Unit 1 Flashcards
Phosphorylation Cascades
Involve a series of events with on kinase activating the next and so on.
Phosphorylation cascades can result in the phosphorylation of many proteins.
G-Proteins
Relay signals from activated receptors to target proteins such as enzymes and ion-channels
Process of a peptide/hydrophilic hormone
Reception- Transmembrane receptors change conformation when the ligand binds to the extracellular face; the signal is transduced across the plasma membrane.
Transduction- Transmembrane receptors act as signal transducers by converting the extracellular signals which alters the behaviour of the cell.
Hydrophilic Signalling
Hydrophilic signals molecules bind to transmembrane receptors so do not enter the cytosol.
Process of A Steroid Hormone
Steroid hormone passes across the plasma membrane.
The hormone binds to the receptor protein activates it.
the hormone receptor complex binds to the hormone response elements.
Binding at the HRE influences the rate of transcriptions.
What are the receptors for hydrophobic signalling molecules
Transcription Factors
Transcription Factors
Proteins that when bound to DNA can either stimulate/inhibit initiation of transcription.
Hydrophobic signalling
Hydrophobic signalling molecules can diffuse directly through the phospholipid bi-layer of the membrane, so bind to intracellular receptors.
How are cells ‘Switched on’
Binding changes the conformation of the receptor which initiates a response within the cell.
Receptor Molecules
Proteins with a binding site for specific signal molecules.
Examples of extracellular signalling molecules
Steroid hormones- Vitamin D
Peptide Hormones- Insulin
What drives the active transport of glucose in the small intestine.
The sodium gradient created by the sodium potassium pump drives the active transport of glucose
Sodium Potassium Pump
1- The transporter protein has its ion binding sites exposed to the cytoplasm. The protein has a high affinity for Na+ ions and 3 Na+ ions bind to the sites.
2- When the sodium ions are attached, the transporter protein is able to hydrolyse ATP. The phosphate attaches to the protein to phosphorylate it and this causes a conformational change.
3- This new conformation has its ion binding sites exposed to the outside of the cell, because it has a lower affinity for Na+ ions, they are released outside the cell.
4- This new conformation has a high affinity for K+ ions and 2 K+ ions bind to the proteins outside the cell, this triggers dephosphorylation.
5- Dephosphorylation causes the protein to revert to its original conformation with its binding sites exposed to the cytoplasm.
Step 6- This conformation has a low affinity for K+ ions so the are released into the cell.
How does the sodium potassium pump gain energy and what is its use for it.
Using energy from the hydrolysis of ATP to maintain ion gradients.
Membrane Potential
An electrical potential difference.
What enzymes hydrolyse ATP
ATPases
How does active transport go against the gradient
Using pump proteins that transfer substances across the membrane.
Pump proteins are transporter proteins that are coupled to an energy source.
Transporter Proteins
Bind to specific substance to be transported and undergo a conformational change to transfer the solute across the membrane.
Voltage-Gated Channes
Controlled by changes in ion concentration.
Ligand Gated Channels
Controlled by the binding of signal molecules.
Channels
Multi sub unit proteins with the sub units arranged to form water filled pores that extend across the membrane
Facilitated Diffusion
The passive transport of substances across the membrane through specific transmembrane proteins.
How are peripheral proteins held.
They have hydrophilic R groups on their surface and are bound to the surface membranes, mainly by ionic and hydrogen bond interactions.
What holds integral proteins in the bi-layer.
regions of hydrophobic R groups that allow strong hydrophobic intercations.
What term is used to describe the cell membrane.
Fluid Mosaic Model
What charge does a phosphate group add.
Negative Charge
Phosphotases
Catalyses the removal of a phosphate group.
Kinases
Catalyses the transfer of a phosphate group to other proteins.
What does the addition/removal of a phosphate cause in proteins.
Causes reversible conformational change.
How does pH and temp affect co-operativity of haemoglobin.
Decrease in pH/ increase in temp lowers affinity of haemoglobin for oxygen so binding of 02 is increased.
This means oxygen delivery to tissues is increased.
How is co-operativity shown in haemoglobin
The binding and release of oxygen
Process of modulators
Following binding of a modulator the conformation of the enzyme changes and this alters the affinity of the active site.
What do positive modulators do
Increase enzymes affinity for the substrate
What do negative modulators do
Decrease enzymes affinity for the substrate.
Function of modulators
To regulate the activity of an enzyme when it binds to the allosteric site
What structure do allosteric proteins have
Quaternary structure and consist of multiple sub units.
Denaturation
Increased temp disrupts interactions that hold proteins in shape, protein begins to unfold eventually becoming denatured.
As pH increases or decreases from optimum the ionic interactions between charged groups are lost which changes the conformation of the protein, it becomes denatured.
What happens when a substrate binds to the allosteric site.
It increases the affinity of the other active sites for binding of subsequent substrate molecules.
Ligand binding process
As a ligand binds to the protein binding site the conformation of the protein changes. This change in conformation causes a functional change of the protein.
What do binding sites have to ligands
Complementary shape and chemistry
Ligand
A substance that can bind to a protein.
Quaternary protein structure
Exists in proteins with 2 or more connected polypeptide sub units.
The spatial arrangements of said sub units is the quaternary structure.
Di-Sulfide Bridges
Covalent bonds between R groups containing Sulfur.
Tertiary Protein Structure
The polypeptide folds, this conformation is stabilised by R group interactions:
Hydrophobic interactions, ionic bonds, LDF’s, hydrogen bonds and disulfide bridges.
Secondary Protein Structure
Hydrogen bonding along the backbone of the protein strand results in regions of secondary structure;
Alpha Helices, Parallel or anti-parallel beta plated sheets, turns.
Primary Protein Structure
Sequence in which the amino acids are synthesised onto the polypeptide.
What are the three different types of R groups.
Basic (positive charge)
Acidic (negative charge)
Polar (hydrophobic)
How do R groups differ
Shape, charge, hydrogen, bonding capacity and chemical reactivity.
Examples of secreted proteins
Digestive Enzymes
Peptide Hormones
How do proteins become active after secretion
Through proteolytic cleavage, breaking peptide bonds between the amino acids in the protein.
Secretory Pathway
1- proteins that have to be secreted are translated in the ribosomes on the RER. They enter the lumen.
2- The proteins move through the Golgi Apparatus as normal and are packaged into vesicles.
3- The vesicles move to the membrane and fuse with it, releasing their contents into the cell
What are the major modifications of the proteins
The addition of complex carbohydrates, cutting/combining of strands, addition of phosphate groups.
Movement of proteins between membranes
Once the proteins are in the ER, they are transported by vesicles that bud off from the endoplasmic reticulum and fuse with the Golgi apparatus. As proteins move through the G.A they undergo post translational modifications. Vesicles move along microtubules to other membranes and fuse with them within a cell.
Synthesis of transmembrane proteins
The synthesis of all transmembrane proteins begins at the cytosolic ribosomes;
- A polypeptide that will become part of a transmembrane protein starts with a short strand of about 20 amino acids called a signal sequence. When the signal sequence emerges from the ribosome a cytosolic particle binds to it and halts translation.
2.The particle also directs the ribosome to dock with a protein pore on the endoplasmic reticulum thus forming Rough ER.
- After docking, the protein pore removes the cytosolic particle and the signal sequence so translation can continue.
- As it is translated the polypeptide chain is inserted directly into the membrane of the ER. The ribosome is released back into the cytosol once translation finishes.
Vesicles
Vesicles are fluid filled sacs which transport materials between different membrane components.
Lysosomes
Membrane bound organelles containing a variety of hydrolases that digest proteins, lipids, nucleic acid and carbohydrates.
Golgi Appartus
A series of flattened membrane discs.
Its job is to process proteins to be used inside and outside the cell.
Endoplasmic Reticulum
The ER forms a network of membrane tubules that branch off from the nuclear membrane.
It folds proteins and transports completed proteins to the Golgi apparatus.
Why can some vital functions not be carried out by them membrane in eukaryotes.
Because the plasma membrane is too small.
