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
Describe pyruvate to lactate
NADH oxidation reduces pyruvate to lactate Nad+ replinished for glycolysis Lactate dehydrogenase is catalyst Redox balanced
26
Describe pyruvate to acetyl coenzyme A (acetyl CoA)
Cells with access to O2, pyruvate oxidised to acetyl CoA Pyruvate dehydrogenase acts as catalyst
27
What is the precursor to gluconeogenesis
Lactate (non-carbs), get turned into glucose
28
What is the function and process of gluconeogenesis
4 reactions that sidestep 3 irreversible reactions of glycolysis (1,3,10) Independent control of glycolysis and gluconeogenesis pathways
29
What are the 4 bypass reactions
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
What are the fates of absorbed fructose and galactose
Fructose and galactose can enter glycolysis at various points
31
What is substrate level phosphorylation
Phosphate group is transferred from donor compound Method of ATP production
32
What is Oxidative phosphorylation
Metabolic pathway generates ATP from ADP Oxidation of nutrients gives energy for phosphorylation
33
What is the cori cycle
Lactate to Glucose in liver Glucose to Lactate in Muscle
34
What is function of galactokinase
Phosphorylate galactose with ATP to galactose-1-phosphate
35
What is fructokinase
Catalyzes conversion of fructose and ATP into fructose-1-phosphate and ADP
36
What is a glycoprotein
Proteins with carbs covalently attached Increases proteins solubility Influence protein folding and conformation Protect from degradation Communicate between cells
37
What is a proteoglycan
GAGs covalently attaching to proteins Macromolecules found on surface of cells or ECM Form part of many connective tissues in body