amino acids

Question 1

what is a protein

Answer 1

a polymer of amino acids

Question 1

what is the general formula for amino acids

Answer 1

NH2-CHR-COOH

Question 2

what does the NH2 represent in an amino acids

Answer 2

the amine group

Question 3

what does the R group represent in an amino acid

Answer 3

variable groups on amino acids

Question 4

what does COOH represent in an amino acid

Answer 4

carboxyl group

Question 5

what reaction occurs when you join 2 amino acids

Answer 5

condensation

Question 6

how forms when you join 2 amino acids

Answer 6

dipeptide

Question 7

what forms when you join many amino acids together

Answer 7

polypeptide

Question 8

what bond is formed between amino acids

Answer 8

peptide bond

Question 9

what are peptide bonds

Answer 9

covalent bonds and so involve the sharing of electrons

Question 10

what happens during a hydrolysis reaction

Answer 10

the addition of water breaks the peptide bonds resulting in polypeptides being broken down into amino acids

Question 11

what are the 4 levels of structure in proteins

Answer 11

primary
secondary
tertiary
quaternary

Question 12

what is the primary structure

Answer 12

the sequence of amino acids bonded by covalent peptide bonds
the DNA of the cell determines the primary structure of a protein by instructing the cell to add certain amino acids in specific quantities in a certain sequences
the primary structure is specific for each protein (one alteration in the sequence of amino acids can affect the function of the protein)

Question 13

what is the secondary structure

Answer 13

occurs when the weak negatively charged carboxyl group, CO-, interact with the weak positively charged amine group ,NH+, to form hydrogen bonds
there are two shapes that can form within proteins due to the hydrogen bonds
α-helix - occurs when the hydrogen bonds form between every fourth peptide bonds (between the oxygen of the carboxyl group and the hydrogen of the amine group)
β-pleated sheet - forms when the protein folds so that the two parts of the polypeptide chain and parallel to each other enabling hydrogen bonds to form between parallel peptide bonds

Question 14

what is the tertiary structure

Answer 14

further conformational change of the secondary structure leads to additional bonds forming between the R groups
- hydrogen bonds between the R group
- disulphide - only occurs between cysteine amino acids
- ionic - occurs between charged R groups
- weak hydrophobic interactions - between non-polar R groups

Question 15

what are disulphide bonds

Answer 15

strong covalent bonds that form between two cysteine R groups (only amino acid with a sulphur atom)
bonds are the strongest within a protein but occur less frequently and help stabilise the proteins
they are also know as disulphide bridges and are not broken down by high temperatures and pH changes

Question 16

what are ionic bonds

Answer 16

form between oppositely charged R groups - holds different parts of the polypeptide chain together and contributes to the structure of proteins
ionic bonds are stronger than hydrogen bonds
broken by pH changes - denature of enzymes

Question 17

what are hydrogen bonds

Answer 17

form between strongly polar R groups
these are the weakest bonds that form but are the most common as they form between a wide variety of R groups
broken by high temp and pH changes

Question 18

what are hydrophobic and hydrophilic interactions

Answer 18

several amino acids have uncharged R groups - Non-polar amino acids. they are not attracted to water = hydrophobic and tend to cluster together at the centre of the protein to exclude water molecules = HYDROPHOBIC INTERACTIONS
HYDROPHILIC amino acids tend to be found of the surface of proteins where they can interact with water molecules
HYDROPHOBIC & HYDROPHILIC interactions are relatively weak bonds

Question 19

how does the tertiary structure determine the function of a protein

Answer 19

a polypeptide chain will fold differently due to the interactions between the R groups
each of the twenty amino acids that make up proteins has a unique group and therefore many different interactions can occur creating a range of proteins and functions

Question 20

what is the quaternary structure

Answer 20

exists in proteins that have more than one polypeptide chain working together as a functional macromolecule e.g. haemoglobin
each polypeptide chain in the quaternary structure is referred to as a subunit of the protein

Question 21

globular proteins

Answer 21

molecules of a relatively spherical shape, which are soluble in water and often have metabolic roles within the organisms

Question 22

fibrous proteins

Answer 22

has a relatively long, thin rope-like molecules that are insoluble in water and metabolically inactive, often having a structural role with an organism e.g. in bones or tendons or in the walls of blood vessels such as arteries

Question 23

what is elastin

Answer 23

the skin contains a large amount of elastin fibres which help to make the skin supple and elastic. elastin is also found in the walls of arteries
elastin fibres stretch when blood pulses through the artery and then recoils in between pulses helping the artery to return to its normal shape
elastin molecules are long strands containing hydrophobic regions and strands are cross linked to each other

Question 24

what is keratin

Answer 24

Keratin is found in hair, fingernails and the outer surface of skin
extremely strong and insoluble in water
consists of long stranded molecules
contains a very high proportion of the amino acids cysteine - lots of disulfide bonds which contributes to the strength of the molecule

Question 25

what are 3 examples of fibrous proteins

Answer 25

keratin
elastin
collagen

Question 26

what is the function of fibrous proteins

Answer 26

structural

Question 27

what is collegen

Answer 27

we find collagen in tendons, which connect muscle to bones and in ligaments which connect bones to each other. Collagen is also found in the skin
collagen is a strong molecule due to its structure
the polypeptide chains in collagen wrap tightly together to form a triple helix
every third amino acid in collagen polypeptides is glycine - smallest R group of any amino acids allowing the collagen polypeptide to wrap very together around each other. as they wrap around each other a large number of hydrogen bonds form between the polypeptide which stabilises the quaternary structure of the protein
polypeptides are also joined together by strong cross links - no weak spots

Question 28

what is the tertiary structure of globular proteins

Answer 28

non-polar hydrophobic R groups are orientated towards the centre of the protein away from the aqueous surrounding and their polar hydrophilic R groups orientate themselves on the outside of the protein forming a spherical shape

Question 29

what does conjugated means

Answer 29

a protein that contains a non-protein chemical group such as a prosthetic group or cofactor

Question 30

what is a prosthetic group

Answer 30

a permanent non-protein part of a protein molecule

Question 31

what is an example of a prosthetic / conjugated group

Answer 31

haemoglobin which contains the prosthetic group called haem

Question 32

what proteins have prosthetic groups

Answer 32

globular proteins

Question 33

what is the structure of haemoglobin

Answer 33

conjugated protein - contains the prosthetic group haem (haem group with the Fe ion)
quaternary structure
4 polypeptides subunits = 2 alpha subunits and 2 beta subunits
found in red blood cells
each subunit contains the prosthetic group haem

Question 34

give 3 examples of globular proteins

Answer 34

haemoglobin
insulin
carbonic anhydrase

Question 35

what is the structure of insulin

Answer 35

hormone carried in the bloodstream and plays a role in blood glucose regulation
two polypeptide chains held together by 3 disulphide bonds (6 of these molecules bond together in the pancreas to create a large globular structure)
stored in secretory vesicles

Question 36

what is the structure of carbonic anahydrase

Answer 36

found in red blood cells
Zn2+ ion (prosthetic group) is held in position by 3 histidines
synthesised as a singly polypeptide from one gene (tertiary structure)

Question 37

what is the function of haemoglobin

Answer 37

transport oxygen in red blood cells + bind reversible to oxygen
binds to oxygen in the lungs and then it releases the oxygen in the body tissues
the haem group has the Fe 2+ ion which binds to oxygen molecules
each haemoglobin molecule can carry 4 oxygen molecules (8 oxygen atoms)

Question 38

what is the the synthesis and function of insulin

Answer 38

hormone (peptide) and synthesised by β-cells of pancreas
carry out functions by binding to specific receptor molecules - the receptors are proteins found on the cell membrane of target cells
red blood glucose - stimulated uptake of glucose and conversion into glycogen

Question 39

what is the synthesis and function of carbonic anhydrase

Answer 39

enzyme
carbon dioxide transport
reacts CO2 + H2O to form carbonic acid (CO2 transported as hydrogencarbonate ion in plasma

Question 40

why are globular proteins soluble in water

Answer 40

globular proteins have got hydrophilic amino acids on their surfaces
this means that the hydrophilic R groups can interact with water molecules making them soluble in water
globular proteins have got hydrophobic amino acids which are not attracted to water. in globular proteins, hydrophobic amino acids are found deep in the centre of the protein away from water molecules

Question 41

what are fibrous proteins insoluble in water

Answer 41

have a large proportion of amino acids with hydrophobic R groups