Flashcards in MGD 1- Proteins Deck (108)
In what part of the cell does rRNA synthesis occur?
Nucleus / nucleolus
Why do mitochondria contain 'cristae'?
To maximise the surface area of the inner mitochondrial membrane, for maximum ATP synthesis.
What are ribosomes made up of?
Proteins and rRNA molecules
What type of ribosomes do bacteria and archaea have?
70S = 30S + 50S
What type of ribosomes do eukaryotes have?
80S = 40S + 60S
Which organelle performs glycosylation of proteins and lipids?
Which Golgi cisternae faces the rER?
Which Golgi cisternae faces the plasma membrane?
Why is glucose a 'polar', soluble molecule?
Contains -OH (hydroxyl) groups which can form bonds with water molecules
Why is palmitate a 'non-polar', insoluble molecule?
Does not contain any -OH (hydroxyl) groups, so cannot interact with water molecules
Which molecules are more soluble: polar or non-polar? Why?
Polar, as they contain -OH (hydroxyl) groups which can interact with water molecules
What is an amphipathic molecule?
A molecule with both polar and non-polar regions
Which protein isomer is found naturally?
Is a strongly acidic protein is likely to have a high pK or low pK value?
What is physiological pH?
What is the 'Isoelectric point' of a protein?
The pH at which there is no net charge on the protein.
Do acidic or basic amino acids become positively charged?
Basic amino acids become positively charged
Do acidic or basic amino acids become negatively charged?
Acidic amino acids become negatively charged
Which protein terminal is synthesised first?
What are the 2 secondary structures of a protein?
1- alpha helix
2- beta sheet
How many amino acids are required for 1 turn of an alpha helix?
What is the height (nm) of 1 turn of an alpha helix?
Which 2 amino acids are 'alpha helix breakers'?
Proline and Glycine
What is the distance (nm) between amino acid residues in a beta-sheet?
What are the 4 main ways to denature a protein?
4- Reducing agent
How does heat often denature proteins?
Heat increases the kinetic energy of the molecules, breaking weak hydrogen and ionic bonds, unfolding the protein.
How does a change in pH often denature proteins?
This will alter the ionisation states of the amino acids, breaking ionic and hydrogen bonds, unfolding the protein
How do detergents denature proteins?
They disrupt the hydrophobic interactions within a protein
Give an example of a reducing agent:
How do reducing agents denature proteins?
They break covalent disulphide bonds
What is a 'transmissable spongiform encephalopathy'?
A prion disease which affects the brain and nervous system
Give 3 examples of transmissable spongiform encephalopathies:
1- Bovine spongiform encephalopathy (BSE)
2- Creutzfeld-Jakob Disease (CJD)
Define amyloid fibrils:
Misfolded insoluble form of a normally soluble protein, which aggregates and is resistant to degradation.
What type of protein assists the folding of other proteins?
What is the small conformational change caused when oxygen binds to haem in haemoglobin?
The Fe atom is pulled into the plane of the porphyrin ring
How many haem groups are in haemoglobin?
How many haem groups are in myoglobin?
What is the function of myoglobin?
To store O2 in muscle
What is the shape of a Myoglobin O2-binding curve?
What is the shape of a Haemoglobin O2-binding curve?
Why does Haemoglobin have a sigmoidal O2-binding curve?
As it exhibits co-operative binding of O2 (Must change from low-affinty T state, to high-affinity R state)
What is the T state of Haemoglobin?
The tense state of Haemoglobin is deoxyhaemoglobin, when it has low affinity for oxygen.
What is the R state of Haemoglobin?
The relaxed state of Haemoglobin is oxyhaemoglobin, when it has high affinity for oxygen.
Name 3 molecules which affect O2 binding to Haemoglobin:
What is the full name of 2,3-BPG?
Why does 2,3-BPG promote O2 release from Haemoglobin?
2,3-BPG binds to Haemoglobin where O2 usually binds
Why does the amount of 2,3-BPG present increase at higher altitudes?
To promote O2 release at tissues, as ppO2 drops exponentially with increased altitude.
How does adult haemoglobin differ from foetal haemoglobin, in BPG binding?
Foetal haemoglobin binds 2,3-BPG much less tightly than adult haemoglobin, allowing O2 to be readily passed from adult maternal Hb to foetal Hb.
What is meant by the Bohr effect?
An increase of H+ / CO2 causes a decrease in pH, which lowers the affinity of Hb for O2, promoting deoxyhaemoglobin.
How does the Bohr effect alter the Haemoglobin O2-binding curve?
It causes it to shift to the right
How does an increase in pH alter the Haemoglobin O2-binding curve?
It causes it to shift to the left
How does an increase in temperature alter the Haemoglobin O2-binding curve?
It causes it to shift to the right
How does a decreased pH alter the Haemoglobin O2-binding curve?
It causes it to shift to the right
How is the Bohr effect related to metabolically active tissues?
Metabolically active tissues produce more CO2, which causes an increased [H+] in the area, which produces the Bohr effect, promoting the dissociation of O2 from haemoglobin.
At what point is CO poisoning usually fatal?
When COHb > 50%
Why is CO poisoning often fatal?
CO binds to Hb much more readily than O2, so prevents O2 transport.
What and where does the mutation occur which causes Sickle Cell Anaemia?
A>T, Glu6>Val in beta Hb chain
What happens to HbS when in deoxygenated T state?
Forms hydrophobic interactions with adjacent chains, creating sticky hydrophobic pockets. These polymerise, distorting the RBC into a 'sickle' shape.
Why is anaemia a common symptom of Sickle cell disease?
The constant sickling and un-sickling of RBCs reduce their life-span, increasing haemolysis, reducing the number of RBC's in circulation
What is the inheritance pattern of Sickle Cell Anaemia?
Why hasn't Sickle Cell Anaemia been eradicated by natural selection?
Provides resistance against Malaria.
Why is the amino acid change caused by Sickle cell disease so important?
The amino acid change from Glu to Val changes the polarity of the protein, as Glu is negatively charged, whereas Val is non-polar.
What is alpha thalassaemia?
Decreased or absent alpha globin chain production
How many genes are involved in the production of the alpha haemoglobin chain?
How many genes are involved in the production of the beta haemoglobin chain?
How many genes must be affected to cause chronic anaemia due to alpha thalassaemia?
How many genes must be affected in alpha thalassaemia to cause a miscarriage/stillbirth?
Why does alpha thalassaemia cause miscarriage, but beta thalassaemia does not?
Foetus' require alpha chains to form their haemoglobin, they do not require beta chains until after birth.
If only 1 alpha globin gene is affected in alpha thalassaemia, what are the symptoms?
No / little effect, as 3 normal genes
If both genes are affected by beta thalassaemia, what treatment is required?
Lifelong blood transfusions.
At what age does beta thalassaemia present?
~ 6 months after birth
Which chains make up foetal haemoglobin?
alpha and gamma chains
Sickle cell disease reduces the life span of a RBC from 120 days to what?
What are the 3 main ways to increase the rate of a reaction?
1- Increase amount of enzyme present
2- Increase the concentration of reactants present
3- Increase the temperature
When plotting Rate vs [Substrate], what kind of curve do MOST enzymes give?
What is Km?
The substrate concentration at half the maximum rate of reaction.
What is Vmax?
The maximum rate of reaction, when all enzyme active sites are saturated with substrate.
Describe the affinity of an enzyme for its substrate if it has a high Km:
Low affinity - requires a higher substrate concentration to reach Vmax
Describe the affinity of an enzyme for its substrate if it has a low Km:
High affinity - requires ow substrate concentration to reach Vmax.
Name the 2 enzymes which can phosphorylate Glucose into Glucose 6-phosphate:
Which enzyme is necessary for the 1st step in glycolysis, present in most tissues in the body?
Which enzyme is necessary for the 1st step of glycolysis to occur in the Liver?
Which has higher affinity for glucose: Hexokinase or Glucokinase?
What initiates the activity of Glucokinase (in the Liver)?
Feeding, causing an increase in blood glucose levels.
What kind of curve is produced by the Lineweaver-Burk plot?
What value is given at the point where a Lineweaver-Burk plot crosses the x-axis?
What value is given at the point where a Lineweaver-Burk plot crosses the y-axis?
What are the 2 types of reversible enzyme inhibitors?
How does a competitive inhibitor affect the Km and Vmax of an enzyme?
How does a non-competitive inhibitor affect the Km and Vmax of an enzyme?
What are the 4 short-term ways to regulate an enzymes activity?
1- Change substrate/product concentration
2- Allosteric regulation
3- Covalent modification
4- Proteolytic activation
What is allosteric regulation?
The binding of an activator/inhibitor not at the active site, to stabilise either the T or the R state, affecting the enzymes conformation. They exhibit positive co-operativity, as multiple subunits can be allosterically regulated, producing a sigmoidal curve.
Phosphofructokinase can be allosterically regulated. Name an activator and an inhibitor found in the human body:
Activator: AMP, F-2,6-B
Inhibitor: ATP, Citrate, H+
Does phosphorylation activate or inhibit glycogen breakdown?
What is a kinase?
An enzyme which adds a phosphate group
What is a phosphatase?
An enzyme which removes a phosphate group
Inactive enzyme precursor
What are the 2 long-term ways to regulate an enzymes activity?
1- Change rate of protein production
2- Change rate of protein degradation
What is meant by 'enzyme cascade'?
Succession of activation reactions following an initial stimulus
Damage to endothelial blood vessel walls causes them to release...?
- Factor III
What is the role of endothelins in the clotting cascade?
Stimulate vasoconstriction and cell division
What is the role of Factor III in the clotting cascade?
Involved in the production of Thrombin from Prothrombin
What is the role of Thrombin in the clotting cascade?
- Cleave Fibrinogen into Fibrin
- Activate co-factors
Why is Ca2+ necessary for clot formation?
- Required to allow Factor with Gla domains to interact with damaged site
- Attracts -vely charged clotting factors out of the blood
What 3 processes cause termination of clotting?
1- Digestion of clotting factors by proteases
2- Dilution of clotting factors y blood flow and removal by Liver
3- Specific inhibitors
What is required to breakdown the fibrin clot?
What is the zymogen of Plasmin?