Human metabolism: carbohydrates, fats and proteins Flashcards
Dietary mono and di-saccharides offer readily available glucose and causes a rapid raise in blood glucose.
Name an example of a
I) Monosaccaride
II) Disaccaride
Mono: Glucose, fructose (honey/friuts)
Di: Sucrose (glucose and fructose) Lactose (glucose, galactose)
Are plant and animal starches broken down into glucose?
Yes but they take much longer to be digested
Why is glucose a versatile fuel?
Can be consumed by all tissues
Can be respired anaerobically (unlike fats and proteins)
What is the initial pathway for all glucose metabolism in the cytoplasm?
Glycolysis - starts with anaerobic pathway whereby glucose (6 carbon) is converted into 2 x pyruvate (3 carb) and 2 moles of ATP by substrate level phosphorylation.
Under anaerobic conditions what happens to the pyruvate
Reduced to lactate and regeneration of NAD+ form NADH (NAD+ needed in glycolysis)
Under aerobic conditions what happens to pyruvate?
Oxidative phosphorylation in the mitochondrion, pyruvate (3 carbon) is converted into the acetyl coenzyme A (CoA).
Acetyl coenzyme A is then consumed into the krebs cycle
What does the krebs cycle create? Why is this significant?
- 3 x NADH
- 1 X FADH2
- 1 X GTP
- 2 x CO2
Reduced 1 & 2 pass electrons does transport chain to produce ATP
How much ATP is made from each mole go glucose + ATP in
1) Aerbic respiration
2) Anaeorbic respiration
Aerobic 30-32moles (16 times more, due to electron transport chain), 20 ATP
Anaerobic 2 moles, 5 ATP
Why are red blood cells reply on anaerobic respiration
They continue no intracellular organelle such as mitochondria so they ca squeeze through capillaries.
Therefore no oxidative phosphrylation
What substrates fuels can be used for anaerobically respiting muscle?
Blood glucose (usually from lover glycogen) Muscle glycogen
Why can fat stores never be converted to glucose?
Fat stores can be broken down to acetyl coenzyme A (for the aerobic krebs) but it cannot be converted back to pyruvate
Which organ needs a lot of sugar?
The brain 100g/day
In starvation where us glucose obtained from?
Muscle protein and amino acids
Cause muscle wasting
For a non-diabetic what is the normal range of blood glucose levels
4-8 mol/l
Below which blood glucose level is a person at risk of hypoglycaemic coma?
2mmol/l
How is fat stored in the body?
Triacylglycerol which forms liquid droplets in the cytosol of the adipocyte.
How is energy produced from triacylglycerol (TAG)
Fatty acids side chains are long with many hydrogen ions, there act as a reservoir for reducing co factors NADH and FADH2 along the electron transport chain.
Fat has higher energy yield than carbohydrates
What hormones catalyse the HSL enzyme which breaks down TAG to free fatty acids y
Noradrenaline
Adrenaline
Glucagon
Therefore blood fatty acids raised in starvation, stress, exercise, diabetic coma and GDM
Which pathway in high aerobic tissue causes oxidation of fatty acids
beta-oxidation pathway - Fatty acid combines with co-enzyme A - fatty acyl coenzyme A, then the carbon fatty acid is nippled away producing FADh2 and NADH
What is the main difference between fat & carbohydrate storage
Carbohydrate are limited and only stored for 24 hours
Fat can be stored in limitless quantities
What is the issue with starvation and brain function
Brain has high glucose requirement. After 24 hours, bodies predominant fuel is fats. Fats limited as fat cannot be converted into glucose. Brain cannot consume fatty acids as lipoproteins do not cross the BBB.
As fat acid can be converted into acetyl co enzyme which substrate of the krebs cycle must increase and where does it come from
Oxaloacetate (amino acids, muscle protein)
What drives ketogensis in the liver in starvation
Oxaloacetate is withdrawn from the krebs cycle for gluconeogenesis but rates of fatty acid uptake and beta-oxidation remain high.
Therefore the liver channels excess acetyl coenzyme A into ketogenesis
Ketones are then released into the bloods which can then be used by the brain
How does the response to insulin change in pregnancy?
Initial increase in insulin sensitivity
Mild insulin resistance develops can be reduced by 50-70% by 3rd trimester
- if become more severe → GDM
In GDM what happens to serum levels of
- insulin
- fatty acids
- ketones
- Normal or raised
- high
- high (increased ketonuria
Why is GDM associated with macrosomia
High levels of glucose uptake in innate. Glucose uptake is predictive of birth weight
What the 2 situations proteins are broken down into amino acid
- High oral intake (cannot be stored)
2. Starvation - amino acids for glucose synthesis.
How is the nitrogenous amino group excreted from amino acid?
Why is this important?
Amino acid metabolism is initiated with the removal of the nitrogenous amino group which is then incorporated into urea in the hepatic urea cycle.
Important to prevent the build up of toxic nitrogen compounds such as ammonia (NH4+)
How are amino acids converted into ammonium
Tranamiantion and deamination of glutamate
- Deamination amino group transferred to alpha-ketoglutarate to glutamate
- Deamination Amino acid released as NH4+
**many other tranaminases for individual amino acids
What is the purpose of the urea cycle and where does it occur?
Where is urea excreted
Detoxify NH4+ (2 moles of nitrogen to 1 mole of urea)
Cytoplasm and mitochondria of liver cells
Urea is excreted by the kidneys
What is the urea equation
NH4+ + Bicarb + Aspartate → (using 2 ATP) urea + fumarate
Fumarate → Krebs intermediate
How do high levels of ammonia present
swelling of brain, lethargy, mental restrication
High levels push equation to left (high levels of
Can amino acids be converted into glucose in starvation
Only the gluocgenic amino acids which links in with krebs intermediates
Most muscle tissue releases
alanine → Pyruvate
glutamine → Alpha ketoglutame
What is ketogensis
Ketogenesis is the biochemical process through which organisms produce ketone bodies by breaking down fatty acids and ketogenic amino acids.
How does the liver manage low glucose levels in starvation
Gluconeogenesis (glucagon and cortisol)
Ketogenesis
Protein metabolism
What is phenylketonuria?
Rare condition (1 in 10000) are born without the enzyme phenylalanine hydroxylase, leading to high levels of phenylalanine.
If untreated competitive for amino acid transporters and effect the developing brain leading to gross mental restriction.
When is phenylketonuria test for? Treatment?
Day 6-14 after birth, guthrie test
Diet with low phenylketonuria until age 11 & in pregnancy whilst brain is developing
As the glucose requirements of the foetus increase what energy fuel is used instead
Fatty acids and ketone bodies
insulin resistance in mother
In breast feeding which metabolic pathway is slow to develop?
Lipogenesis (Acetyl CoA converts to triglyercaide for fat storage)
High levels of fat from breast milk, lipoprotein lipase used in lots of tissue so fat is used as energy sorce
Why is brown fat adipose tissue important in newborn?
Newborns cannot shiver
Brown adipose can produce heat from fatty acids - non shivering thermogenesis
