2.4 Proteins Flashcards
How do amino acids and polypeptides and proteins relate?
polypeptides are chains of amino acids which are formed by condensation reactions.
This happens on a ribosome via translation.
Proteins are mainly made out of one or more polypeptide. Some have other things too
condensation reaction between amino acids
involves an amine and carboxyl group an water is eliminated forming a peptide bond it requires an enzyme
dipeptide = two amino acids linked by peptide bond
polypeptide = many amino acids linked by peptide bond
how many amino acids do polypeptides have
if less than 20 are called oligopeptides
any number otherwise
insulin = 2
human tittin (part of muscle) = 34350
why are amino acids diverse
R group
20 types of amino acid
all have amine and carboxyl
some proteins are not in this basic 20 repetoire which is usually because the one of the 20 has been modified after the protein has been synthesized e.g. collagen when made has proline in many positions but this is converted to hydroxyproline to be more stable
diversity of amino acids
3 - r groups have rings
6 - r groups have no rings
9- r groups are hydrophobic (0-9 carbon atoms)
11 - r groups are hydrophilic
7 - r groups can be charged
4- hyrdophilic groups are polar but not charged
4 - r groups are like acid (give up proton and become neg charged)
3 - r groups act as a base and accept these protons and become positive charged
why do we only have 20 amino acids theories
- teh 20 were the 20 availible on earth when life evolved
- they are the ideal 20 for making the wide range of 20
- all life has one great grandfather which had these 20 and it is difficult for more different amino acids to evolve due to process of translation
how many possible polypeptides are there
the formula for a polypeptide with n amino acids is 20^n
why do genes have more codons than amino acids they code for
extra base sequence at both ends and at points in the middle
the base that codes for the polypeptide is the open reading frame which is a small proportion of total DNA
name proteins that have 1,2,3 and 4 polypeptides
- lysozyme, and enzyme in e.g. nasal mucus and years, kills some bacteria by digesting the peptidoglycan in cell walls
- integrin,membrane used to make connections between structures inside and outside cell, hydrophobic portion of Polypeptides in membrane, the two can be next to each other or apart like a folding knife
- collagen, structural protein in tendons, ligaments, skin and blood vessles, high tensile strength and limited stretch, rope like molecule so hihg tensile stregnth and small stretch allowed so less breakage
- hemoglobin, transport o2 in rbcs, binds o2 in lungs release on tissues with low o2 levels, has non-peptide structures, has disulphide bridges, nearly spherical, conjugated protein as has non peptide structure
what is a protein conformation?
its 3D structure
can be elongated with repeating structures or more globular
in globular the polypeptides are gradually folded and have stabilising bonds between r groups
in hydrophilic goublar proteins the hydrophilic r groiups are on the outside
membrane proteins have hydrophobic outsides to attract the inside of the membrane
in fibrous proteins no folding so elongated shape
how do proteins denature
the bonds between the r groups that stabilise the conformation of a protein can be broken and this causes the protein to change shape
denaturation is permanent
soluble –> unsoluble and precipitate
as hydrophobiv r groups in centre are exposed to water due to change in conformation
heat causes this as vibrations within molecule causes intermolecular bonds to break
proteins have different heat tolerances
e.g. microorganisms near volcanic activity live over 80 degrees - Thermus aquaticus, prokaryote lives in hot springs of yellowstone - used in bio tech
extreme ph cause denaturation - changes charges on r groups, breaks ionic bonds in proteins or cause new ionic bonds to form
exception - pepsin works in stomach at ph of 1.5
the functions of proteins (13)
- catalysis - enzymes to catalyse reactions
- muscle contraction - actin and myosis for locomotion and transport in body
- cytoskeleton - give animals shape and size, mitosis need micortubules (subunit tubulin )
- tensile strengthening - skin, tendons, ligaments, blood vessle walls need tensile strength from fibrous proteins
- blood clotting
- transport of nutrients and gases in blood
- cell adhesion between cells in animal cells
- membrane transport - faciliatated diffusion, active transport, electron transport for PS and R
- hormones - some (insuline FSH LH) are proteins
- receptors - binding sites in membranes and cytoplasm for hormones, neurotransmitters, smells, taste, light
- packing DNA - histones
- immunity - making antibodies
bio tech uses - enzymes to remove stains, make insulin, monoclonal antibodies for pregancy tests, treating diseases
describe the functions of 6 important proteins
Rubisco - ruibulose biphosphate ccarboxylase, catalyses reaction that fixes CO2 from atmosphere, source of carbon for living organisms, most abundant protein, in leaves
insulin - signal to absorb glucose and reduce glucose blood conc, secreted by beta cells in pancrease to blood,globular so good for transport, has disulphide bonds, small so easy to transport
immunoglobin - antibodies, ;sites on tips of two arms that bind to antigens on bacteria or pathogens, other part can cause response e.g. acting as a marker to phagocytes that can engluf pathogens, these binding sites are hypervariable, each disease has own antigens
collagen - rope like protein, 3 polypeptides, nmany types, 1/4 of human bodies proteins is this, forms a mesh of fibres in skin and blood vessle that resist tearing, bundles of parallel collagen give strength to ligaments and blood vessels, prevents cracks and fractures in teeth and bone, long strnads, insoluble, chains linked by strong covalnet bonds
see also keratin, actin/myosin
spider slik - dragline slik stronger than steel and tougher than kevlar, used by spiders, when first made has regions of parralel polypeptides and other disordered tangle regions, but when silk is stretched tangles extend to slik is extendable and resistant to breaking
rhodopsin - vision depends on pigment that absorbs light e.g. rhodopsin, a membrane protein of rod cells in retina, made of a light sensitive retinal molecule, not amino acids, surrounded by opsin polypeptide. When single photon of light is absorbed it changes shape so opsin changes so nerve impulse is sent to the brain, low light is dected to
what is a proteome
all the proteins produced by a cell tissue or organism
to find out how many different proteins are produced mixtures of proteins are extracted, seperated by gel electophoresis.
antibodies with fluroscent marker added so if cell fluoresces protein is present
proteome is variable not fixed like genome as differenet cell to cell and time period to time period
proteome is unique to individual, except identical twins which can become different with age
what are the four different types of protein structures?
primary structure
affects how to protein will behave in water
polypeptide chain
finite number of amino acids affected by sequence of genes
secondary structure - some stay here
can have beta pleated sheets
or alpha helix (3 1/2 amimo acids per turn)
or both
depends on r group, both use h bonding between the amine and the C=O
tertiary structure
if in water based solution hydrophilic on outside
globular proteins
uses
- h bonds
- disulphide bridges
- ionic bonds
- hydrophobic / philic interactions
forms active site as makes the shape –> affected by change in amino acids
quaternary structures
most complex (hamolglobin, insulin, collagen)
2 or more polypeptide changes combined
often have non protein group
what bonds hold proteins together
- hydrogen bonds
- disulphide bridges - r group needs sufur
- ionic bonds
- hydrophilic.phobic interactions
