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foundations of medicine > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

What are is the function of carbohydrates

A

Highly oxidizable - major metabolic process
Store potential energy - glycogen
Structural/protective - ECM of cells
Contribute to cell-to-cell communication - ABO blood groups

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2
Q

What are monosaccharides

A

Carb with one sugar subunit
3 hexoses (6C sugars) - Glucose (Glc), Galactose (Gal), Fructose (Fru)

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3
Q

What are disaccharides

A

Monosaccharide monomers, linked by glycosidic bond
3 important - Maltose, Lactose, Sucrose

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4
Q

What is a glycosidic bond

A

Covalent bond between hydroxyl group and anomeric carbon

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5
Q

What is an anomeric carbon

A

Different anommers are mirros images
C 1 on Glc residue
Stabilises Glc structure
Only residue that can be oxidised

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6
Q

Describe maltose

A

Anomeric C-1 can be oxidised
Reducung sugar

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7
Q

Describe Lactose

A

Glycosidic bond between galactose and glucose
Anomeric C on glucose is oxidised, reducing sugar

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8
Q

Describe Sucrose

A

No free anomeric C-1
no oxidiation site
non-reducing sugar

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9
Q

Descibre Polysaccharides

A

Long chain carbs, many monosaccharide monomers

Homopolysaccharides - single monomeric species
Heteropolysaccharides - Two or more monomeric species

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10
Q

Descibe Starch

A

Two types of Glc polymers:
Amylose (20-25%) - (α1→4) join glucose chains
Amylopectin (75-80%) - (α1→6) create branches

Many non-reducing ends, few reducing

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11
Q

Describe Oligosaccharides

A

Polymer with small numbers of monsaccharides
Cell regeneration and cell adhesion
Lack in diet lead to poor health

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12
Q

Describe the digestion of Carbs

A

Mouth - Salivary amylase hydrolyses (α1→4) bonds of starch
Stomach - no carb digestion
Small intestines

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13
Q

Describe the digestion of carbs in small intestines

A

Isomaltase - hydrolyses (α1→6) bonds
Glucoamylase – removes Glc sequentially from non-reducing ends
Sucrase – hydrolyses sucrose
Lactase – hydrolyses lactose

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14
Q

Describe the absorbtion of glucose

A
  1. Absorbed indirectly by ATP into epithelial cells
  2. Glucose and Na+ transported at same time down Na+ conc. gradient
  3. Works continually even when blood glucose is high
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15
Q

Describe the absorbtion of Galactose

A

Similar to glucose, using conc. gradients to facilitate transport

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16
Q

Describe the absorbtion of Fructose

A

Binds to channel protein GLUT5
Moves down conc. gradient, high in gut lumen low in blood

17
Q

Fate of absorbed glucose

A

Absorbed by intesine epithelial cells into blood towards liver
Phosphorolated to glucose-6-phosphate by hepatocytes
G6P cannot diffuse out cell

18
Q

What enzymes catalysts are there for glucose absorbtion

A

Glucokinase (liver)
Hexokinase (other tissues)

19
Q

Describe Glucokinase

A

Blood Glc is high
High glucokinase Vmax can phosphorylate Glc quickly
Most absorbed Glc trapped in liver

20
Q

Describe hexokinase

A

Hexokinase low Km means at low Glc, tissues can absorb effectively
Hexokinase low Vmax, tissues “easily satisfied”, don’t keep absorbing Glc

21
Q

What is the function of glycogen

A

Energy storage
90% in:
Liver - replenishes blood glucose when fasting
Skeletal muscle - catabolism produces ATP for contraction

22
Q

Describe glycogen synthesis

A

Step 1:

  1. Glygogenin (enz) covalently bonds Glc from (UDP)-glucose to chains of 8 Glc
  2. Glycogen synthase extends Glc chains

Step 2:

  1. Glycogen chains broken by glycogen-branching enzyme and re-attached by (α1→6) bonds to give branch points
23
Q

What is the process of glycolysis

A

1 - Phosphorylation of Glc - hexokinase, 1 ATP used
2 - G-6-P to F-6-P
3 - F-6-P to F-1,6-bisP
6 - Oxidation of Glyceraldehyde-3-P to 1,3-bisPGlycerate - 2 NADH produced
7 - Pi transfer from 1,3-bisPG to ADP = 3-PG, 2 ATP produced
10 - Transfer of Pi from PEP to ADP = Pyruvate, 2 ATP produced

24
Q

What happens to pyruvate

A
  1. Ethanol
  2. Lactate
  3. CO2
25
Q

Describe pyruvate to lactate

A

NADH oxidation reduces pyruvate to lactate
Nad+ replinished for glycolysis
Lactate dehydrogenase is catalyst
Redox balanced

26
Q

Describe pyruvate to acetyl coenzyme A (acetyl CoA)

A

Cells with access to O2, pyruvate oxidised to acetyl CoA
Pyruvate dehydrogenase acts as catalyst

27
Q

What is the precursor to gluconeogenesis

A

Lactate (non-carbs), get turned into glucose

28
Q

What is the function and process of gluconeogenesis

A

4 reactions that sidestep 3 irreversible reactions of glycolysis (1,3,10)
Independent control of glycolysis and gluconeogenesis pathways

29
Q

What are the 4 bypass reactions

A

A - Pyruvate to Oxaloacetate
B - Oxaloacetate to PEP
C - Fru 1,6 Bisphos to F-6-P (step 3)
D - G-6-P to glucose (step 1)

30
Q

What are the fates of absorbed fructose and galactose

A

Fructose and galactose can enter glycolysis at various points

31
Q

What is substrate level phosphorylation

A

Phosphate group is transferred from donor compound
Method of ATP production

32
Q

What is Oxidative phosphorylation

A

Metabolic pathway generates ATP from ADP
Oxidation of nutrients gives energy for phosphorylation

33
Q

What is the cori cycle

A

Lactate to Glucose in liver
Glucose to Lactate in Muscle

34
Q

What is function of galactokinase

A

Phosphorylate galactose with ATP to galactose-1-phosphate

35
Q

What is fructokinase

A

Catalyzes conversion of fructose and ATP into fructose-1-phosphate and ADP

36
Q

What is a glycoprotein

A

Proteins with carbs covalently attached

Increases proteins solubility
Influence protein folding and conformation
Protect from degradation
Communicate between cells

37
Q

What is a proteoglycan

A

GAGs covalently attaching to proteins
Macromolecules found on surface of cells or ECM
Form part of many connective tissues in body

foundations of medicine (28 decks)

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