Cells and Proteins Flashcards
What is the proteome?
The entire set of proteins that is, or can be, expressed by a genome, cell tissue, or organism at a certain time
Why is the proteome greater than the number of genes?
Because more than one protein can be produced from a single gene as a result of alternative RNA splicing.
Are all genes expressed as proteins?
No, genes that do not code for proteins are called non-coding RNA genes.
How can protein expression in a given cell type vary?
Protein expression can vary over time and under different conditions e.g. metabolic activity of the cell, cellular stress, the response to signalling molecules, diseased versus healthy cells.
What do eukaryotic cells have that increases the total area of the membrane?
Eukaryotic cells have a system of internal membranes which increases the total area of the membrane.
What does the endoplasmic reticulum form?
The ER forms a network of membrane tubules continuous with the nuclear membrane.
What is the golgi apparatus?
The golgi apparatus is a series of flattened membrane discs.
What are lysosomes?
Lysosomes are membrane-bound organelles containing a variety of hydrolases that digest proteins, lipids, nucleic acids and carbohydrates.
What do vesicles do?
Vesicles transport materials between membrane compartments.
Where are lipids and proteins synthesised?
Lipids and proteins are synthesised in the endoplasmic reticulium.
Where exactly are lipids synthesised?
Lipids are synthesised in the smooth endoplasmic reticulum and inserted into its membrane.
Where does the synthesis of all proteins begin?
The synthesis of proteins begins in the cytosolic ribosomes.
What happens after cytosolic proteins have been synthesised in the cytosolic ribosomes?
the cytosolic proteins remain in the cytosol.
What happens to transmembrane proteins after synthesis in the cytosolic ribosomes?
Transmembrane proteins carry a signal sequence, which halts translation and directs the ribosome synthesising the protein to dock with the ER, forming RER.
What happens after docking at the ER?
Translation continues and the protein is inserted into the membrane of the ER.
What happens after the protein has been inserted into the ER?
The protein is transported by vesicles that bud off from the ER and fuse with the golgi apparatus.
What happens at the golgi apparatus?
The proteins move through the golgi apparatus and undergo post-translational modifications.
What is the major modification that happens in the golgi apparatus?
The addition of a carbohydrate group.
What happens after modifications at the golgi apparatus?
Vesicles that leave the golgi apparatus take proteins to the plasma membrane and lysosomes.
What happens to the vesicles after proteins have been taken to the plasma membrane or lysosomes?
Vesicles move along microtubules to other membranes and fuse with them within the cell.
What happens to secreted proteins after synthesis in the cytosolic ribosomes?
They have a signal sequence which halts translation and docks at the ER. Translation continues in ribosomes on the RER and it enters its lumen.
What happens after the secreted proteins enter the lumen?
The proteins move through the golgi apparatus and are then packaged into secretory vesicles.
What happens after secreted proteins are out into secretory vesicles?
The vesicles move to and fuse with the plasma membrane, releasing the proteins out of the cell.
Why do many secreted proteins require proteolytic cleavage?
Many secreted proteins are synthesised as inactive precursors and require proteolytic cleavage to produce active proteins.
What are proteins?
Proteins are polymers of amino acid monomers.
What are amino acids linked by?
Amino acids are linked by peptide bonds to form polypeptides.(CONH)
Explain amino acids basic structure.
Amino acids have the same basic structure differing only in R group.
How are amino classified?
Amino acids are classified according to their R group: basic (positively charged), acidic (negatively charged), polar and hydrophobic
What causes the diversity of amino acid R groups?
The wide range of functions carried out by proteins.
What is the primary structure?
The sequence in which the amino acids are synthesised into the polypeptide.
What causes secondary structure regions?
Hydrogen bonding along the backbone of the protein strand.
What are secondary structures?
Alpha helix, parallel or anti-parallel beta-pleated sheets or turns.
How is a tertiary structure made?
The polypeptide folds into a tertiary structure.
What stabilises the conformation if the tertiary structure?
Interactions between R groups such as: Hydrophobic interactions, ionic bonds, London dispersion forces, hydrogen bonds and disulfide bridges
Where does a quaternary structure exist?
In proteins with two or more connected polypeptide subunits.
What is a prosthetic group?
A prosthetic group is a non-protein unit tightly bound to a protein and necessary for its function.
How can interactions between R groups be influenced?
Temperature and pH
How does temperature influence R group interactions?
Increasing temperature disrupts the interactions that hold the protein in shape. The protein being to unfold, eventually becoming denatured.
How does pH influence R group interactions?
The charges on acidic and basic R groups are affected by pH. As pH increases or decreases from the optimum, the normal ionic interactions between charged groups are lost, which gradually changes the conformation of the protein until it becomes denatured.
What is a ligand?
A ligand is a substance that can bind to a protein.
What can allow binding to ligands?
R groups not involved in protein folding can allow binding to ligands.
What do the binding sites have to bind to a ligand?
The binding site will have complementary shape and chemistry to the ligand.
What happens when a ligand binds to a protein-binding site?
The conformation of the protein changes.
What happens when the conformation of a protein changes?
Causes the protein to have a functional change in the protein.
Where do allosteric interactions happen?
Occur between spatially distinct sites.
Do allosteric proteins have subunits?
Many allosteric proteins consist of multiple subunits.
What does allosteric proteins with multiple subunits show?
Allosteric proteins with multiple subunits show cooperativity in binding, meaning that changes in binding at one subunit alter the affinity of the remaining subunits.
What do allosteric enzymes contain?
Allosteric enzymes contain a second type of site, called an allosteric site.
What do modulators do?
Modulators regulate the activity of the enzyme when they bind to the allosteric site.
What happens after a modulator has binded?
The conformation of the enzyme changes and this alters the affinity of the active site for the substrate
What does the binding of oxygen in haemoglobin show?
Cooperativity
What lowers the affinity of haemoglobin for oxygen?
A decrease in pH or an increase in temperature lowers the affinity of haemoglobin for oxygen, so the binding of oxygen is reduced.
Why is reduced pH and an increase in temperature goof (haemoglobin and oxygen)?
Reduced pH and increasing the temperature in actively respiring tissue will reduce the binding of oxygen to haemoglobin promoting increased oxygen delivery to tissue.
What can cause reversible conformational changes in proteins?
The addition or removal of phosphate can cause reversible conformational changes in proteins.
What is a common post-translational modification?
Addition or removal of a phosphate.
What do protein kinases do?
Catalyse the transfer of a phosphate group to other proteins.
What phosphate is transferred to specific R groups in a protein.
The terminal phosphate of ARP.
What catalyses the reverse reaction? (Removing a phosphate)
Protein phosphatatses
What happens during phosphorylation?
Brings about a conformational changes, which can affect a protein’s activity. The activity of many cellular proteins is regulated in this way.
How does phosphorylation affect a protein?
Some proteins are activated while others are inhibited.
