spontaneous reaction spontaneous.
61
What happens if substrate concentration is increased?
Increase initial rate of reaction.
62
Define 'Michaelis Constant'.
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
What does a larger Km suggest?
Less stable ES complex (less affinity enzyme has for substrate).
64
What does a smaller Km suggest?
More stable ES complex (more affinity enzyme has for substrate).
65
What is the Lineweaver-Burk plot used for?
To define Vmax and Km.
66
What does Km equal?
Rate at which ES is broken down/ rate at which ES is formed.
67
What equation is used to describe the hyperbolic curves?
Michaelis-Menten equation.
68
How can you predict the speed of the reaction (Vo)?
Vo = (Vmax+[S]/Km +[S])
69
Describe competitive enzymes.
Bind non-covalently and resemble substrate so competes for active site.
70
Describe non-competitive enzymes.
Bind non-covalently to another site (not the active site).
71
Compare Vmax and Km in competitive and non-competitive enzymes.
1. Competitive = high Km and unchanged Vmax
| 2. Non-competitive = unchanged Km and low Vmax
72
Describe allosterically-regulated enzymes.
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
Describe covalently modified enzymes.
- Reversible
- Regulate enzymes e.g protein kinases and protein phosphates and other proteins
- Example = Phosphorylation.
74
What lab test can be used to identify enzymes?
Electrophoresis.
75
Define isozymes.
Products of different genes but similar function.
76
Discuss use of enzyme assays in clinical diagnosis.
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
Describe the basic structure of the membrane.
- Thin bilayer of phospolipids (hydrophobic tails inside and hydrophilic head outside)
- Embedded with proteins (receptors, transporters, enzymes, associated peripheral membrane associated.
- Glycoprotein
- Glycolipid
78
What are the functions of membrane proteins?
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
Define diffusion.
Molecules spread from high to low concentrations until desired equilibrium reached.
80
Where can diffusion occur?
1. Through lipid bilayer
| 2. Through channels e.g aquaporins (molecules like glucose too large to pass through)
81
What are the two types of channels found on the cell membrane?
1. Voltage-gated (changes in membrane potential)
| 2. Ligand-gated (bind to chemical)
82
What is facilitated diffusion?
Use carrier mediated proteins and ATP to move AGAINST concentration gradient e.g Na+/K+ pump (3Na+ out and 2K+ in)
83
What factors favour diffusion through the lipid bilayer?
Small, uncharged, lipophilic (hydrophobic)
84
Define electrochemical gradient.
The ions creating the concentration gradient are charged particles therefore, an electrical gradient is created.
85
Explain carrier mediated transport systems.
Movement of molecules down an electrochemical gradient through transport proteins (facilitated diffusion).
86
Define osmolarity.
Number of osmoles of solute/litre (osmoles/L)
87
Define osmolality.
Number of osmoles of solute/kg of solvent (osmoles/kg).
88
What determines osmolarity?
Penetrating AND non-penetrating particles.
89
Define isosmotic.
Same total number of solute particles as ECF.
90
Define hypo-osmotic.
Fewer solute particles (must also be hypotonic).
91
Define hyper-osmotic.
Greater number of solute particles.
92
What determines tonicity?
Non-penetrating particles.
93
Describe the difference between isosmotic and isotonic.
```
Isosmotic = same number of solute particles as ECF.
isotonic = same number of non-penetrating solute particles as ECF.
```
94
Describe exocytosis.
Active transport of molecules out of cell using energy.
95
Name three types of endocytosis.
Phagocytosis, pinocytosis and receptor mediated (all forms of active transport in which cell transports molecules into cell).
96
Energetically unfavourable reactions can only proceed because?
They are couple to catabolic reactions.
97
The lipid membrane surrounding eukaryotic cells does not contain?
Ribosomes.
98
The lipid membrane surrounding eukaryotic cells does contain?
Carbohydrates, cholesterol, ion channels and receptors.
99
The dissociation constant of water is equal to?
1x10^14 (mol/L)^2
