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Medicine - Year 1 > Infection and immunity - Biochemistry > Flashcards

Infection and immunity - Biochemistry Flashcards

1
Q

What are proteins?

A

Polymers of amino acids

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2
Q

List the functions of proteins

A
  • Structure
  • Metabolism
  • Gene regulation
  • Signalling
  • Development
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3
Q

Draw the basic structure of an amino acid and label the components

A
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4
Q

All amino acids occur as two isomers, D or L, except for one. Which amino acid is it?

A

Glycine

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5
Q

Describe the role of ribosomes

A

Protein biosynthesis machine

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6
Q

What is the roleof mRNA

A

Conatins information

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7
Q

What is the role of tRNA

A

Carries the amino acids

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8
Q

Describethe 3 stages of protein synthesis

A
  1. Initiation - Ribosome and initiation factors assemble at start codon AUG
  2. Elongation - Amino acids joined together to form a polypeptide
  3. Termination - By stop codons UAA, UAG, UGA on mRNA
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9
Q

What is the start codon?

A

AUG

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10
Q

What are the stop codons?

A

UAA, UAG, UGA

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11
Q

The genetic code is degenerate, universal and non-oberlapping. Explain what these terms mean

A

Degenerate - more than one triplet can code for the same amino acid

Universal - Amino acids are the same in all organisms

Non-overlapping - The genetic code is read as a triplet

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12
Q

What bond is formed between amino acis to form proteins? Decsribe how this happens

A

Peptide bond

Formed when amino acids are joined together in a condensation reaction and water is removed (from carboxyl and amine group)

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13
Q

The peptide bond is planar. What does this mean?

A

The atoms can arrange themselves around the central molecule. The rotation of adjacent peptidebonds is only allowed at N-C and C(central)-C

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14
Q

Name the hierachies of protein structure

A
  1. Primary structure
  2. Secondary structure
  3. Tertiary structure
  4. Quatenary structure
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15
Q

Describe the primary structure of proteins

A
  • Sequence of amino acids
  • It is determined by the DNA sequence
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16
Q

Describe the secondary structure of proteins including their bonding and their configuration

A

Alpha helix

  • Rod like structure: polypeptide chain tightly coilded, amino acid side chains extending outwwards from the helix axis
  • Stabilised by H-bonds: backbone amine (NH) and carbonyl (CO groups, 4 residues away aling th change
  • Configuration: right-handed (clockwise) coiled, 3.6 amino acids per turn

Beta-pleated sheet

  • Zigzag structure: C-C bonds are tetrahedral so cannot exist in planar configuration
  • Stabilisded by H bonds: backbone (NH) and carboxyl (CO) groups, between different parts of the chain or between different chains
  • Configuration: You can have parallel beta-sheet (polypeptide chain runs in the same direction) or Antiparellel beta-shhet (polypeptide chain runs in different directions)
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17
Q

Describe the tertiary structure of a protein,including the bonding and where these bonds may be found

A

Overall folding of the backbone, may be stabalised by these bonds:

  • Hydrogen - between side chains that have partial positive (δ + ) and negative (δ − ) charges, between
  • Ionic - between oppositely charged side chains
  • Disluphide bridges - between cystein residues
  • Hdrophobic interactions - in regions where there are large numbers of non-polar, aliphatic and aromatic side chains.
18
Q

a) What is a quaternary protein structure?
b) Describe the structure
c) Give an example of a quatenary protein structure

A

a) More than one polypeptide chain held together
b) Several sub-units held togteher by non-covalent bonds
c) Haemaglobin

19
Q

Describe the genetic error that causes sickle cell anaemia

A
  • Single point mutation in the DNA encoding beta-globin chain in Hb
  • The amino acid Gly in position 6 is replaced by Val
20
Q

List the type of proteins and provide exampls for each

A
  • Globular protiens - compact spheres e.g., haemaglobuin, albumin
  • Fibrous proteins - filamentous molecules e.g., collagen, keratin
  • Soluble protiens - dissolve in water e.g., haemoglobin, immunoglobulins
  • Membrane proteins - associated with memebrane e.g., glucose transport
21
Q

List the different types of membrane proteins

A
  • Integral protien with a single transmembrane helix
  • Integral protein with multiple transmembrane helix
  • Peripheral proteins with lipid anchors
  • Peripheral proteins attached to the membrane
22
Q

Describe the role of serum protein electrophoresis

A

Lab test that analyses proteins in blood

23
Q

How are serum proteins sepearted in serum protein electrophoresis

A
  • Serum proteins are seperated by their size and charge
24
Q

List the biological functions of enzymes

A
  • Part of metabloic pathways (glycolysis)
  • Signal transduction and cell regulation (kinases, phosphatases)
  • Digestion (amylases, proteases)
  • Movement (myosin)
  • Energy production (ATP synthase)
  • Drug metabolism (monooxygenases)
25
Describe the role of enzymes in disease and provide examples
* Drug targets - metabolic infections, infections e.g., angiotensin-converting-enzyme for treatment of blood hypertension * Diagnostic markers -acute conditions, chronic conditions e.g., Creatine phosphokinase for myocardial infarction * Inborn errors - Deficiency, reduced activity e.g., Clotting factor VII for haemophilia
26
Serum enzymes can be used inclinical diagnosis of disease. State the tissue source and diagnositc use of these enzyme: a) AST (aspirate mino transferase) b) ALT (alanine amino transferase) c) amylase d) CPK (creatine phosphokinase) e) GGT (gamma glutamyl transferase) f) LDH (lactatse dehydrogenase) g) Lipase h) Alkaline phosphatse i) Acid phosphatase
27
Describe the principle of enzymatic catalysis
1. Enzymes are catalysts 2. Enzymes cannot alter the equilibrium 3. Enzymes accelerate chemical reactions
28
Here is graph of reaction pofiile for enzymatic and non-enzymatic reactions. Describe the effect of an enzymatic reaction
* Lowere activation energy required to reach transitin state
29
State the Michaelis-Menten equation
v=(Vmax+[S])/(Km+[S])
30
What do the variables of the michaelis–Menten equation represent? v=(Vmax+[S])/(Km+[S])
V max = maximum reaction rate [S] = substrate concentration Km = measure for the stability of the enzyme-substrate complex (reflects the affinity of the enzyme for its substrate)
31
How can Vmax in Michaelis–Menten equation be estimated? v=(Vmax+[S])/(Km+[S])
It can be estimated from the plateau of the curve, where reaction rate is plotted against concentration
32
The Km in the Michaelis-Menten equation is a measure for the stability of the enzyme-substrate complex v=(Vmax+[S])/(Km+[S]) a) What does a large Km mean b) What doe a small Km mean?
a) Low-substrate enzyme affinity b) High-substrate enzyme affinity
33
What type of reaction does the Michaelis-Menten equation only apply for?
Reactions with a single substrate
34
Describe the Michaelis-Menten model
35
a) What are cofactors? b) What are organic cofactors known as?
a) non-protein substances required for an enzymatic reaction to proceed. b) Co-enzymes
36
Coenzymes can act as co-substrates or prosthetic groups. What does this mean?
Coenzyme as co-substrate - reversibly bound to enzyme Coenzyme as a prosthetic group - covalently linked with enzymes
37
State the energy transferred for the following co-enzymes a) ATP b) NADH/NADPH c) CoA
a) posphate b) electron c) acyl groups
38
a) What are trace elements? b) Provide one xamples of metal element and the enzymes they are associated with
a) Metal ions required by enzymes in order for them to corretly function b) Iron - cytochrome c oxidase, catalase, peroxidase
39
State the types of enzyme inhibiton that can occur
* Irrevesible * Reversible - competitive * Irreversible - non-competitive
40
a) What is competitive inhibition? b) What effect does this have on the Vmax and Km
a) Occurs when an inhibitor binds reversibly to the active site of the enzyme b) Causes an increase in the Km for the substrate (more substrate is required to saturate the enzyme). The V max remains unchanged
41
a) What is non-competitive inhibition? b) Describe the efffect this has on the Vmax and Km?
a) Non-competitive inhibition occurs when the inhibitor binds to a site other than the active site of the enzyme b) Because the binding of the substrate is unaltered, the Km remains unchanged. However, the V max decreases.
42
What is the Ki constant?
It an inhibitor constant. It is an indicator for how potent an inhibtor is and concentration required to prodce half maximum inhibition

Medicine - Year 1 (61 decks)

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