proteins

how do they differ from lipids and CH

in addition to C, H and O always contain N and many also contain S and some contain P

what are proteins

polymers made of amino acid monomers

polypeptide

chains of amino acids

amino acids

all have the same basic structure

Be able to draw the general formula for amino acids

basic structure of amino acids

attached to a central carbon atom :

an amino group- NH2 at the N terminal of the molecule

a carboyl group COOH at the C terminal of the molecule

a hydrogen atom

the R group

the R group

is different in each amino acid

at ph7 which is the ph of the cell

the amino group gains an H and becomes positively charged

the carboxyl gorup looses an H and becomes acidic

therefore at ph 7

an amino acid has both a postive and a negative charge —> zwitterion ions

forming bonds

the amino group of one amino acid reacts with the carboxyl group of another amino acid with the elimination of water

forming

a peptide bond and the resulting compound is a dipeptide

type of reaction

peptide bond

the chemical bond formed by the condensation reaction between the amino group of one amino acid and the carboxyl group of another

there are

20 different amino acids used to make up proteins so there are thousands of different proteins and their shape is determined by the specific sequence of amino acids in the chain

primary structure

order of amino acids in a poylpeptide chain determined by the base sequence on one strand of the DNA molecule

this is because

there are 20 DAC that can be joined in any order and combination so there is huge number of possible polypeptides

secondary sturcture

the shape that the PP forms as a result of hydrogen bonding between the O on the carboxyl groups and the H on amino gorups in the peptide along the chain

this is because

this bonding causes the long PP to be twisted into a 3D shape

type 1

spiral shape- alpha helix : protein keratin has a high proportion of alpha helix

the second type

beta pleated sheet which is a less common arrangement: the protin fibroin in silk has a high proportion of beta pleated sheet

teritary sturcture

when the alpha helix of the secondary protein structure can be folded and twisted to give a more complex compact 3D s structure

what is the shape maintained by

hydrogen bonds

ionic bonds

disulphide bonds

hydrophobic interactions (what cause the.. watch the vid mate)

these bonds

are i

quaternary sturcture

some PP chains combine with another PP chain becaue some are not functional unless they are in combination

another possibility

they may be associated with non protein groups and form large complex molecules such as haemoglobin

for example

the insulin molecule which has two chains

shapes

the role of proteins depend on their molecular shape

type 1

fibrous proteins which have long thin molecules and their shape makes them insoluble in water so they have structural functions as in bone

example 1 of fibrous proteins

keratin the protein in hair, the pp are in parallel chains or sheets with many cross linkages forming long fibres

example 2

collagen, fibrous proteins are strong and tough providing strength and toughnenss needed in tendons

describe the structure of collagen

a single fibre (tropocollagen) consists of three identical PP chains twisted around each other like a rope and the chains are linked by hydrogen bonds making the molecule very stable

type 2 of proteins

globular proteins which are compact and folded into spherical molecules making them soluble- metabolic functions

example

haemoglobin consisting of 4 folded PP chains at the centre of each of which is the iron containing group haem

Identify amino acids given a structural formula and r group

how to test a sample of a solution for protein

add of few drops of buiret reagent (NaOH and CuSO4)

what happens

the NaOH and CuSO4 react to make blue CuOH which interacts with the peptide bonds present in the protein to make biuret which is purple

concentrations

at low protein concentrations- the colour change is difficult to detect by eye , the more concentrated the darker the purple colour

type of test

qualitative but could be used as a semi quantitative comparing the intensity of purple in two identically treated solutions

greater accuracy

measuring the absorbance of the purple biuret in a colorimeter using a yellow filter gives an estimate of relative concentration of proteins present in a sample but to detect the concentration of a specific protein a biosensor is used

STEPS OF PROTEIN TRAFFICKING

Transcription of DNA to mRNA

mRNA formed leaves nucleus to one of the ribosomes on the RER

In ribosome translation of mRNA to form a polypeptide

Protein made on ribosomes enter RER and travels through the membrane bound sacs of the ER

STEPS OF PROTEIN TRAFFICKING

As the protein passes through the ER it is processed and assumes 3-dimensional shape

When the protein reaches the end of the ER sac a vesicle containing her protein is pinched off the ER sac

Steps for protein trafficking

The transport vesicles from RER move material from the ER to Golgi apparatus , they fuse to form flattened sacs of the Golgi apparatus

When the vesicles reach the Golgi apparatus the vesicles fuse with the Golgi apparatus on the receiving face proteins are then modified within the Golgi apparatus

Steps

Vesicles containing modified proteins are pinch off the Golgi apparatus

They then fuse with the cell surface membrane and release their contents releasing proteins by exocytosis

Examples of globular proteins

Enzymes, antibodies, plasma proteins and hormones