2.4 Proteins Flashcards
what are proteins compromised of?
long chains of recurring monomers (amino acids)
what are the basic structures of a central carbon atom? (4)
- an amine group (NH2)
- a carboxylic acid group (COOH)
- hydrogen atom (H)
- a variable side chain (R)
how many different amino acids are universal to all organisms?
around 20
how are amino acids joined together?
amino acids are joined together on the ribosome to form long chains (polypeptide), which make up proteins
how does each type of amino acid differ?(2)
- differ in the composition of the variable side chain
- with distinct chemical properties and cause the protein to fold and function differently according to its specific position within the polypeptide chain
how are amino acids joined together?
joined together by a covalent bond (peptide bond) in a condensation reaction to form a dipeptide and water
what are long chains of covalently bonded amino acids called?
polypeptides
how can polypeptide chains be called?
can be broken down via hydrolysis reaction (required water to reverse the process)
where are peptide bonds formed? (2)
between the amine and carboxylic acid groups of adjacent amino acids
- the amine group loses a hydrogen atom (H) and the carboxylic acid loses a hydroxyl (OH) - this forms water (H2O)
what is the order of the amino acid sequence called? (3)
primary structure
- determines the way the chain will fold
- different amino acid sequences will fold into different configurations due to the chemical properties of the variable side chain
what will amino acid sequences commonly fold into? (3)
secondary structures
- alpha helices -> when amino acid sequence folds into a coil/spiral arrangement
- beta-pleated sheets -> when the amino acid sequence adopts a directionally orientated staggered strand configuration
how are alpha-helices and beta-pleated sheets formed?(2)
from hydrogen bonds fomring between non-adjacent amine and carboxyl groups
(when no secondary structure exists, the polypeptide chains will form a random coil)
what is the overall 3D configuration of the protein called?
tertiary structure
how are tertiary structures determined? (2)
- tertiary structure of a polypeptide chain will be determined by the interactions between the variable side chain
- these interactions may include hydrogen bonds, disulphide bridges, ionic interactions, polar associations
what can change the overall shape of the polypeptide chain and are determined by the position of specific amino acids within a sequence?
the affinity/repulsion of the side chains
(so, the order of the amino acid sequence (primary structures) determines all subsequent levels of protein folding)
what is the fourth level of structural organisation called?
quaternary structure
what are quaternary structures made of?
proteins that consist of more than one polypeptide chain linked together
what is an example of a protein with a quaternary structure? (3)
haemoglobin
- haemoglobin is composed of 4 polypeptide chains (2 a and 2 b)
- it is composed of iron-containing haeme groups (prosthetic groups responsible for binding oxygen)
what is denaturation?
structural change in a protein that results in the loss (usually permanent) of its biological properties
(because the way a protein fold determines its function, any change or abrogation of the tertiary structure will alter its activity)
what two things usually cause the denaturation of proteins?
- temperature
- pH
how does temperature denature a protein?(3)
- high levels of thermal energy may disrupt the H-bonds that hold the protein together
- as these bonds are broken, the protein will begin to unfold and lose its capacity to function as intended
- temperature at which proteins denature may vary, but most human proteins function optimally at body temperature
how does pH denature a protein? (3)
- amino acids are zwitterions, neutral molecules possessing both negatively (COO-) and positively (NH3+) charged regions
- changing the pH will alter the charge of the protein solubility and overall shape
- all proteins have optimal pH which is dependent on the environment in which it functions
what is a gene?
gene is a sequence of DNA which encodes a polypeptide sequences
what process is a gene sequence converted into a polypeptide sequence? (2)
- transcription - making mRNA transcript based on a DNA template (occurs in the nucleus)
- translation - using the instructions of the mRNA transcript to link amino acids together (occurs at the ribosome)
usually, one gene will code for one polypeptide, but what exceptions to this rule? (3)
- genes may be alternatively spliced to generate multiple polypeptide variants
- genes encoding tRNA sequences are transcribed but never translated
- genes may be mutated (their base sequence is changed) and consequently produce an alternative polypeptide sequence
what is the proteome?
the totality of proteins expressed within a cell. tissue or organism at a certain time
why will any given individual proteome be unique?
as protein expression patterns are determined by an individual’s genes
what are the factors which cause the proteome to be significantly larger than the number of genes in an individual?
- gene sequences may be alternatively spliced following transcription to generate multiple protein variants from a single gene
- proteins may be modified (eg. glycosylated, phosphorylated) following translation to promote further variations
what are 7 roles of a proteins?
structure - collagen, spider silk
hormones - insulin, gucagon
immunity - immunoglobins
transport - haemoglobin, cytochrome
sensation - rhodopsin
movement - actin, myosin
enzymes - rubisco
