Carbohydrates- Glycolysis Flashcards
What are the dietary forms of carbohydrates?
Starch, sucrose, lactose fructose and glucose
What hormone is released after eating?
Insulin
What does insulin do?
- Stimulates the formation of glycogen from glucose
- Involved in glucose storage and immediate use of glucose after eating
When is glucagon released?
- A while after eating, when glucose levels have dropped in the blood
- Stimulates breakdown of glycogen into glucose
What type of receptor is the insulin receptor on cells?
Tyrosine Kinase Receptor
What do Ras/kinase pathways do?
Control gene expression involved in glucose metabolism
What are the glucose transporters?
- Family of transporters
- GLUT-1 to 4
What is the role of each GLUT transporter?
- GLUT-1: erythrocytes, BBB and foetal
- GLUT-2: bidirectional transporter found in liver, kidney and pancreatic beta cells
- GLUT-3: Nuerons
- GLUT-4: dependent on insulin, adipose tissue and skeletal muscle
What is a sodium dependent glucose transporter (SGLT) and how is it different?
- Energy requiring glucose transporter that moves glucose against a concentration gradient
- Movement coupled to sodium conc. which is co-transported, occurs in intestinal epithelium, renal tubules and choroid plexuses
What happens to excess carbohydrates in the fed state?
- Taken up by liver and converted into fats
- Packaged into vesicles and stored in adipose tissue
- Occurs when you eat beyond energy requirements
What happens to glucose in the fed state?
- Transported to the liver and brain
- Converted to Acetyl CoA and entered into TCA cycle
- Red blood cell consistently takes up glucose
What happens to glucose in red blood cells in the fed state?
- Has no mitochondria
- Glucose does not enter TCA cycle
- Produces some localised ATP through anaerobic respiration
What happens to glucose in muscles in the fed state?
- Generate a glycogen reserve for themselves
- Stores glycogen for future immediate use
When does the basal state occur?
- A short while after eating
- Glucose levels in the blood would have diminished by the point
Where does excess glucose go in the basal state?
- Adipose tissue and muscles
- Similar to fed state
Describe and explain the levels of insulin and glucagon in the basal state
- Insulin decreased
- Glucagon increased in order to draw glucose from glycogen stored
What happens in the liver in the basal state?
- Glycogen reserves are used to maintain blood sugar levels
- Maintenance and prevention of hypoglycaemia
What happens in the brain in the basal state?
- Uses glucose from the blood
What happens in red blood cells in the basal state?
- Converts glucose to lactate
- Lactate goes back to the liver and converts back to glucose
- Lactate cycels
What happens in adipose tissue in the basal state?
- After glycogen stored run out, this is where glucose comes from
- Glycerol in fats is converted into glucose (2 to 1)
- Fatty acid tails are taken up by tissues that need energy are therefore metabolised
What happens in adipose tissue in the prolonged fast state?
- No glycogen left so adipose must be used
- Glycerol is used as raw material
What happens to muscle protein in the prolonged fast state?
- Can be used as fuel for glucose and access of other amino acids
- Does not tend to compromise overall health unless used excessively
What happens in the brain in the prolonged fast state?
- Relinquishes its need for glucose and requires ketone bodies instead
- Preference for glucose diminishes as red blood cells need it more
What molecule are glucose, amino acids and fatty acids converted to for respiration?
Acetyl CoA
What is the importance of Acetyl CoA in respiration?
- Enters the TCA Cycle for complete oxidation to carbon dioxide
- As fuels are oxidised, electrons are transferred to oxygen via electron transport chain to form water
- Energy used to generate ATP
Describe glycolysis
- Splitting of glucose
- First stage of glucose oxidation
- Can happen aerobically/anaerobically
What type of respiration do red blood cells undergo?
Anaerobic respiration
What are oxidation and reduction?
- Oxidation- loss of electrons/hydrogen
- Reduction- gain of electrons or hydrogen
What is NAD?
- Nicotinamide Adenine Dinucleotide
- Co-enzyme found in all living cells
- Contains 2 nucleotide- one with adenosine ring and one with nicotinamide
What is the role of NAD+ in metabolism?
- Involved in redox reactions
- Carrying electrons from one reaction to another
Describe NAD+ as an oxidising agent
- Accepts electrons from other molecules
- Becomes reduced- this reactions forms NADH
Describe NADH as a reducing agent
- Donates electrons to electron transport chain
- Forms NAD+
What does aerobic glycolysis require?
- Mitochondria
- Presence of oxygen
How much ATP is produced from aerobic respiration?
- Plentiful supply- around 36 moles
- Preferential way
Describe the first step in aerobic glycolysis
- Glucose-> Glucose-6-phosphate-> fructose-6-phosphate
- This reaction uses one molecule of ATP
Describe the second step in aerobic glycolysis
- Fructose-6-phosphate-> fructose-1,6-bisphosphate
- This reaction uses on molecule of ATP
Describe the third step in aerobic glycolysis
- Fructose-1,6-bisphosphate splits into two molecules of phosphoglyceraldehyde (PGA)
- Each molecule PGA gets converted into pyruvate
- This in total requires 2xNAD->NADH
- and 2x2ATP –> 2 ATP
Describe what happens in the link reaction between glycolysis and TCA cycle
- Pyruvate to Acetyl CoA
- Uses enzyme pyruvate dehydrogenase
- Also NAD–> NADH
What are the consequences of pyruvate dehydrogenase deficiency?
- Neonates
- Life-threatening lactic acidosis
- Anaerobic pathway and enzyme deficiency
- Intellectual disability, seizures, hypotonia
- Few survive to adolescence
- PDHA-1 (X-linked)- most often found with deficiency
Describe what occurs in anaerobic glycolysis
- Occurs in tissues where aerobic glycolysis cannot take place
- Only 2 molecules of ATP are released
Why might aerobic glycolysis not be able to occur in tissues?
- Lack of mitochondria (e.g. RBC)
- Lack of oxygen (muscle cells under extreme exertion become oxygen depleted)
Why is oxygen important in respiration?
- Terminal electron acceptor
- NADH–> NAD+ in the presence of oxygen, without it there would be a build up of NADH
- NAD+ is needed for glycolysis
- Oxidising agents unavailable without oxygen
What is the role of lactate dehydrogenase?
- Needed to convert NADH to NAD+
- Lactate pyruvate
- Allows glycolysis to continue
What is the Cori Cycle?
- Cycling of lactate produced by RBC and muscle back to glucose
How does lactate enter the liver?
- Lactate from anaerobic glycolysis diffuses into the blood where it is taken up by the liver
What happens to lactate in the liver?
- Converted back to pyruvate by lactate dehydrogenase
- Glucose released into blood to be used for energy by RBC and muscle
How much energy does the Cori Cycle consume?
- 4 net ATP per cycle
- 2 net ATP gain in anaerobic glycolysis of glucose and consumption of 6 ATP in gluconeogenesis
