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Medical Cell Biology and Genetics - Amino Acids and Proteins Flashcards

(12 cards)

1
Q

What is the chiral centre of an amino acid?

A

The central alpha carbon of an amino acid

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2
Q

How are amino acids classified?

A

According to:

  • polarity (how they reach with water at pH 7)
  • aromatic (contain benzene ring) or alipathic (no ring)
  • whether they are positively or negatively charged
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3
Q

What is a zwitterion?

A

A neutral molecule with both positive and negative charges
In the case of amino acids the amine group deprotonates the carboxylic group
NH3—-C—-COOH —> NH4+—-C—-COO-

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4
Q

What are the 3 key properties of the peptide bond?

A
  • all atoms are in the same plane
  • although it is a single bond it has double bond characteristics therefore does not rotate
  • the carbonyl oxygen and amide hydrogen are in the trans orientation
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5
Q

What is the isoelectric point of a protein?

A

The pH at which the protein has no overall charge
eg Acidic proteins may have negatively charged amino acids therefore have a low pI
eg Alkaline proteins contain many charged amino acids and have a high pI

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6
Q

Define the 4 levels of protein structure:

  1. Primary structure
  2. Secondary structure
  3. Tertiary structure
  4. Quaternary structure
A

Primary structure - the amino acid sequence
Secondary structure - folding of the peptide chain into alpha helices or beta pleated sheets
Tertiary structure - further folding to form the 3D structure of the protein
Quaternary structure - assembly of a large complex of MULTIPLE peptide chains eg Hb

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7
Q

List the bonds associated with each level of protein structure

A

Primary structure - peptide bonds
Secondary structure - hydrogen bonds
Tertiary structure - H bonds, van der waals forces, ionic interactions, disulfide bridges, hydrophobic interactions
Quaternary structure - same as above

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8
Q

In general what is the role of globular and fibrous proteins?

A

Globular proteins are mainly functional - such as enzymes and regulatory proteins eg Hb

Fibrous proteins tend to provide structure and support eg Collagen

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9
Q

What is the role of molecular chaperones?

A

Ensure that protein folding is correct, therefore preventing disease states due to inefficeint damaged proteins

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10
Q

What are the key features of the alpha helix ?

structure, and helix breakers and makers

A

Right handed helix
3.6 amino acids per turn

Pro acts as a helix breaker because the rotation around the N-C bond is impossible.
Gly acts as a helix breaker because the tiny H R group supports other conformations.

Small HPHOBIC amino acids are strong helix formers

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11
Q

Describe the structure and bonds of a beta sheet

A

Can be parallel - run in same direction
Can be antiparallel - run in opposite directions

There are lots of inter-strand hydrogen bonds

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12
Q

What is pK and how is it calculated?

A

NEED TO FINISH

pK = - Log [H+]

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