proteins Flashcards
what is the most basic form of a protein/ what is the monomer of protein
amino acid
how does a polypeptide become functional
it must be folded
what happens to a polypeptide if it is folded wrong?
it will be dysfunctional
list 6 functions of proteins
support, enzymes, transport, defense, contraction, regulation
explain how proteins are used for support
some proteins have a rigid structure and can be used in the cell/body for structural support, i.e keratin in hair or fibrin in clots
write a short note about enzymes
biological catalysts, substrate -> product, active site/cleft, specific, globular
explain how proteins can be used in transport
membrane proteins allow transport of substances in and out of the cell (aqueous substances cannot pass through the lipid bilayer and so pass through protein channels). carrier proteins can close around a molecule, flip, and release it to the other side of the cell membrane
what is the purpose of haemoglobin
transports oxygen
what is the purpose of myoglobin
transports oxygen to muscle
what is the purpose of transferrin
transports iron
how many polypeptide chains can a protein have
one or more
how many polypeptide chains does a red blood cell have
4 (with binding sites)
explain how proteins aid with defense
antibodies are proteins which can detect foreign cells/substances and alert the defense system
give 3 examples of protein contractions
muscle fibres, cilia, spindle fibres
what is actin and myosin
two protein filaments which aid muscle contraction (sliding action)
how do proteins help with regulation in the body
hormones are inter-cellular messengers that influence the metabolism of cells, i.e insulin regulates blood glucose levels
what bio-molecule is insulin made of?
protein (all hormones are proteins)
what is the monomer of protein?
amino acids
name the 4 groups the central carbon in an amino acid is bonded with
a hydrogen atom (-H), an amino group (NH2), a carboxyl group (COOH), a side chain (-R)
draw the basic structure of an amino acid and include: a hydrogen atom (-H), an amino group (NH2), a carboxyl group (COOH), a side chain (-R)
how can the 20 distinct amino acids be distinguished?
by the R group/chain (variable side chain)
define hydrophobic and hydrophillic
hydrophobic- water hating, hydrophillic- water loving
what are the features of hydrophobic amino acids?
repel aqueous environment, reside usually on the interior of proteins, do not ionise (ionic bond formation) or participate in hydrogen bonding
what are the features of hydrophillic amino acids?
interact with aqueous environment, often involved in hydrogen bond formation, are found on the exterior surfaces of proteins
what is a zwitterion?
an amino acid with no ionisable R group with a neutral electric charge and a pH of 7.4
draw a zwitterion
what happens if you increase the pH of a solution of an amino acid by adding hydroxide ions (OH-) to a zwitterion
the hydrogen ion is removed from the NH3+ group and water is formed
what happens if you decrease the pH by adding an acid (H+) to a solution of an amino acid
the -COO- part of the zwitterion picks up a hydrogen ion and becomes positive
what is the isoelectric point (pI)
when the net charge of an amino acid/protein is zero
what are the 5 chemical classes of amino acid R groups?
- non-polar and aliphatic. 2. aromatic (generally nonpolar) 3. polar but uncharged. 4. neg charged. 5. pos charged
what are the features of nonpolar alliphatic R groups
the hydrocarbon groups are nonpolar and hydrophobic, usually located on the interior of the protein, no pos or neg poles are formed due to it being nonpolar
what are the features of the polar + uncharged class of R groups
the hydrocarbon R groups are polar (electron distribution is uneven- they will interact with other elements in a solution) and hydrophillic. located on the exterior of the protein,
what are some features of aromatic R groups
an amino acid which has an aromatic ring, are very hydrophobic
features of positively charged R groups
are positively charged at physiological pH, are not in zwitterion formation, are hydrophillic
features of negatively charged R grouos
have a negative charge, have carboxyl groups in R side chains, negatively charged at physiological pH, hydrophillic
what is a peptide bond + how is it formed?
a covalent bond (sharing of electrons) formed between two amino acids when the a-carboxyl group of one and the a-amino group of the other undergo a condensation dehydration reaction losing a water molecule
is the R chain involved in a condensation dehydration reaction?
no- the reaction is only between carboxyl and amino groups
what sort of bond is a peptide bond
a covalent bond (electrons are shared)
what is the reaction called that involves the creation of a peptide bond and the loss of a water molecule
condensation dehydration reaction
is the R side chain involved in a condensation dehydration reaction
no
draw the formation of a peptide bond
which groups do peptide bonds form between
carboxyl group of one amino acid and the amino group of another
define polypeptide
the amino acid structure of a single chain
define peptide
two or more amino acids joined together by peptide bonds
what effect does the final shape have on a protein
it determines its function
how many levels of structure are there in a protein?
4
list the 4 protein structure levels
primary, secondary, tertiary, Quaternary
what is the primary structure of a protein?
the specific sequence of a amino acids joined together via peptide bonds
what does every polypeptide begin and end with
free amino group (N-terminus) and ends with free carboxyl group (C-terminus)
what is the secondary structure of a protein?
the local folding of chains into regular patterns (either alpha helix or beta pleated sheets)
what bond is involved in alpha helix and beta pleated sheets?
hydrogen bonds- forms between the carbonyl O of one amino acid and the amino H of another
how do alpha helix proteins fold?
hydrogen bonds form between the carbonyl C=O and amino N-H groups 4 amino acids down the chain. this pulls the polypeptide into a helical shape that resembles a coil
explain how beta pleated sheets are folded
the polypeptide chain can either turn back on itself or,,, two or more segments of a polypeptide chain lines up next to each other forming a sheet like structure held together by hydrogen bonds that form between carbonyl and amino groups of backbone. the r groups extend above and below the sheet of the polypeptide
what factor determines whether an alpha helix or beta pleated sheet is formed?
the sequence of amino acids of the polypeptide
can proteins have both beta and alpha foldings
yes- most have both
explain what the tertiary structure of polypeptide is
the folding and twisting that results in a final 3d shape of the polypeptide
examples of some bonds that can be found in tertiary structure in proteins
hydrogen bonds, ionic bonds, covalent bonds, disulphide linkages, hydrophobic interactions
what is the quaternary structure of a protein
when diff subunits (many polypeptide chains) come together they give the protein its quaternary structure
give an example of a protein that has a quaternary structure
haemoglobin- made of 4 subunits
what happens to a protein when it is exposed to a change in temperature or pH
the tertiary structure is lost- the protein unravels and is referred to as denatured (non-functional)
can proteins renature
yes- if the denaturation was not too severe + if the condition is removed
