Biological Molecules - Proteins

Question 1

Define Amino Acid

Answer 1

An organic compound - contains both an amino group and a carboxyl group
Monomer of protein molecules

Question 2

Define Amino Group

Answer 2

NH2
Functional group in amino acids
1 atom nitrogen attached covalently to 2 atoms of hydrogen - leaves a lone valence e- on the nitrogen which is available for bonding to another atom.

Question 3

Define Carboxylic acid Group

Answer 3

COOH
Functional group in amino acids
1 carbon atom covalently bonded to 2 oxygen atoms. 1 oxygen atom covalently bonded to hydrogen atom. 1 valence e- on carbon available for bonding to another atom to carboxyl group can form part of larger molecule.

Question 4

Collagen

Answer 4

Most common Structural FIBROUS protein found in:
- connective tissue
- bones
- skin
- cartilage

extremely strong - fibres have tensile strength COMPARABLE TO STEEL
3 polypeptide chains - each up to 1000 amino acids long
repeating sequences of glycine w two other amino acids
3 alpha helixes arranged in a TRIPLE HELIX - held together by many hydrogen bonds
Collagen molecules found in fibrils held together to form collagen fibres
Collagen fibres combined w bone tissue

Question 5

Condensation

Answer 5

Chemical reaction where 2 molecules joined together by means of covalent bond to form LARGER molecule - at the same time a WATER MOLECULE is RELEASED.

Question 6

Dipeptide

Answer 6

Molecule consisting of 2 or more amino acids joined by PEPTIDE bond.

Question 7

Disulphide bridge

Answer 7

between 2 sulphur atoms
forms during cross-linking of the amino acids during protein synthesis
Disulphide bonds can be broken by a REDUCING AGENT

Question 8

Fibrous Protein

Answer 8

Protein w relatively long + thin structure
INSOLUBLE in water
metabolically INACTIVE
often has a STRUCTURAL role

Question 9

Globular Protein

Answer 9

have relatively SPHERICAL molecules
SOLUBLE in water
often have METABOLIC roles in organisms

Question 10

Haemoglobin

Answer 10

GLOBULAR Protein which carries oxygen in RBCs - a conjugated protein asw

4 polypeptide chains held together by DISULPHIDE BONDS - 574 amino acids in total
Each chain arranged around iron-containing haem group.
Iron enables haemoglobin to bind to and release O2 molecules.
Arrangement of the polypeptide chains determine how easily oxygen binds/is released.

Question 11

Hydrogen Bond

Answer 11

WEAK bond formed when partially positively charged groups come close to partially negatively charged groups.
Seen in water molecules + the secondary and tertiary structure of proteins.
form btwn amino acids w Strongly Polar R groups. Individually weak, collectively strong.

Question 12

Hydrolysis

Answer 12

Reaction in which molecule broken down into 2 SMALLER molecules by the ADDITION of a WATER MOLECULE + the BREAKING of a COVALENT bond.

Question 13

Hydrophobic

Answer 13

Water-repelling

Question 14

Hydrophilic

Answer 14

Water-loving(dissolve in water) - usually polar

Question 15

Ionic Bond

Answer 15

Attraction btwn opp charged molecules
Form btwn R groups which have IONISED AMINE AND CARBOXYLIC ACID groups - asparagine + aspartic acid
Easily broken by pH changes
Stronger than hydrogen bonds, weaker than disulphide bridge

hydrogen bond < ionic bond < disulphide bridge

Question 16

Peptide

Answer 16

Molecule consisting of small num of amino acids which are bonded together by PEPTIDE bonds

Question 17

Peptide Bond

Answer 17

Covalent bond which is formed when amino acids joined in a CONDENSATION reaction

Question 18

Polypeptide

Answer 18

Polymer consisting of many amino acid monomers which are covalently bonded together

Question 19

Primary structure

Answer 19

The sequence of amino acids found in a protein molecule/polypeptide chain

Question 20

Protein

Answer 20

Polymer consisting of many amino acid monomers covalently bonded together

Question 21

Quaternary Structure

Answer 21

Protein Structure where protein consists of MORE THAN ONE polypeptide chain
e.g. Haemoglobin + Insulin

Question 22

R-group

Answer 22

Side chain of amino acid
Structure of R group decides amino acid special properties

Question 23

Secondary Structure

Answer 23

Coiling/folding part of the protein due to formation of hydrogen bonds.
Alpha Helix
Beta-pleated Sheets

Question 24

Tertiary Structure

Answer 24

Overall 3D shape of the protein molecule in WATER.
Held together by bonds between R groups.
Result of interaction btwn parts of the protein: hydrgoen bonding, disulphide bridges, ionic bonds + hydrophobic interactions when in water/a cell.

Question 25

how many naturally occurring types of amino acids are there?

Answer 25

20 diff types

Question 26

What elements make up proteins?

Answer 26

Carbon, Hydrogen, Oxygen, Nitrogen(some contain Sulphur)

Question 27

What are the functions of proteins?

Answer 27

• Enzymes
• Hormones
• Structural Proteins
• Haemoglobin - binds to oxygen
• Antibodies

Question 28

What is the structure of an amino acid?

Answer 28

All amino acids have same basic structure.
Central carbon atom which forms bond w 1 carboxyl group + another bond w hydrogen group + third bond w amino group + fourth bond w any of a whole range of groups(R groups)
H R O
| | ||
N_____C_____C
| | |
H H O__H

Glycine R Group = H —– formula = CH2NH2COOH
Cysteine R Group = CH2__SH

Question 29

Where does protein synthesis occur?

Answer 29

In ribosomes in the cell

Question 30

How does a peptide bond form?

Answer 30

In ribosomes:
The amino acids are brought closer together and react to form a peptide bond
Peptide bonds = V Strong - involve covalent bonds(sharing of electrons)
Formation of Peptide bond happens through CONDENSATION REACTION - Hydrogen and Oxygen atoms are released to form a water molecule which is RELEASED

Question 31

How are proteins formed in plants?

Answer 31

Plants can manufacture the amino acids which they need.
Nitrate obtained from soil –> amino acids then bonded to organic groups which are made from products of P/SYN

Question 32

How are proteins formed in animals?

Answer 32

Animals take in proteins from diet –> preoteins digested into amino acids

Essential amino acid = CANNOT be built from materials taken into body can only be obtained from diet - mostly found in MEAT

Animals CANNOT STORE EXCESS AMINO ACIDS - amino group makes the amino acids toxic - amino acids are REMOVED THROUGH DEAMINATION in liver.

Question 33

How do we test for proteins

Answer 33

BIURET Test: used to determine the presence of peptide bonds in the protein
Add Sodium Hydroxide and then Copper Sulphate.

If test positive:
Solution turns from BLUE to Violet/Purple then the Proteins are present.
Solution turns from BLUE to PINK then peptides(short chains of amino acid/residues) are present.

If test negative:
No change - Biuret solution stays BLUE - no protein present

Question 34

Where do hydrophobic interactions occur in the tertiary structure?

Answer 34

Occur btwn NON-POLAR R Groups of amino acids. Such R groups tend to be clustered in the CENTRE of the protein molecule.

these R groups fold away from water - towards inside of protein – when in cell

Question 35

Where are the hydrophilic R groups found in proteins

Answer 35

On the OUTSIDE of GLOBULAR PROTEINS

attracted to water - these R groups fold towards the water