ch3 - amino acids and proteins

what are amino acids and what are proteins

amino acids are monomers that join to form the polymer proteins

what is the general structure of amino acids on the sides and middle

amine group = NH2

carboxyl group = COOH

middle = variable R group, C and H

what does it mean by a variable R group

there are 20 different possible R groups which means there are 20 different possible amino acids

what is another name for the R group

side chain

what is a peptide

when two or more amino acids are joined together by peptide bonds

how does a peptide form and what by-product is formed as a result

OH (on carboxyl group of one amino acid) reacts with the H (on amine group of another amino acid) forming a peptide bond which joins them together

> undergoes a condensation reaction which forms H2O as a by-product

how can peptide bonds be broken

hydrolysis reaction

by adding water it breaks peptide bonds which releases individual amino acids

what is a dipeptide

consists of two amino acids joined by one peptide bond

what is a polypeptide

consist of many amino acids joined together by multiple peptide bonds - forming a chain

what is the primary structure and why is it so important for the final protein produced

the sequence of amino acids in the polypeptide chain

> the order in which amino acids are specifically in is determined, coded by information in DNA

importance = the primary structure determines final 3D structure and function of a protein

if a mutation occurs in DNA what impact can it have on the primary structure

> doesnt always have an impact because different codons (different combinations of triplet of bases) can code for the same amino acid

> if it does have impact it will change the order amino acids are organised in the polypeptide changing the final 3D structure and function

what is the secondary structure

when the polypeptide chain is folded into an alpha helix OR beta pleated sheet depending on the sequence and order of amino acids

what bonds form in the secondary structure

hydrogen bonds will form between the CO (on carboxyl group of one amino acid) and the H (on amine group of another amino acid)

why is it that these hydrogen bonds can form between amino acids in the same polypeptide chain

because now that the polypeptide chain is folded into either alpha helix or beta pleated sheet the amino acids are close to each other

what is the tertiary structure and how many interactions can be involved to hold it together

when the alpha helix OR beta pleated sheet folds into 3D structure which are held by 4 possible interactions between the R groups of different amino acids

name the 4 possible interactions that can form between the R groups of different amino acids

-weak hydrogen bonds between polar (slightly charged) R groups

-strong ionic bonds between charged (+ve or -ve charged) R groups

-strong covalent disulphide bridges ONLY between R groups of an amino acid that contains sulphur, ONLY cysteine

-hydrophobic and hydrophilic interactions

» hydrophilic = turns out to interact with water

» hydrophobic = turns inside into the center, away from water

what is the quaternary protein

only formed by large proteins where multiple polypeptide chains are linked together by the 4 possible interactions in the TS

in the quaternary structure do the 4 possible interactions form between R groups in = same polypeptide chain OR different polypeptide chains

between R groups of amino acids in different polypeptide chains

what is the difference in number of polypeptide chains in tertiary proteins and quaternary proteins

tertiary = ONLY 1 polypeptide chain

quaternary = MULTIPLE polypeptide chains

what is a globular protein

a polypeptide chain which rolls up into sphere or globe shape

are globular proteins soluble or insoluble in water and why

soluble - they have hydrophilic polar R groups on the outside and hydrophobic non polar regions on the inside

name a useful property of globular proteins

compact

name 3 functions of globular proteins

enzymes, hormones, antibodies

state example of a globular protein and explain (what its made of, produced by and how it operates to carry out its function)

insulin

-a hormone made of 2 polypeptide chains

-produced by beta cells in the pancreas, its specific 3D shape is complementary to receptors on cell surface membrane of liver and muscle cells enabling it to lower BGL

what is a conjugated protein

a type of globular protein which contains a prosthetic group (nonprotein component)

state two examples of conjugated proteins

haemoglobin

catalase

explain what haemoglobin is made of and how these components enables it to carry out its function

haemoglobin

-quaternary protein made up of 4 polypeptide chains: 2alpha and 2beta

-each polypeptide chain has a prosthetic haem group which contains Iron II

>Iron II atoms can reversibly bind to 1 O2 molecule hence each haemoglobin can carry 4 O2 at a time

(4polypeptide chains = 4 haem groups = 4 O2 molecules) enabling transportation of oxygen around the body

explain what catalase is made of and how these components enables it to carry out its function

catalase

-enzyme, its a quaternary protein which consist of 4 polypeptide chains

-each polypeptide chain has a prosthetic haem group which contains Iron II

>Iron II atoms bind to hydrogen peroxide to break it down into oxygen and water

(4polypeptide chains = 4 haem groups) enabling catalysed breakdown of hydrogen peroxide since its toxic when it accumulates in the body

what is a fibrous protein

polypeptide chain which forms a long twisted strand

are fibrous proteins soluble or insoluble in water and why

insoluble - due to high proportion of exposed non polar R groups

> non polar molecules are insoluble in water since they cannot form H bonds with water

name a useful property of fibrous proteins

stable structure

state a function of fibrous proteins

their strength enables them to provide structural support

state 3 examples of a fibrous proteins

keratin

elastin

collagen

explain where keratin is found, why its important and a component which enables it to carry out its function

found in skin, hair, nails - important as it protects the body

it has large number of amino acid cysteine allowing many strong disulfide bonds to form creating a strong and insoluble material

explain where elastin is found and why its important

found in elastic fibres in alveoli and blood vessels - veins and arteries

it is elastic which is important as it enables these structures to stretch and recoil from their original shape which prevents bursting

explain where collagen is found and a component which enables it to carry out its function

found in bone and muscle

has triple helix structure which provides high tensile strength