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Science for Medicine A > Carbohydrates > Flashcards

Carbohydrates Flashcards

1
Q

Major carbohydrates in the diet

A

Glucose
Galactose
Fructose

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2
Q

Carbohydrates are_____

A

Highly oxidisable (H atoms)
Major source of energy
used for structural and protective functions
Cell to cell communications (receptors on RBC)

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3
Q

Stored as

A

Starch in plants

Glycogen in animals

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4
Q

Disaccharides

A

Maltose
Lactose
Sucrose

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5
Q

Glycosidic bond

A

Covalent bond between hydroxyl group (OH) and the anomeric group of another monosaccharide

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6
Q

Anomeric carbon

A

Carbon number 1

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7
Q

Features of anomeric carbon

A

Stabilises the structure of glucose

Only residue that can be oxidised

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8
Q

Maltose is____

A

a breakdown product of starch
found in beer
found in baby foods as natural sweeteners

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9
Q

Lactose is____

A

Main sugar in milk

Formed from galactose and glucose

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10
Q

Sucrose

A

Common table sugar
Only made by plants
25% of dietary carbohydrate
Sweetener is most processed food

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11
Q

Homopolysaccharides

A

single monomeric specie

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12
Q

Heteropolysaccharides

A

two or more monomer species

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13
Q

Starch contains____

A

two types of glucose polymer: amylose and amylopectin

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14
Q

Amylose

A

D glucose residues

(a1-4) linkage

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15
Q

Amylopectin

A

Branched

(a1-4) and (a1-6) every 24-30 residues

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16
Q

Amylose and amylopectin form____

A

Alpha helices

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17
Q

Glycogen

A

(a1-4) and (a1-6) every 8-12 resides- more extensively branched

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18
Q

More branched =

A

More reducing ends = more easily broken down and built up

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19
Q

Why store glucose in polymers

A

Compactness
Readily synthesised
Osmotically inactive

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20
Q

Glycoprotein

A

Class of proteins with carbohydrate covalently attached

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21
Q

Glycosaminoglycans (GAG)

A

Long unbranched polymers made from repeating units of hexuronic acid and an amino sugar

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22
Q

Proteoglycans

A

Proteins that are covalently bonded with GAGs
ECM
Part of connective tissue

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23
Q

Mucopolysaccharidoses

A

Group of disorders caused by the absence or malfunction of enzymes that are required for the breakdown of GAG

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24
Q

Example of Mucopolysaccharidoses

A

Hurler Syndrome
Dementia
Clouding of cornea
Arterial wall thickening

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25
Mouth digestion
Salivary amylase
26
Stomach digetsin
No carbohydrate digestion
27
Jejunum digestion
Isomaltase- hydrolyses (a1-6 bonds) Glucoamylase- removes glucose from non-reducing ends Sucrase- hydrolyses sucrose Lactase- hydrolyses lactose
28
Absorption of glucose
Na+ glucose symporter- driven by high extracellular Na+
29
Glucose uniporter:
GLUT2 faciltates efflux of glucose into blood
30
Fructose absorption
GLUT 5
31
Cellulose and Hemicellulose
Oligosaccharides Cannot be digested in the gut Increases faecal bulk and decreases transit time Polymers are broken down by the gut bacteria which yield CH4 and H2
32
Disaccharides deficiencies
``` Genetic Intestinal infection Inflammation of gut lining Drug injury to wall of gut Surgical removal ```
33
Lactose Intolerance
Most common disaccharidase deficiency
34
How is glucose absorbed into gut?
Diffuses through the intestinal epithelium Enters portal blood to liver Phosphorylated to Glucose-6-phosphate to trap it
35
Glucokinase
Liver High Km- High Vmax-
36
Hexokinase
Everywhere Low Km Low Vmax
37
Km
Low Km- high affinity | High Km- low affinity
38
Vmax
Low Vmax- Low rate of conversion | High Vmax- High rate of conversion
39
Glycogen
In liver when blood glucose falls converted to glucose | In skeletal muscle converted to lactate
40
What enzyme begins Glycogenesis
Glycogenin
41
Phosphoglucomutase
Glucose-6-phosphate to Glucose-1-phosphate
42
UDP-glucose phosphorylase
Catalyses the synthesis of UDP-glucose from UTP and Glucose-1-phosphate
43
Glycogen Synthase
Extends the glucose chains forming (a1-4) glycosidic bonds
44
Glycogen-branching enzymes
After a number of glucoses have been joined in a straight chain (a1-4), branching enzymes break one of the a1-4 bonds and transfers a block of residues to a more interior site in the glycogen molecule (a1-6)
45
Glycogenin
A primer than contains 8 glucosyl units and glycogen synthase extends this molecule
46
Degradation of Glycogen
Glucose monomers are removed one at a time from the non-reducing ends as G-1-P The glucose is removed then phosphorylated
47
Glucose Phosphorylase
Removed glucose from non-reducing end and phosphorylates it
48
Glucosidase
Removes final glucose
49
Hexokinase
Glucose to G-6-P
50
Glucose-6-Phosphatase
Removal of glucose from G-6-P to produce glucose
51
Phosphoglucomutase
Glucose-6-P to Glucose-1-P
52
Cori Cycle (Liver)
Lactate >> Pyruvate >>Glucose (gluconeogensis)
53
Cori cycle ( Muscle)
Glucose >>Pyruvate>>(lactate dehydrogenase)Lactate (glycolysis)
54
Key enzymes of Gluconeogenesis
1. Pyruvate Carboxylase 2. PEP Carboxykinase (PEPCK) 3. Fructose 1,6 Bisphosphatase 4. Glucose-6-Phosphatase
55
Purpose of 4 key reactions in gluconeogenesis
Bypass non-reversible reaction
56
Lactate to Pyruvate
Lactate dehydrogenase
57
Pyruvate to Oxaloacetate
Pyruvate carboxylase
58
Oxaloacetate to PEP
PEP carboxykinase
59
F-1,6 BP to F-6-P
Fructose 1,6 Bisphosphatase
60
G-6-P to glucose
Glucose-6 Phosphatase
61
Final step of Gluconeogenesis
Occurs in lumen of ER | G-6-P shuttled out of enzyme embedded in cytoplasmic membrane
62
Fructose and Galactose can__
enter glycolysis at various points
63
Pentose Phosphate Pathway
produces NADPH for all organisms
64
Starting molecule for PPP
G-6-P
65
Purpose of PPP
``` Fatty acid synthesis Steroid synthesis Antioxidant Drug metabolism Produces precursors for ATP, RNA and DNA ```
66
2 Phases of PPP
Oxidative- linear (irreversible) | Non-oxidative (reversible)
67
Non-oxidative
produces a lot of NADPH
68
Oxidative
Generates NADPH and produces pentoses
69
In liver ethanol is broken down which requires____
NAD+
70
Consequence of limited amount of NAD+
inhibits gluconeogenesis
71
Reaction A and B of gluconeogenesis require____ to convert pyruvate to PEP and Lactate to pyruvate
NAD+
72
Drinking alcohol inhibits gluconeogenesis and leads to
Increased lactate in blood and decreased blood glucose
73
G-6-P dehydrogenase
generates NADPH | Clears peroxidase from RBCs
74
G-6-P dehydrogenase deficiency
Low NADPH levels Peroxidase not cleared Oxygen forms free radicals and damages cells
75
Citric Acid Cycle
Occurs in mitochondrial matrix Indirectly produces large amounts of ATP Gateway to aerobic metabolism Removes electrons and passes it on to form NADH and FADH2
76
Citric Acid Cycle process
``` Pyruvate (PYRUVATE DEHYDROGENASE) Acetyl CoA Citrate a-ketoglutarate Succinyl CoA Oxaloacetate ```
77
Entry to cycle is controlled by_____
Pyruvate dehydrogenase- acetyl CoA and ATP negative regulate Isocitrate dehydrogenase- ATP and NADH negative regulate a-ketoglutarate dehydrogenase- ATP and NADH negative regulate

Science for Medicine A (31 decks)

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