2- amino acids and peptides

Question 1

What are amino acids

Answer 1

Building blocks of peptides ( which make proteins )

Question 2

Number of amino acids in the body that make up proteins

Answer 2

20

Question 3

Components of an amino acid

Answer 3

Amine group ( NH2)
Carboxyl group COOH
Side chain (R)
H 
Central C

Question 4

Stereoisomers of amino acids

Answer 4

Can form L or D stereoisomers
Groups can be arranged in 2 ways
Only the L isomer is found in amino acids that make up proteins

Question 5

How can amino acid side chains affect their properties

Answer 5

Some amino acid chains are negative, positive or uncharged polar making the amino acid polar and hydrophilic ( OXYGEN, POLAR OR NITROGEN ATOMS )

Some side chains are non polar = amino acid is non polar and hydrophobic ( water hating )

Question 6

Naming amino acids

Answer 6

Often have a full name, one letter name and 3 letter

1 letter may be first letter OR another letter

Question 7

Peptide bonds

Answer 7

AA join together into chains via peptide bonds
Carboxylic and amino group
COVALENT BOND between carbon of carboxyl group and nitrogen of the amine group of second AA
Loose one oxygen and hydrogen from carboxyl and 1 hydrogen from amino group ; h20

Question 8

Condensation reaction

Answer 8

FORMING product 2—1
Making bonds
Loosing water

Question 9

Hydrolysis reaction

Answer 9

BREAKING DOWN 1—2
Breaking bonds
Using water

Question 10

Peptide

Answer 10

Many AA joining via peptide bonds

Question 11

Polypeptide

Answer 11

many amino acids

Question 12

Dipeptide

Answer 12

2 amino acids

Question 13

Tripeptide

Answer 13

3 amino acids

Question 14

Some peptides are directional

Answer 14

DIfferent ends

Question 15

Insulin peptide

Answer 15

2 different peptide chains - a chain and b chain

2 chains attached by disulphide bonds ( covalent ) on side chain of cysteine amino acids

Question 16

As pH increases, charge on peptide

Answer 16

DECREASES

Question 17

As pH decreases, charge on peptide

Answer 17

INCREASES

Question 18

Protein folding
whats it based on
how ?

Answer 18

Proteins must fold into their correct 3d shape to function
Protein folding is based on : hyrogen bonds, electrostatic (ionic) bonds, van der waals forces, hydrophobic and hydrophilic interactions

Hydrophobic /non polar regions of the protein fold in on themselves so they’re protected from the water

Fold into most stable conformation

Determined by sequence of AA present

Question 19

Protein structure ?

Answer 19

To suit the proteins function

Question 20

Collagen

Answer 20

Rigid and strong
3d shape
rope like
3 strands twisted

Question 21

Elastin

Answer 21

Stretchy
Helps to make skin stretchy and retain form
Elastin made up of short pieces of polypeptide which are cross linked, individual protein molecules stretch but cross links keep everything in ordered form

Question 22

Enzymes

Answer 22

Specific active site that fits their substrate

Question 23

Primary level of protein structure

Answer 23

Sequence of amino acids
Determined by sequence of nucleotides in the gene that codes for that protein
Each 3 nucleotides in the gene ( codon) codes for a particular amino acid
Gives them their unique function

Question 24

Secondary level of protein structure

Answer 24

Regular repeating structure like alpha helix and B sheet
Way that polypeptides are coiled
Stabilized by H bonds between C=O and N-H, non covalent

Question 25

Alpha helix

Answer 25

Hydrogen between carbonyl group and NH group, tight coil/helix stabilizes helix structure, allows for tight coiling so the O and H are near each other for bonding

R groups face outwards so they can interact with other parts of the protein

Question 26

Beta sheet

Features of antiparallel sheet

Answer 26

Stabilized by hydrogen bonds, parallel ( when both strands run in the same direction ) or anti parallel ( when 2 strands run in different directions )

In antiparallel, atoms align better meaning hydrogen bonds are more perpendicular and align more easily = MORE STRONG

Question 27

Beta turns

Answer 27

IN BETWEEN beta sheets 
Turns polypeptide to the next strand 
Stabilized by hydrogen bonds 
From the carbonyl to NH group 
3 aa in between - bends back on itself

Question 28

Tertiary structure

Answer 28

Folding into 3d shape
Hydrophobic amino acids buried in the centre, away from water ( hydrophobic effect) with hydrophillic amino acids on the outside , integrating with water

Question 29

Quaternary structure

Answer 29

Arrangement of several polypeptides in a protein complex

Each polypeptide chain in protein complex is known as a subunit

Question 30

Dimer

Answer 30

2 subunits in a protein complex

Question 31

tetrameter

Answer 31

4 subunits in a protein complex

e.g. haemoglobin ; 2 beta and 2 alpha , each bound to haem group

Question 32

Effect of Protein misfolding

Answer 32

Loss of activity
Degradation by lysosomes or proteasomes
BUT if theres too much misfolded protein in a cell - aggregation ( stick together ) to form amyloid fibres, which can lead to neurodegenerative diseases e.g. alzeihmers