2.4 proteins Flashcards
what are proteins?
- polymers made from amino acids which are
the monomers - 20 amino acids that make up proteins found in cells
- properties of proteins are determined by R group on the amino acids
- structure:
NH2 (amino group) CHR COOH (carboxyl group)
how are amino acids linked to form polypeptides?
- by condensation reaction
- OH in carboxyl group of 1 combines with H in amino group of another
- bond combining the 2 amino acids is peptide bond
what are the 2 ends of a polypeptide called?
amino end: N-terminus
carboxyl end: C-terminus
why are there infinite possibilities of polypeptides?
- could be any length
- 20 amino acids
- amino acids in any sequence, order or combination
where are polypeptides produced?
- at the ribosomes in cells
- amino acids linked together in specific sequence as dictated by genes
what are genes?
- sequences of DNA nucleotides carrying information for expression
how does dna become polypeptides?
dna -> (transcription) rna -> (translation) polypeptide
- dna strand is transcribed
what is the start codon?
AUG
what is the stop codon?
UAG
what are the 4 levels of protein structure that determine the final shape of the protein?
- primary
- secondary
- tertiary
- quaternary
what is the primary protein structure?
- sequence of amino acids along the polypeptide chain
- determined from the genetic information stored in the cell
what is the secondary protein structure?
- parts of the polypeptide chain can coil onto itself, leading to the formation of alpha helices
- other parts of the polypeptide chain can fold itself in a beta pleated structure
- hydrogen bonds between amino acid molecules stabilise these secondary structures
what is the tertiary protein structure?
- overall three dimensional shape of a protein
- usually arises from the interactions and bonds formed
between R groups of amino acids within the protein - e.g disulphide bridge formed between two sulphur containing amino acids, leading to a strong bond formed
what is the quaternary protein structure?
- when two or more polypeptide chains associate to form a resultant protein, this level of structure is the quaternary structure
- not all proteins have a quaternary structure
- collagen, which exists in a triple helix, is an example of a protein with a quaternary structure
can a protein consist of a single polypeptide? or must it always be more than 1 polypeptide linked together?
yes it can. multiple can be seen in quaternary structure but there are also proteins made of 1 single polypeptide.
what are the different functions of proteins?
- enzymatic proteins
- storage proteins (e.g. casein in milk as a storage for amino acids; egg albumin as a storage for amino acids)
- hormonal proteins (insulin, glucagon, adrenaline, etc)
- contractile and motor proteins (actin and myosin found in muscle cells)
- defensive proteins (antibodies clumping onto bacteria)
- transport proteins
- receptor proteins
- structural proteins
or SHITS ME
- structure – e.g. collagen, spider silk
- hormones – e.g. insulin, glucagon
- immunity (defensive) – e.g. immunoglobulins
- transport – e.g. haemoglobin
- sensation (receptor)– e.g. rhodopsin
- movement – e.g. actin, myosin
- enzymes – e.g. Rubisco, catalase
how do enzymatic proteins function?
- enzyme available w empty active site
- substrate binds to enzyme w induced fit
- substrate is converted to products
- products are released
what is genome?
refers to the sum of all genes encoded within the DNA of that species
what is proteome? and is it unique?
- proteome refers to the sum of all proteins that can be produced by the species
- dependent on the genome of the species, as well as the environment that affects which genes are expressed at that point in time
- genome is unique for each species, likewise the proteome is also unique for each species
what is rubisco?
- ribulose bisphosphate carboxylase
- enzyme used to fixed carbon dioxide from the atmosphere
- provides a source of carbon during photosynthesis and formation of complex carbon compounds
- found in high concentration in leaves of plants
what is insulin?
- hormone used to regulate blood glucose levels
- secreted in response to high blood glucose levels, to stimulate cells to take in glucose
- produced by the pancreas
what are immunoglobulins?
- also known as antibodies
- total of 2 antigen binding sites per protein
- rest of antibody is fixed, but different antibodies will have different antigen binding sites, leading to great specificity
- can agglutinate bacteria, as antibodies can bind to antigens, and also bind to each other
- agglutinated bacteria are not able to cause infections, and being clumped together makes the bacteria easier to be engulfed by white blood cells via phagocytosis
what is rhodopsin?
- pigment that can absorb light
- also known as visual purple
- found in receptor cells in the retina
- when a photon reaches a rhodopsin molecule, isomerisation occurs leading to a change in shape of the molecule
• sets off a chain of events that leads to the depolarisation of receptor cells and subsequently nerve cells
what is collagen?
- triple helix
- structural protein, and about a quarter of all proteins
found in the human body is collagen - forms a mesh in tissues, allowing for resistance against tearing and shearing
- gives structural strength to tendons, ligaments, skin and blood vessels
what is spider silk?
- used to form webs by spiders
- stronger than steel cables or Kevlar fibres if they all are of equivalent thickness
- when stretched the fibres can extend, giving a greater resistance against breaking
why do proteins denature at high heat or deviation of pH from optimum?
- three dimensional shape of a protein is maintained by numerous internal bonds between amino acids in the protein
- most of these bonds are relatively weak, and can be easily broken at higher temperatures
- heat energy can increase the rate of vibration of atoms, and this vibration can break the weak internal bonds
- extreme pH can change the charges of R groups on amino acids, breaking ionic bonds and hence leading changes in shape of the protein
