Biochemistry Flashcards
What is glycogen?
Storage molecule for carbohydrates
What is glycogenesis?
Synthesis of glycogen from glucose
What is glycogenolysis?
Breakdown of glycogen to glucose
What enzyme controls glycogenesis?
Glycogen synthase
What enzyme controls glycogenolysis?
Glycogen phosphorylase
Where is glycogen the main storage molecule of glucose?
Liver and muscle cells
What is the same and what is the difference between glycogen in liver and muscle cells?
Same molecule- different function
When is glycogen broken down to glucose in the liver?
In between meals to maintain blood glucose levels for cells
When is glycogen from muscle cells used and how is glucose formed here?
During bursts of physical activity- through glycolysis and TCA cycle
What is gluconeogenesis?
Formation of glucose from non-carbohydrate precursors
When does gluconeogenesis occur?
When liver cannot produce glucose- prolonged starvation
What binds glucose molecules together to form glycogen?
Alpha 1,4 linkages
What are the branches of glycogen formed by?
Alpha 1, 6 linkages
What do alpha 1, 4 linkages form between?
1C carbon of a glucose and a 4C carbon of another
What do alpha 1, 6 linkages form between?
1C carbon of a glucose and a 6C carbon of another
What increases how fast glucose can be synthesised or broken down?
The more ends the molecule has
What is the protein at the centre of glycogen known as?
Glycogenin
What does glycogenin do?
Binds 4 glucose molecules to itself
What does glycogenin with glucose attached act as?
A precursor for glycogen production
What has to happen to glucose to make glycogen?
Phosphorylated
What is formed from the phosphorylation of glucose?
Glucose-6-phosphate
What enzyme catalyses the phosphorylation of glucose?
Hexokinase
What must happen to glucose-6-phosphate in order for it to form either glucose or glycogen?
Transformed to glucose-1-phosphate
What enzyme moves the phosphate in from C6 to C1?
Phosphoglucomutase
What is the substrate for glycogen synthase?
UDP-glucose
What happens in terms of ATP for every added glucose molecule to form glycogen?
1 ATP is consumed
Where is glucose attached to UDP?
2nd phosphate group
What is the glucose phosphate bond in terms of energy?
High energy
What does the enzyme transglycosylase do?
Introduces alpha 1, 6 glycosidic branches into glycogen
What is the product of glycogen breakdown?
Glucose-1-phosphate
After glucose-1-phosphate has formed glucose-6-phosphate in glycogenolysis, what can this do?
Be dephosphorylated in the liver to release glucose into the bloodstream or not be dephosphorylated in muscle
How is glucose formed in the liver transported into the bloodstream?
GLUT2
What does insulin stimulate?
Glycogen synthase
What does insulin inhibit?
Glycogen phosphorylase
What does glucagon stimulate?
Glycogen phosphorylase
What does glucagon inhibit?
Glycogen synthase
What do adrenaline and cortisol stimulate?
Glycogen phosphorylase
What happens in glycogen storage disease?
Increased glycogen deposits in the liver, muscle, both
What are some precursors for gluconeogenesis?
Lactic acid, amino acids, glycerol
When is lactic acid synthesised?
By skeletal muscle under anaerobic conditions
Where are amino acids derived from?
Muscle protein by proteolysis
Where is glycerol derived from?
Triglycerides by lipolysis in adipose tissue
What is gluconeogenesis in terms of energy?
Energy consuming
Where does gluconeogenesis occur?
Liver or small amounts in the kidneys
Is gluconeogenesis the opposite of glycolysis?
Almost, but not
What does gluconeogenesis require?
4 unique liver enzymes
What does gluconeogenesis proceed via the synthesis of?
Oxaloacetate in the mitochondria
What energy does gluconeogenesis use?
4 ATP and 2 GTP
What type of amino acids cannot be used for gluconeogenesis?
Hetogenic
What type of amino acids can be used for gluconeogenesis?
Glucogenic
What does glucagon show?
A need for glucose- stimulates gluconeogenesis/inhibits glycolysis
What does insulin show?
Too much glucose- stimulates glycolysis/inhibits gluconeogenesis
What does a high AMP or ADP signal?
need for energy- breakdown glucose
What does high ATP signal?
Gluconeogenesis
What do high concentrations of fructose 2, 6 biphosphate, citrate, alanine and acetyl CoA signal?
Gluconeogenesis
What does increased aft intake with no energy expenditure result in?
Increased adipocytes and increased fat in adipocytes
What can fat deficiency lead to?
Membrane disorders, increased skin permeability and mitochondrial damage
What are fat soluble vitamins?
ADEK
Where are fat soluble vitamins stored?
In body fat
What can fats otherwise be known as?
Lipids
What are simple lipids?
Fatty acids and triglycerides
What are compound lipids?
Phospho or glycolipids
What is cholesterol and example of?
A steroid
What part of lipid structure makes them insoluble in water?
Long chain fatty acids
What is the main energy form in adipose tissue and dietary fat?
Triglycerides
What do triglycerides consist of?
3 fatty acids and glycerol
Describe saturated fatty acids?
No double bonds
Describe unsaturated fatty acids?
Single double bond
Describe polyunsaturated fatty acids?
Many double bonds
What formation are the double bonds of fatty acids usually in?
Cis isomer
What type of fatty acids have their double bond 3 carbons from the end of the chain?
Omega 3 fatty acids
What are the main products of fat digestion?
Glycerol, fatty acids and monoglycerides
Where is glycerol absorbed?
Intestinal epithelial cells
Short/medium chain fatty acids enter the portal system straight away. What must long chain fatty acids become first?
Triglycerides
How do triglycerides enter the blood?
Combine with other lipids and proteins to form chylomicrons which enter the lymph system and then blood
What can happen to free fatty acids when they arrive at tissues?
Resynthesised to triglycerides for storage or oxidised to produce energy on muscle cells
What is lipolysis?
Breakdown of lipids
What do fatty acids have to be converted to before they can be oxidised to form energy? Where does this happen and what does it require?
CoA derivatives- in the cytoplasm and requires 2 ATP
Where does further oxidation take place?
Mitochondrial matrix
What facilitates transport of fats converted to CoA derivatives from the cytoplasm to matrix?
Carnitine shuttle- acyl CoA in matrix
Where is the beta oxidation cycle of reactions?
Mitochondrial matrix
What is the substrate for beta oxidation?
Acyl CoA
What is formed when Acyl CoA is shortened by 2 carbons?
1 Acetyl CoA and a shortened acyl CoA, 1 FADH2 and 1 NADH + H+
What is formed at the end of the beta oxidation pathway?
2 Acetyl CoAs
What types of fats require additional enzymes to be oxidised?
Unsaturated, odd chain and branched chain
What enzyme activates glycerol to glycerol 3 phosphate?
Glycerol kinase
What is glycerol 3 phosphate dehydrogenated to?
Dyhydroxyacetone phosphate
What are ketone bodies associated with?
Oxidation of fats
Where are ketone bodies formed and from what?
Liver mitochondria from Acetyl CoA
What makes ketone bodies be generated?
Lots of acetyl CoA
What problem to ketone bodies cause?
Oxaloacetate is consumed for gluconeogenesis
What does increased ketone bodies in the blood cause?
Acidosis, loss of function, acidic coma, death
Ultimately fat is broken down to form what?
ATP
What is lipgenesis?
Fatty acid synthesis
Where does lipogenesis mainly take place?
Liver
What type of redox process is lipogenesis and so what is required?
Reductive process- electrons are required
What is the substrate for lipogenesis?
Acetyl CoA
Where specifically in liver cells does lipogenesis take place?
Cytoplasm of cells
What facilitates the transport of acetyl CoA from the mitochondrial matrix to the cytoplasm?
Citrate
What is Acetyl CoA converted to before fatty acids are synthesised?
Malonyl-CoA
What is Malonyl CoA responsible for?
Giving carbon to fatty acids
What enzyme converts acetyl CoA to malonyl CoA?
Acetyl CoA carboxylase
What is the only type of fatty acid synthesised through fatty acid synthase?
Long chain saturated
What is the source of electrons for lipogenesis?
NADPH
What is the function of acyl carrier protein contained in fatty acid synthase?
The growing chain is attached to it
When does fatty acid synthase stop having an effect?
Once the chain is 16C in length
In lipogenesis, further enzymes are required to do what?
Elongate the chains or add to double bonds
When are levels of Palmitoyl CoA high?
Excess fatty acids
What has to be present for synthesis of triglycerides?
Glycerol 3 phosphate
What produces glycerol 3 phosphate and from what?
Liver from glucose
Are all amino acids converted to Acetyl CoA?
No
Can all amino acids be oxidised in the TCA cycle?
Yes
What happens to amino acids if they are not used?
They are degraded in the liver
What does amino acid breakdown produce which has to be removed?
Nitrogen (originally ammonia and ammonium ions)
What is the major nitrogen containing excretory molecule?
Urea
Where is urea formed?
Liver
How many nitrogens does urea have?
2
In all tissues, the first stage of amino acid catabolism is what?
Amino group is transferred onto a heto acid- usually forms glutamic acid
The second stage of amino acid catabolism which occurs in the liver is what?
Removal of amino group from glutamic acid to form free ammonia
How is an amino acid transported to the liver?
Glutamate is transferred to pyruvate to give alanine
Where are the main transporters of nitrogen?
Blood
What is the carbon found in urea derived from?
CO2
What are the products of urea production?
Urea and a by product which can enter the TCA cycle
After the removal of the alpha amino group, what are the remaining carbons converted to?
Major metabolic intermediates
What are ketogenic amino acids degraded to?
Acetyl CoA- can give rise to ketone bodies and fatty acids
What are glucogenic amino acids degraded to?
Pyruvate/TCA cycle intermediates- can give rise to glucose
Glucose is our primary energy source which is oxidised to?
CO2 and H2o
What 3 pathways can glucose take?
- Pentose Phosphate pathway (oxidation)
- Fermentation by anaerobic glycolysis
- Oxidation through aerobic glycolysis
What is formed from glucose through the pentose phosphate pathway and what does this do?
Ribose-5-phosphate: precursor for nucleotide synthesis and DNA repair, essential for growth
What is formed from glucose through anaerobic glycolysis and what does this do?
Lactate- rapid, inefficient production of ATP
What is formed from glucose through aerobic glycolysis and what does this do?
Pyruvate- efficient ATP production
What two ways can glucose be transported into cells?
Glucose/Na+ co-transporters or passive facilitated diffusions
Which GLUT transporters are found in the brain and have a low Km?
GLUT1 and GLUT3
Describe GLUT2?
Found in liver and beta cells, high Km and is insulin dependent
Describe GLUT4?
Found in muscle and adipose tissue and is insulin dependent
Describe GLUT5?
Fructose transport in the gut
What is formed in glycolysis?
2 pyruvate, 4ATP, 2H2O, 2NADH, 2H+
What enzyme controls substrate entry in glycolysis?
Hexokinase
What enzyme controls rate of flow in glycolysis?
Phosphofructokinase
What enzyme controls product exit in glycolysis?
Pyruvate kinase
What are 3 inhibitors of glycolysis?
ATP, citrate, H+
What is used to ferment pyruvate to lactate in anaerobic conditions?
NADH
When is NADH regenerated in glycolysis?
Beginning of stage 3
Catabolism of pyruvate must cause reduction of what to what?
NAD+ to NADH + H+
How is NAD+ regenerated?
Oxidative metabolism of pyruvate
Where does the TCA cycle occur?
Mitochondrial matrix
How does pyruvate enter the mitochondrial matrix?
By an H+ gradient from the cytosol
What does pyruvate dehydrogenase complex catalyse?
Oxidation of pyruvate to acetyl CoA
Is pyruvate oxidation to acetyl CoA reversible?
No
How many reactions are there in the TCA cycle?
8
2C acetyl CoA combines with 4C ? to form citrate?
Oxaloacetate
What happens to 6C citrate in the TCA cycle?
It is decarboxylated twice to form CO2
What does the TCA cycle yield in terms of electron donors and energy?
1 GTP, NADH+H+, FADH2
All enzymes of the TCA cycle are located in the mitochondrial matrix except 1. What is this and where is it found?
Succinate dehydrogenase- inner mitochondrial membrane
In oxidative phosphorylation, NADH and FADH2 are used to form what and how?
Reduction of O2 to H2O
The energy created in the reduction reaction of O2-H2O is used to do what in oxidative phosphorylation?
Pump proteins from the matrix to the intermembrane spaces
What is used to phosphorylate ADP to ATP in oxidative phosphorylation?
Energy of proton flow
What are used to help NADH across the mitochondrial membrane?
Malate aspartate shuttle and glycerol-3-phosphate
What are cytochromes?
Proteins with a haem group as a co-factor which can take up and release electrons
