Lectures 16-20 Flashcards
Look at protein ligand binding kinetics
Slide 2, lecture 16
What is a sigmoidal curve? (Look at slide 4, lecture 16 for diagram)
A composite of the curves that would be obtained if the sub-units were either only in low affinity form or only in high affinity form
Look at co-operativity graph
Slide 5, lecture 16
Look at slide 8, lecture 16
Effect of positive effectors on sigmoidal curve
Examples of oxygen carrying proteins
Myoglobin
Haemoglobin
What do oxygen carrying proteins contain?
The protein globin and the haem grouping
What is responsible for binding to oxygen in oxygen carrying proteins
The Fe2+ in the centre of the haem group
What state must the Fe be in in order for effective binding to oxygen to occur, in oxygen carrying proteins
The ferrous (II) oxidation state
Where does myoglobin store oxygen?
In the muscle
Where does haemoglobin transport oxygen?
From the lungs to the tissue
Different functions of oxygen carrying proteins depends on what?
Their different structures
What is the structure of myoglobin?
It is a single molecule
What is the structure of haemoglobin?
4 sub-units
Is the myoglobin curve sigmoidal?
No
Look up what a sigmoidal curve looks like
Online
Look at slide 10, lecture 16
Myoglobin curve
Haemoglobin is made up of how many sub-units?
Four
Describe the make-up of haemoglobins sub-units
2 alpha sub-units
2 beta sub-units
Each sub-unit has a haem group bound to it
One molecule of haemoglobin can bind how many molecules of oxygen?
Four
Is haemoglobin and allosteric protein?
Yes
Haemoglobin is an allosteric protein, what does this show?
Co-operativity of binding for oxygen
What shape is the binding curve for haemoglobin and oxygen?
Sigmoidal in shape
Slide 13, lecture 16, also look in PE book at BOHR shift
Haemoglobin oxygen curve
BPG acts as what kind of an effector for Hb?
BPG acts as a negative effector
What is the effect of BPG?
The effect of BPG is that more O2 is delivered to the tissues
How does BPG work?
It decreases Hb’s affinity for oxygen so when the oxygen gets to the muscle it is released more easily and so the muscles get a sufficient supply of oxygen
Slide 16, lecture 16
Haemoglobin +/- BPG curve
What is the allosteric effector for haemoglobin
BPG
How many sub-units is foetal haemoglobin made up of?
Four
What is the make up of foetal haemoglobin’s 4 sub-units?
2 - Alpha
2 - Gamma
Pure adult haemoglobin binds to O2 more efficiently in a test tube than in the blood, why?
The presence of BPG
Does foetal haemoglobin bind more strongly to oxygen that adult haemoglobin?
Yes
Why does foetal haemoglobin bind more strongly to oxygen that adult haemoglobin?
It has a lower affinity for BPG
In the placenta, does both maternal and foetal tissue have the same partial pressure of oxygen?
Yes
In the placenta, why must foetal haemoglobin be able to bind more tightly to O2 than adult haemoglobin?
This is because maternal and foetal tissue in the placenta has the same pO2
Therefore, foetal Hb must be able to bind more tightly so that O2 is transferred from maternal blood to foetal blood
Slide 19, lecture 16
HbF and HbA
Foetal Hb is very efficient for O2 uptake where?
Across the placenta
Foetal Hb is not as efficient as adult Hb in transferring O2 from where to where?
From lungs to tissues
Until all foetal Hb in neonatal blood is replace by adult Hb, the infant will have what? How can this be counteracted?
A lower efficient than an adult at transferring O2 from lungs to tissues
Infants have higher total Hb concentration in the blood
What are the two models used to describe allosteric effects?
Concerted model
Sequential model
(Probably a mixture for both in most enzymes)
Describe the Concerted model (Monod, Wyman, Changeux)
Recap
Sub-units can exist in only two forms (T and R)
Cannot have mixed molecules
T has a low affinity for the substrate
R has a high affinity for the substrate
Describe co-operativity in the Concerted model
When the substrate binds to T form it caused all sub-units to convert to R form
Why does co-operativity occur in the concerted model?
Because the R form has a higher affinity for substrate than the T form, enzyme activity increases rapidly after each enzyme molecule has bound one substrate molecule
Describe the sequential model (Koshland) (Recap this)
Sub-unite can exist in two forms (T and R)
Can have mixed molecules
T has low affinity for the substrate
R has high affinity for the substrate
Describe co-operativity in the sequential model
When substrate binds to T form it cause the sub-unit to which it binds to convert to R form and makes it easier for substrate to bind to the other sub-units
Why does co-operativity occur in the sequential model?
Because the affinity for substrate increases once one sub-unit has converted to R form, activity increases rapidly after protein has bound one substrate molecule
In both the sequential and concerted model, how do positive effectors act?
Positive effectors stabilise the high affinity form of the sub-units
In both the sequential and concerted model, how do negative effectors act?
Negative effectors stabilise the low affinity form of the subunits
The muscle is made up of:
Bundles of long, thin, multinucleated cells called muscle fibres (myofibres)
What is the cell cytoplasm in the muscle called?
The sarcoplasm
What is the sarcoplasm in the muscle filled with?
Tightly packed structures called myofibrils
What do myofibrils (found in the sarcoplasm) consist of?
A large number of contractile units called sarcomeres
A sarcomere (in myofibrils) is composed of what?
A number of myofilaments of two types:
Light or thin (actin)
Heavy or thick (myosin)
Slide 2, lecture 17
Good diagram of make up of the muscles
What are sarcomeres made up of?
Thick and thin myofilaments in a very specific arrangement leading to characteristic banding pattern
What does a sarcomere stretch between?
2 Z discs
(Following in from the sarcomere stretches between to 2 Z discs) what is attached to each Z disc?
Thin myofilaments projecting away from the Z discs
What are interleaved with thin myofilaments and arranged centrally between, but not attached to, Z discs?
The thick myofilaments
Slide 4, lecture 17
Diagram of Z discs, thin myofilaments and thick myofilaments
What is a major component of the thin filaments?
The protein actin
What is monomeric actin (G actin)
A globular protein
What happens when monomeric actin polymerises?
It forms long strands which then form a two-stranded helical filament (F actin)
Which proteins bind together and attach to the F actin?
Troponin (TN)
Tropomyosin (TM)
How many sub-units does troponin have?
Three
What are the thick filaments composed of?
The protein myosin
What is the protein myosin made of?
Two identical heavy chains and four light chains (2 each of two types)
Describe the make up of the heavy chains of the protein myosin
The tail regions coil around each other with the heads bending away from each other at the neck region
What is the relationship between the light chains and the heavy chains in the protein myosin?
Two light chains are associated with the neck of each heavy chain
The head domains of the heavy chains (I think) of the protein myosin are what?
Specialised ATPases
When myosin molecules aggregate what forms?
A thick filament with heads at either end of the filament and a bare zone with no heads in the middle
What are myofibrils composed of?
Very large numbers of myofilaments arranged in sarcomeres
How is muscle contraction initiated?
By the release of Ca2+ from sarcoplasmic reticulum in response to nerve stimulus
What are the sub-units if troponin?
TN-T
TN-I
TN-C
What does the sub-unit of troponin, TN-C bind to?
Calcium
What happens when calcium binds to the TN-C sub-unit of Troponin
Causes conformational change altering the binding position of tropomyosin to actin
After the binding position of tropomyosin to actin has changed what happens?
Exposes the myosin binding sites on actin
Then myosin binds to actin
What is the first stage in muscle contraction? (Slide 11, lecture 17)
ATP binds to the myosin head causing myosin to lose affinity for actin
What is the second stage in muscle contraction? (Slide 12, lecture 17)
The myosin head folds around the ATP causing flexion at the neck of the myosin molecule. ATP is hydrolysed to ADP and Pi but both initially stay bound. Head binds new actin sub-unit
What is the third stage in muscle contraction? (Slide 13, lecture 17)
Pi released from myosin. This causes conformational change at neck. This is the “Power Stroke” allowing myosin to return to original conformation
What is the fourth stage in muscle contraction? (Slide 14, lecture 17)
ADP is released to complete the cycle
Muscles contract in response to what? (Muscle contraction) (part 1) (Ca2+)
A nerve impulse
Transfer of the signal from nerve to muscle involves what? (Muscle contraction) (part 2) (Ca2+)
A neurotransmitter (Acetylcholine) and changes in cytosolic concentrations of Ca2+ and Na+
Ca2+ is normally what? (Muscle contraction) (part 3) (Ca2+)
Hidden away within the sarcoplasm reticulum of muscle cells
In response to the nerve stimulus, what happens at the muscle? (Muscle contraction) (part 4) (Ca2+)
Ca2+ is released from the sarcoplasmic reticulum and initiates muscle contraction
When stimulation ceases what happens to calcium? (Muscle contraction) (part 5) (Ca2+)
It is taken back into the sarcoplasmic reticulum via a Ca/ATPase
What happens as the impulse flows down a nerve? (muscle contraction) (part 6) (Ca2+)
It results in the opening of sodium channels
What does depolarisation result in? (Muscle contraction) (part 7) (Ca2+)
Results in opening of the voltage-gated Ca2+ channels in the axon terminal
What happens when Ca2+ flows into the axon terminal? (Muscle contraction) (part 8) (Ca2+)
It triggers exocytosis of acetylcholine (normally isolated in vesicles)
Once activated what is the pathway of Ach? (Muscle contraction) (part 9) (Ca2+)
It passes over the synaptic cleft and binds to Ach receptors on surface of muscle cells
What receptors do Ach molecules bind to? (Muscle contraction) (part 10) (Ca2+)
Nicotinic Ach receptor
What happens when Ach binds to nicotinic Ach receptors? (Muscle contraction) (part 11) (Ca2+)
Results in a conformational change forming a channel through which Na+ and K+ can enter the cell
What happens when Na+ enters the muscle through Ach receptors? (Muscle contraction) (part 12) (Ca2+)
It depolarises the membrane
What happens after Na+ enters the muscle through Ach receptors and depolarises the membrane? (Muscle contraction) (part 13) (Ca2+)
The depolarisation spreads and activates voltage gated Na+ channels so that further depolarisation of cell membrane and of lined T-tubules
What happens after the depolarisation has spread in the cell? (Muscle contraction) (part 14) (Ca2+)
This eventually activates a protein in T-tubule membrane which is linked to a Ca2+ channel protein in the sarcoplasmic reticulum
What then happens to the Ca2+ channel in the sarcoplasmic reticulum? (Muscle contraction) (part 15) (Ca2+)
The Ca2+ channel opens and releases Ca2+ into the sarcoplasm where it binds to TN-C
Once the calcium channel opens and releases Ca2+ into the sarcoplasm where it binds to TN-C, what happens? (Muscle contraction) (part 16) (Ca2+)
Sarcoplasmic Ca2+ concentration rises from ~10-7M to ~10-6M
Finally what happens after contraction? (Muscle contraction) (part 17) (Ca2+)
Ca is re-isolated into the sarcoplasmic reticulum using an energy dependent Ca/ATPase pump
Exercise in which the aerobic energy system is the main energy supply, typically lasts how long
30+ minutes
Middle distance events normally lasting between 4-30 minutes, rely on what energy system?
Contributions from anaerobic sources is much larger
Slide 4, lecture 19
Energy use according to exercise duration
In aerobic exercise substrates (carbohydrates and lipids) need to be what? To produce energy
Need to be oxidised
Where is energy derived from during high intensity exercise?
From anaerobic sources; PCr at very rapid intensities and anaerobic glycolysis
Less is derived from intramuscular stores (e.g. glycogen and lipids)
What sort of fibres play a more important role in high intensity exercise?
Type II
Type IIx
Fast twitch muscle fibres
Where is the majority of energy derived from for aerobic exercise?
Lipids, carbohydrates (and some proteins)
What sort of muscle fibres play a more important role during aerobic exercise?
Type I ‘slow twitch’ muscle fibres play a more important role
Energy use during aerobic exercise is dependent upon what?
Intensity of exercise
At lower exercise intensities energy is mostly derived from what fuel source?
Lipid sources
At higher exercise intensities, there is a greater contribution from what energy source?
Carbohydrate sources
Fat utilisation during exercise peaks when?
Around 65% of VO2max and declines there after
The amount of fat that can be oxidised during exercise can be increased with what?
Training
Why does lipolysis slow at high exercise intensities? (First reason)
- There is a reduced blood flow to adipose tissue
As a result, free fatty acid delivery to the exercising muscles is inhibited, limiting the oxidation rates
Why does lipolysis slow at high exercise intensities? (Second reason)
Fatty acids require 15% more oxygen to breakdown
What is one of the major reasons we cannot oxidise fat at higher exercise intensities?
The amount of carnitine which is needed to shuttle FFA into the mitochondria for oxidation I’d reduced - so it is a transport into the mitochondria issue
Recap slides 13&14, lecture 19
What happens at higher exercise intensities
As fat oxidation decreases, what happens to the rate of carbohydrate oxidation?
The rate of carbohydrate oxidation increases
Where do carbohydrates come from? (In our body)
Glycogen stores in muscle and liver
What is glycogenolysis?
The break down of glycogen in the liver and muscle
What enzyme is glycogenolysis regulated by?
Glycogen phosphorylase
Regulation of glycogenolysis during exercise depends on what?
The energy status of the cell
Slide 19, lecture 19
Not sure what it is
What is another important enzyme that regulates glycogenolysis (or carbohydrate oxidation) (Check this)
Pyruvate Dehydrogenase
When does PDH increase?
During very high intensity exercise
What is PDH important for?
Catalysing Acetyl CoA (which is needed for the TCA cycle and more energy)
Slide 22, lecture 19
Not sure what it is
What is the most likely candidate for fatigue?
Glycogen depletion
As glycogen depletion is a likely candidate for fatigue what could be beneficial to performance?
A constant supply of carbohydrates
Hence why elite endurance athletes consume high carbohydrate diets
Slide 25, lecture 19
Example of how a good level of carbs can help
What are the key non-steroid hormones involved in exercise?
Adrenaline Noradrenaline Insulin Glucagon Growth hormone Insulin like growth factor-1
During aerobic exercise, an increase in catecholamines, glucagon and growth hormone result in what?
An increase in glycolysis, glycogenolysis and lipolysis
During aerobic exercise, as exercise duration increases, what else increases?
Gluconeogenesis
Ketone bodies
Fatty acids
During an aerobic exercise, an increase in insulin results in what?
Decreased gluconeogenesis lipolysis
Decreases in ketone bodies, growth hormone, catecholamines, fatty acids, glycerol
What are the key steroid hormones involved in exercise?
Cortisol
Testosterone
Oestrogen
Progesterone
During aerobic exercise, an increase in cortisol results in an increase in what?
Gluconeogenesis and lipolysis
What is gluconeogenesis
The generation of glucose from some non-glucose sources
What happens to oestrogen, progesterone and testosterone during exercise?
Oestrogen and progesterone increase
Testosterone decreases
After exercise, what happens to: testosterone, growth hormone and insulin (after eating) and what does this cause?
They all increase
This causes protein synthesis
After exercise, what happens to: cortisol and glucagon and what does this cause?
They increase
This causes protein degradation
What is co-operativity in the converted model?
When substrate binds to T form it causes all sub-units to convert to R form
What is a major difference between the concerted and the sequential model?
The concerted model says that when one sub unit binds to the substrate, all sub units swap from T to R
The sequential model says that the change is more sequential, so when T binds to the substrate, then it is converted to R and it is a more gradual change
As exercise intensity increases, ATP turnover increases, what does this result in? And what does that stimulate?
ADP, AMP, Pi
Stimulates glycogenolysis
As exercise duration increases, glycogen stores deplete, this results in a decrease in what? Increasing reliance on what?
Decrease in glycolic flux
Increased reliance on lipolysis
