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Metabolism > Carbohydrates- Glycolysis > Flashcards

Carbohydrates- Glycolysis Flashcards

1
Q

What are the dietary forms of carbohydrates?

A

Starch, sucrose, lactose fructose and glucose

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2
Q

What hormone is released after eating?

A

Insulin

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3
Q

What does insulin do?

A
  • Stimulates the formation of glycogen from glucose

- Involved in glucose storage and immediate use of glucose after eating

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4
Q

When is glucagon released?

A
  • A while after eating, when glucose levels have dropped in the blood
  • Stimulates breakdown of glycogen into glucose
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5
Q

What type of receptor is the insulin receptor on cells?

A

Tyrosine Kinase Receptor

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6
Q

What do Ras/kinase pathways do?

A

Control gene expression involved in glucose metabolism

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7
Q

What are the glucose transporters?

A
  • Family of transporters

- GLUT-1 to 4

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8
Q

What is the role of each GLUT transporter?

A
  • 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
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9
Q

What is a sodium dependent glucose transporter (SGLT) and how is it different?

A
  • 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
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10
Q

What happens to excess carbohydrates in the fed state?

A
  • Taken up by liver and converted into fats
  • Packaged into vesicles and stored in adipose tissue
  • Occurs when you eat beyond energy requirements
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11
Q

What happens to glucose in the fed state?

A
  • Transported to the liver and brain
  • Converted to Acetyl CoA and entered into TCA cycle
  • Red blood cell consistently takes up glucose
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12
Q

What happens to glucose in red blood cells in the fed state?

A
  • Has no mitochondria
  • Glucose does not enter TCA cycle
  • Produces some localised ATP through anaerobic respiration
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13
Q

What happens to glucose in muscles in the fed state?

A
  • Generate a glycogen reserve for themselves

- Stores glycogen for future immediate use

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14
Q

When does the basal state occur?

A
  • A short while after eating

- Glucose levels in the blood would have diminished by the point

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15
Q

Where does excess glucose go in the basal state?

A
  • Adipose tissue and muscles

- Similar to fed state

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16
Q

Describe and explain the levels of insulin and glucagon in the basal state

A
  • Insulin decreased

- Glucagon increased in order to draw glucose from glycogen stored

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17
Q

What happens in the liver in the basal state?

A
  • Glycogen reserves are used to maintain blood sugar levels

- Maintenance and prevention of hypoglycaemia

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18
Q

What happens in the brain in the basal state?

A
  • Uses glucose from the blood
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19
Q

What happens in red blood cells in the basal state?

A
  • Converts glucose to lactate
  • Lactate goes back to the liver and converts back to glucose
  • Lactate cycels
20
Q

What happens in adipose tissue in the basal state?

A
  • 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
21
Q

What happens in adipose tissue in the prolonged fast state?

A
  • No glycogen left so adipose must be used

- Glycerol is used as raw material

22
Q

What happens to muscle protein in the prolonged fast state?

A
  • Can be used as fuel for glucose and access of other amino acids
  • Does not tend to compromise overall health unless used excessively
23
Q

What happens in the brain in the prolonged fast state?

A
  • Relinquishes its need for glucose and requires ketone bodies instead
  • Preference for glucose diminishes as red blood cells need it more
24
Q

What molecule are glucose, amino acids and fatty acids converted to for respiration?

A

Acetyl CoA

25
Q

What is the importance of Acetyl CoA in respiration?

A
  • 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
26
Q

Describe glycolysis

A
  • Splitting of glucose
  • First stage of glucose oxidation
  • Can happen aerobically/anaerobically
27
Q

What type of respiration do red blood cells undergo?

A

Anaerobic respiration

28
Q

What are oxidation and reduction?

A
  • Oxidation- loss of electrons/hydrogen

- Reduction- gain of electrons or hydrogen

29
Q

What is NAD?

A
  • Nicotinamide Adenine Dinucleotide
  • Co-enzyme found in all living cells
  • Contains 2 nucleotide- one with adenosine ring and one with nicotinamide
30
Q

What is the role of NAD+ in metabolism?

A
  • Involved in redox reactions

- Carrying electrons from one reaction to another

31
Q

Describe NAD+ as an oxidising agent

A
  • Accepts electrons from other molecules

- Becomes reduced- this reactions forms NADH

32
Q

Describe NADH as a reducing agent

A
  • Donates electrons to electron transport chain

- Forms NAD+

33
Q

What does aerobic glycolysis require?

A
  • Mitochondria

- Presence of oxygen

34
Q

How much ATP is produced from aerobic respiration?

A
  • Plentiful supply- around 36 moles

- Preferential way

35
Q

Describe the first step in aerobic glycolysis

A
  • Glucose-> Glucose-6-phosphate-> fructose-6-phosphate

- This reaction uses one molecule of ATP

36
Q

Describe the second step in aerobic glycolysis

A
  • Fructose-6-phosphate-> fructose-1,6-bisphosphate

- This reaction uses on molecule of ATP

37
Q

Describe the third step in aerobic glycolysis

A
  • 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
38
Q

Describe what happens in the link reaction between glycolysis and TCA cycle

A
  • Pyruvate to Acetyl CoA
  • Uses enzyme pyruvate dehydrogenase
  • Also NAD–> NADH
39
Q

What are the consequences of pyruvate dehydrogenase deficiency?

A
  • 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
40
Q

Describe what occurs in anaerobic glycolysis

A
  • Occurs in tissues where aerobic glycolysis cannot take place
  • Only 2 molecules of ATP are released
41
Q

Why might aerobic glycolysis not be able to occur in tissues?

A
  • Lack of mitochondria (e.g. RBC)

- Lack of oxygen (muscle cells under extreme exertion become oxygen depleted)

42
Q

Why is oxygen important in respiration?

A
  • 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
43
Q

What is the role of lactate dehydrogenase?

A
  • Needed to convert NADH to NAD+
  • Lactate pyruvate
  • Allows glycolysis to continue
44
Q

What is the Cori Cycle?

A
  • Cycling of lactate produced by RBC and muscle back to glucose
45
Q

How does lactate enter the liver?

A
  • Lactate from anaerobic glycolysis diffuses into the blood where it is taken up by the liver
46
Q

What happens to lactate in the liver?

A
  • Converted back to pyruvate by lactate dehydrogenase

- Glucose released into blood to be used for energy by RBC and muscle

47
Q

How much energy does the Cori Cycle consume?

A
  • 4 net ATP per cycle

- 2 net ATP gain in anaerobic glycolysis of glucose and consumption of 6 ATP in gluconeogenesis

Metabolism (9 decks)

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