Unit 1 - Proteins Flashcards
What is the proteome?
The entire set of proteins expressed by a genome.
How can the proteome be larger than the number of genes?
More than one protein can be produced from
a single gene as a result of alternative RNA
splicing.
What are genes that do not code for proteins called?
Non-coding RNA genes.
What do genes that do not code for proteins do?
They are transcribed to produce tRNA,
rRNA, and RNA molecules that control the
expression of other genes.
Giver 4 examples of factors affecting the set of proteins expressed by a given cell type.
Metabolic activity of the cell, cellular stress,
the response to signalling molecules, and
diseased versus healthy cells.
What do eukaryotic cells have that increases the total area of their membrane?
System of internal membranes.
Why can’t the plasma membrane of eukaryotic cells carry out all the vital functions of membranes?
Because of their size, eukaryotes have quite a small surface area to volume ratio so the plasma membrane is too small to carry out all of the vital functions of membranes.
What is the endoplasmic reticulum?
Network of membrane tubules connected to the nuclear membrane.
What is the golgi apparatus?
A series of flattened membrane discs.
What are lysosomes?
Membrane-bound organelles containing a variety of hydrolases that digest proteins, lipids, nucleic acids and carbohydrates.
What do vesicles do?
Transport materials between membrane compartments.
What is the difference between the rough endoplasmic reticulum and the smooth endoplasmic reticulum?
Rough ER (RER) has ribosomes on its cytosolic face while smooth ER (SER) does not.
Where are lipids synthesised?
Synthesised in the smooth endoplasmic reticulum and inserted into its membrane.
Where does the synthesis of all proteins begin?
Cytosolic ribosomes.
Where is the synthesis of cytosolic proteins completed and where do these proteins end up?
Synthesis is completed in cytosolic ribosomes and proteins remain in the cytosol.
Give two examples of secreted proteins.
Peptide hormones and digestive enzymes.
What is the first step in the secretory pathway?
Secreted proteins are translated in ribosomes
on the RER and enter its lumen.
What happens in the secretory pathway after the secreted protein enters the lumen of the RER?
The proteins move through the Golgi apparatus and are then packaged into secretory vesicles. These vesicles move to and fuse with the plasma membrane, releasing the proteins out of the cell.
What happens if a secreted protein is synthesised as an inactive precursor?
Undergoes proteolytic cleavage to produce an active protein.
Give one example of a secreted protein that requires proteolytic cleavage to become active.
Digestive enzymes
What type of bond are amino acids linked by?
Peptide bond.
Draw a peptide bond.
O H
|| |
- C – N -
Draw the basic structure of an amino acid.
H R O
\ | //
N - C - C
/ | \
H H OHWhat are the 4 classes of R group?
Basic (positively charged)
Acidic (negatively charged)
Polar
Hydrophobic
What does the wide range of functions carried out by proteins result from?
The diversity of amino acid R groups.
What is the primary structure?
The sequence in which the amino acids are synthesised into the polypeptide.
What causes the formation of the secondary structure?
Hydrogen bonding along the backbone of the protein strand.
What are the three types of secondary structure?
Alpha helixes
Parallel or antiparallel beta-pleated sheets
Turns
How is the tertiary structure formed?
The polypeptide folds into the tertiary structure.
What is the tertiary structure stabilised by? Give examples.
Interactions between R groups such as hydrophobic interactions, ionic bonds, London dispersion forces, hydrogen bonds, disulfide bridges
In what type of protein does the quaternary structure exist?
Proteins with two or more connected polypeptide subunits.
What is the name given to a non-protein unit tightly
bound to a protein and necessary for its
function?
Prosthetic group.
Give an example of a protein with a prosthetic group.
Haemoglobin - its ability to bind to oxygen is dependent on the prosthetic group, haem.
What can interactions of R groups be influenced by?
Temperature and pH.
How does increasing temperature affect a protein?
Increasing temperature disrupts the interactions that hold the protein in shape. The protein begins to unfold and eventually becomes denatured.
What are the charges on acidic and basic R groups affected by?
pH.
How does pH affect charges on acidic and basic R groups?
As pH increases or decreases from the optimum, the normal ionic interactions between R groups are lost, which gradually changes the conformation of the protein until it becomes denatured.
What is a ligand?
A substance that can bind to a protein.
What happens to the conformation of a protein as a ligand binds to it and what does this result in?
Conformation changes which causes a functional change in the protein.
What is the structure of many allosteric proteins?
Quaternary.
What happens when a substrate molecule binds to one active site of an allosteric enzyme and what is the importance of this?
Increases the affinity of the other active sites for binding of more substrate molecules. This is important because the activity of allosteric enzymes can vary greatly with small changes in substrate concentration.
What binding feature do allosteric proteins with multiple subunits show?
Co-operativity.
What regulates the activity of an enzyme that binds to allosteric sites?
Modulators.
What happens following binding of a modulator to an allosteric enzyme?
The conformation changes which alters the affinity of the active site for the substrate. This can be positive or negative.
Give an example of an enzyme which shows co-operativity.
The binding and release of oxygen in haemoglobin.
What two things lower the affinity of haemoglobin for oxygen?
Decrease in pH
Increase in temperature
What is the importance of reducing binding of oxygen to haemoglobin?
Promotes increased oxygen delivery to tissue.
What enzymes catalyse the addition of a phosphate group?
Kinases.
What is the phosphate that is transferred to specific R groups on a protein?
The terminal phosphate of ATP.
What enzymes catalyse the removal of a phosphate group from a protein?
Protein phosphatases.
What does phosphorylation result in?
Conformational changes which can affect a protein’s activity.
What type of charge does addition of a phosphate add?
Negative charges.
What is the significance of the reversible nature of phosphorylation?
Allows activity of many cellular proteins such as enzymes and receptors to be regulated.
