Week 8: Vitamins and metabolic energy Flashcards
What are the classes of vitamins?
A, B, C, D, E and K
What are the types of B vitamins?
(1,2,3,5,6,7,9,12)
What is B2 also known as?
Riboflavin
What is B7?
Biotin
What are the two classifications of vitamins?
Water-soluble or lipid soluble
What vitamins are excreted via the urine?
B
What is an apoenzyme
Enzyme without its coenzyme
What vitamins are water soluble?
- Vitamin C and B
Where are lipid soluble vitamins stored?
In the liver and adipose tissue
What is carotene?
The precursor (pro-vitamin) of vitamin A
How is carotene converted to vitamin A
β-carotene 15,15’-dioxygenase
What are the roles of vitamins?
-Converted into co-enzymes
-Act as hormones
-Act as antioxidants
What can vitamin C (ascorbic acid) act as?
A metal co-factor , it can move electrons. Hydroxylation of collagen – returns Fe to reduced state
It is present in cytochrome a & c of respiratory chain
What is the role of vitamin C in collagen production?
Vitamin C’s role is to help bind the Fe3 state to the oxygen and return to the reduced Fe4 state
If deficient the Fe 3 state cannot be reduced so no hydroxylation of collagen
What is the role of vitamin C in collagen production?
Vitamin C’s role is to help bind the Fe3 state to the oxygen and return to the reduced Fe4 state
If deficient the Fe 3 state cannot be reduced so no hydroxylation of collagen
What sources of food is B2 found in?
Eggs, meat, dairy and vegetables
What vitamin is present in the FAD structure?
B2
What binds to Protoporphyrin IX?
FAD
What vitamins are commonly known as the hormone vitamins?
Vitamin D and A
What type of hormone is vitamin D3 and what is its biologically active form
steroid hormone- calcitrol
What are the two routes that cells obtain energy from?
-Phototrophs
-Chemotrophs
What are the two types of metabolic pathways
Anabolic and catabolic
What are the two key characteristics of metabolic pathways
- They are irreversible
- The reaction must be highly favoured thermodynamically so that you do not get both products and reactants that will stop the flow of reaction pathways
- They are very specific
- The reactions must give only one particular product from the reactants. This allow regulation by enzymes etc
What does it mean if the value is closer to 1, less than 1 or more than 1
1= equal concentrations of reactants and products
>1= irreversible forward reaction
<1= irreversible reverse reaction
What causes a spontaneous reaction?
Reactions that give out energy + reactions that increase disorder
Why do reactions that are exergonic spontaneous?
Because the products they make are of lower energy, as they make many chemical bonds (the internal energy changes). We can measure and determine changes in internal energy or enthalpy (∆H) as a reaction proceeds
Why do reactions that increase entropy cause a spontaneous reaction?
∆G = ∆H - T∆S, because the gibbs free energy is more likely to be negative
What is an exergonic reaction and an endergonic reaction?
- Exergonic = When a reaction proceeds in a release of free energy
- Endergonic = if the free energy of a reaction is negative
Are catabolic or anabolic reactions more likely to be spontaneous?
Catabolic
- They are more likely to be spontaneous as you are breaking up molecules which leads to an increase in entropy.
- But you start with a very stable molecule, so the activation energy is high, which means the reaction may be reversible
What is the BMR?
Basal metabolic rate
-Amount of energy the body needs to maintain normal functions such as breathing, steady heart, blood circulation, grow and repair of cells and tissue, and maintain healthy hormone levels.
What is thermogenesis?
Describes the thermic effect of food. These include eating, swallowing, digest (chemically and mechanically breaking down of food as it moves along the GIT),
What are activated carriers?
- They are small molecules responsible for the storage of energy and electron transfer for energetically unfavourable reactions
- These energies are either stored in bonds (bond formation) or as high energy electrons (released via oxidation reaction)
In what form is energy stored in activated carriers?
- These energies are either stored in bonds (bond formation) or as high energy electrons (released via oxidation reaction)
Give an example of an activated carrier
Phosphoryl transfer, ATP acts as the activated carrier for the phosphoryl group
What is the role of NAD
Nicotinamide adenine dinucleotide transfers electrons in aerobic respiration. Reduced form NADH
What is the reactive group in coenzyme A?
The thioester group (C-S)
What are the two major aspects of metabolism using activated carriers?
- The metabolic reactions react slowly in absence of a catalyst
- A wide range of metabolic tasks are accomplished by a small set of carriers
What are the bonds called in ATP?
The triphosphate unit contains two phosphoanhydride bonds.
What are the 6 classes of metabolic reactions?
- Oxidation-reduction reactions
-Ligation reactions
-Isomerization reaction - Group transfer reactions
-Hydrolytic reactions
-Addition or removal of functional groups to form double bonds
Give an example of a reaction for both FAD and NAD+
Succinate + FAD -> Fumarate + FADH2
Malate + NAD+ -> Oxaloacetate + NADH + H+
Give an example of a ligand reaction
The formation of C-C bonds in the formation of oxaloacetate from pyruvate
Give an example of an isomerization reaction
Conversion of citrate to isocitrate
Name 3 ways to regulate metabolism
By controlling:
- Amount of enzyme
-Catalytic activity
- Accessibility of substrate
What are the 3 stages in the generation of energy from food?
Stage 1: large molecules in food are broken down into smaller units through a process of digestion
Stage 2: these numerous small molecules are degraded to a few simple units that play a central role in metabolism.
Stage 3: ATP is produced from the complete oxidation of the acetyl unit of acetyl CoA.
What is the structure of haemoglobin
tetrameric protein with 2
identical alpha subunits and 2 identical beta
subunits
Structure has a α2β2 configuration
Each globin subunit contains a Haem (Heme)
What does the haem group have?
Haem cofactor is a Tetrapyrrole ring
molecule in association with an Fe2+ ion
What occurs when oxygen binds to haem group
Fe2+ lies outside plane of tetrapyrrole ring
On binding Fe2+ moves into plane of ring to become flat
A distal Histidine residue helps to stabilize the
bound O2 by forming a hydrogen bond
What are the differences and similarities between the myoglobin and haemoglobin oxygen binding curve?
- Myoglobin has the highest affinity (higher Km)
- Both have the same Vmax (all oxygenated haemoglobin or myoglobin)
- Haemoglobin has a S-shaped curve - which is characteristic to an allosteric binding protein. This is important for the unloading of the oxygen
- Haemoglobin releases oxygen more readily
What are the differences and similarities between the myoglobin and haemoglobin oxygen binding curve?
- Myoglobin has the highest affinity (higher Km)
- Both have the same Vmax (all oxygenated haemoglobin or myoglobin)
- Haemoglobin has a S-shaped curve - which is characteristic to an allosteric binding protein. This is important for the unloading of the oxygen
- Haemoglobin releases oxygen more readily
Why does the myoglobin need to have a higher affinity for oxygen than haemoglobin?
Because in the muscle tissue the haemoglobin needs to release the oxygen to the myoglobin
Why is haemoglobin a more efficient oxygen carrier?
Due to cooperative binding to O2 to Haemoglobin
- Binding of O2 Haem in one subunit increases affinity of O2 to others
Cooperativity also applies to O2 unloading
What subunit changes in oxygen binding to haemoglobin?
O2 causes change in tertiary structure
α1β1 dimers rotate relative to α2β2 by 15°
What is the deoxygenated state of haemoglobin called?
The Tense (T) state - low oxygen affinity
What is the oxygenated state of haemoglobin called?
- In R state O2 binding sites are open and are more able to bind O2
What are the 2 models used to explain cooperative O2 binding?
- Concerted model
- Sequential model
What is the difference between the concerted model and sequential model
In the concerted model all o2 bound forms either T and R states, whereas sequential model describes the idea that individual subunits shift. Allows neighbouring subunit to bind O2 with slightly higher affinity
Does pure haemoglobin bind more or less strongly to O2 than haemoglobin in the blood?
Pure haemoglobin binds more strongly
- This is because when haemoglobin is in the blood it still needs to be able to release the oxygen
- Important that T-state must be stabilised or
Haemoglobin would never release O2
What is 2,3 Bisphosphoglycerate (2,3 BPG)?
-An allosteric regulator
-2,3 BPG binds to T form and stabilises it, reduces the oxygen binding capacity. Stops the haemoglobin holding to the oxygen too tightly
Does foetal haemoglobin have a high or low affinity for 2,3 BPG?
‼️Low affinity for 2,3 BPG, more haemoglobin in the relaxed state
Increased oxygen affinity compared to mother
What is the Bohr effect?
Respiring tissues produce CO2, lower pH (from the carbonic acid and lactic acid breakdown) - more oxygen is needed- they decrease the oxygen affinity to haemoglobin
What is the effect of CO2 and Increased pH
Tense state is stabilized
How does a decreased pH affect the T state?
Stabilizes it by allowing formation of salt bridges within globin subunits
As the pH drops the proton binds onto the histidine ring (pKa of histidine is 6- pH), forms hydrogen bond and stabilizes it
What are the 2 ways that CO2 can affect haemoglobin ?
Increased CO2 leads to decreased pH through
action of carbonic anhydrase
CO2 also directly effects quaternary structure of haemoglobin
How does CO2 directly affect the quaternary structure of haemoglobin?
Reacting with amino termini to form negatively charged carbamate
Amino termini of subunits lie at αβ interface
Carbamate groups allow formation of salt bridges that stabilize T state
What is the Haldane effect?
Reverse of the Bohr effect,
The more oxygenated the environment is the less binding affinity it has to bind with carbon dioxide
What form of carbon dioxide is found the most in the blood?
- In bicarbonate (around 70%)
- 23% in carbaminohemoglobin
- 7% Dissolved in solution
- None in the carbonic acid state because it deprotonates to bicarbonate at physiological pH
