1.6. Proteins Flashcards
Proteins are responsible for…
…every task of cellular life.
monomers of protein
amino acids (a-a)
proteome
all proteins produced by a cell, tissue, or an organism (differ among tissues, basis for cell differentiation)
genome
all DNA of a cell - genome of all cells of the same multicellular organism is the same (originating from the same first cell - zygote)
structure of a-a (+draw)
common group and radical/side/functional group (20 different types- 20 diff. a-a)
…
common group
radical/side/functional group
. same for all a-a, central C atom, amine group, and carboxyl group
- varies between different a-a (gives them their character)
zwitterion model of a-a
more accurate, a-a has both plus and minus charge (overall neutral) because it gains an H in the amine group and loses an H in carboxyl group when in water (ionized in an aq. solution)
amino acids are grouped according to their chemical properties (R group):
- non-polar
- positive charge
- polar
- negative charge
there are more than __ a-a but only __ of them…
20, 20, make proteins of all life
how do a-a speak about common ancestry of all life
all 20 were made before origin of life and the 1st organism used all of them - life still uses the same set of a-a as back then
a-aˇ1+a-aˇ2 =
dipeptide
bond connecting two a-a
peptide bond
oligopeptide
peptide
polypeptide
- 2-20
- 20-40
- 40> (10 000)
approximate number of different proteins that can be made out of a-a is:
20^1000 (generalized: 20^n - n is the number of a-a in a chain)
- but our body makes a lot less (few thousand)
What determines protein function?
structure of proteins (3D shape) which is determined by the sequence of a-a in a protein (chain) which is determined by genes (sequence of nucleotides)
Sequence of a-a is determined by __ and it is…
the gene, crucial for protein function.
explain what causes the specific shape of each polypeptide chain
the sum of all interactions between a-a; some a-a form attraction forces between them, some repel each other so they will stey further apart… (e.g. - charged R group and + charged R group of a-a)
draw the formation of a dipeptide (a-aˇ1=glycine, a-aˇ2=alanine)
…
Some proteins consist of 1 (___) and some of more polypeptide chains (___, ___, ___, ___).
lysozyme (enzyme important for immune system), hemoglobin (Hb)(4), insulin (2), collagen (2), antibody (4)
In water, ___ a-a are outside, sheltering the ___ a-a, and in oil ___ a-a are outside, sheltering ___ a-a.
hydrophilic, hydrophobic, hydrophobic, hydrophilic
name for protein shape (used in biochemistry)
protein conformation
primary protein structure
only speaks about the amino acid sequence and number of a-a in a polypeptide chain (encoded by a specific gene)
secondary protein structure
Formation of patterns within a chain.
H-bonds cause folding of a-a into repeating patterns.
Random coils, alpha helix structures or beta-pleated sheets depending on H-bonds connecting the non-adjacent a-a along a single polypeptide chain.
H-bonds form between (former) carboxyl and amine groups of a-a.
random coil
- no specific relationship between a-a
- determined by temperature, pressure and pH of the environment
- no particular patern
alpha helix
- a-a form helical structures
- stabilized by H-bonds (H and O try to come as close to each other as possible - attraction force) - H-bonds NEVER bond charged a-a only polar
beta-pleated sheets
- represented by a straight arrow in models
- stabilized by H-bonds (attraction force)
tertiary protein structure
Due to interactions between R-groups of non-adjacent a-a, the chain undergoes additional folding.
Final shape is achieved by:
- ionic bonds (+R and - R)
- hydrophobic interactions (hydrophobic a-a in the chain’ interior to avoid contact with H2O)
- H-bonds (polar R groups)
- disulfide bridges (covalent bonds, cysteine a-a: CH2-S)
What are prosthetic groups?
non-protein groups attached to proteins (conjugated proteins)
How are the proteins that have attached prosthetic groups called? Give an example.
conjugated proteins, hemoglobin (Fe)
- the 4 polypeptide chains are not functional without Fe atoms at their core (protected) - O2 will bind to Fe (in red blood cells)
draw a benzene ring
…
quaternary protein shape
the way polypeptide chains fit together when there are more than 1 of them in a protein
Why is protein denaturation (or ___) irreversible?
coagulation; because:
1) increase in temperature - when all atoms absorb the extra E, they will start vibrating, tertiary bonds will be broken and structures will fall apart - meaning that the function of the protein will be lost as well
2) pH too low - H+ concentration too big
- extra H+ ions will intervene with H-bonds and break them - many structures will be broken - loss of all levels of the protein structure - cannot be reformed - works the same when pH is too high (too many OH- ions)
protein denaturation
Some factors (pH, temp.) can alter the conformation of the protein molecule and disrupt its biological function (complete loss of function) by breaking the intermolecular bonds within the chain. E.g. cooking an egg white - cannot go back to transparent from white.
