topic 2.4- proteins Flashcards
define denaturation
a change to the conformation of the protein
why does a denatured protein normal not return to its original structure?
denaturation is permanent.
why does heat cause denaturation?
it causes vibrations within the molecule that can break intermolecular bonds or interactions
why does change in pH cause denaturation?
the charges on R groups are changed, breaking ionic bonds within the protein or causing new Ionic bonds to form
what property of proteins usually changes after denaturation and why?
soluble proteins often become insoluble and form a precipitate; this is due to the hydrophobic R groups in the centre of the molecule becoming exposed to the water around by the change in conformation
how are amino acids linked together?
by condensation to form polypeptides
define a polypeptide
a chain of amino acids held together by peptide bonds; these are the main component of proteins
describe the condensation reaction to form polypeptides from amino acids
- involves the amino group (NH2) of one amino acid and the carboxyl group of (-COOH) of another
- water is eliminated
- peptide bond formed
how many different amino acids are there in polypeptides synthesised on ribosomes?
20
state the features that all amino acids have in common
a carbon atom in the centre of the molecule is bonded to an amine group, a carboxyl group and a hydrogen atom, as well as a variable R group
what allows for the huge range of possible polypeptides?
amino acids can be linked together in any sequence
for a polypeptide of n amino acids, there are ? possible sequences
20^n
what codes for the sequence of amino acids in a polypeptide?
genes- the base sequence that codes for a polypeptide is known as the open reading frame
a protein may consist of —-
a single polypeptide or more than one polypeptide linked together
what determines the three-dimensional conformation of a protein?
the amino acid sequence
what is the conformation of a protein?
its 3 dimensional structure
describe how R groups influence a protein’s solubility
soluble in water, there are hydrophilic R groups on the outside of the molecule and usually hydrophobic groups on the inside
give 12 functions of proteins in humans
- catalysis- enzymes to catalyse chemical reactions
- muscle contraction- actin and myosin cause contractions used in motion/transport in the body
- cytoskeletons- tubulin is the subunit of microtubules
- tensile strengthening- fibrous proteins give tensile strength needed in skin, tendons, ligaments and blood vessel walls
- transport of nutrients and gases- proteins in blood help transport O2, CO2, Fe and lipids
- cell adhesion- membrane proteins cause adjacent cells to stick to each other
- hormones- some such as insulin, FSH and LH are proteins
- receptors- act as binding sites in membranes/cytoplasm for hormones, neurotransmitters
- blood clotting- plasma proteins act as clotting factors to help blood go from liquid to gel
- packing of DNA- histones associated with DNA in eukaryotes, help chromosomes condense during mitosis
- immunity- antibodies
give 6 proteins that demonstrate the range of protein functions
- rubisco
- insulin
- immunoglobins
- rhodopsin
- collagen
- spider silk
rubisco
catalyses the reaction that fixes carbon dioxide from the atmosphere
insulin
hormone secreted by beta cells in the pancreas that signals to cells in the body to absorb glucose and help reduce the glucose conc in the blood
immunoglobin
antibodies- bind to antigens on bacteria/other pathogens
rhodopsin
one of the pigments that absorbs light for vision- membrane protein of rod cells of retina
collagen
1/4 of all the protein in the human body
- forms a mesh of fibres in skin/ blood vessel walls/ligaments that resists tearing
- also part of teeth and bones
spider silk
used to make the spokes of spiders’ webs
define a proteome
all of the proteins produced by a cell, tissue or an organism
what is the difference between the genome and the proteome of an organism?
whereas the genome of an organism is fixed, the proteome is variable because different cells in an organism make different proteins.
define a genome
all of the genes of a cell, tissue or organism
why does everyone have a unique proteome?
- because of differences in activity
- because of small differences in the amino acid sequence of proteins
