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ZA - Science for Medicine > Carbohydrates > Flashcards

Carbohydrates Flashcards

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1
Q

What are the main monosaccharides and why are they called hexoses?

A

Glucose
Galactose

Made of 6C

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2
Q

What are the main disaccharides?

A

Maltose
Lactose
Sucrose

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3
Q

What bond joins together sugar monomers?

A

Glycosidic

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4
Q

What do glycosidic bonds form between?

A

An OH group of one monomer and the anomeric carbon of another

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5
Q

Why are maltose and lactose classed as reducing sugars?

A

They have a free anomeric carbon 1 which can be oxidised

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6
Q

Why is sucrose not a reducing sugar?

A

Has no free anomeric carbon 1

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7
Q

What are the two types of polysaccharides?

A

Hetero and Homo

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8
Q

What is a heteropolysaccharide?

A

A polysaccharide made from two or more monomer species

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9
Q

What is a homopolysaccharide?

A

Polysaccharide made from one monomer species

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10
Q

Example of a polysaccharide?

A

Starch or Glycogen

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11
Q

What makes up starch?

A

Two glucose polymers - amylose and amyopectin

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12
Q

Difference between amylose and amylopectin?

A

Amylose is not branched and had alpha1–>4 bonds

Amylopectin is branched and has alpha1–>4 and alpha1–>6 bonds.

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13
Q

Is glycogen more or less branched than starch?

A

More

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14
Q

Why would we store glucose as glycogen?

A

Compactness

Glycogen has many reducing ends making it easily utilised to form glucose

Glycogen is not osmotically active yet glucose is - easier to keep glycogen in a cell than it is glucose.

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15
Q

Why is glycogen osmotically inactive?

A

Polymers form hydrated gels

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16
Q

Proteins with a carbohydrate attached are called?

A

Glycoproteins

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17
Q

Benefits of a glycoprotein?

A

Increased solubility

Influences conformation and folding

Protects it from degradation

Acts as a cell to cell communicator

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18
Q

Where are the 3 locations of carb digestion?

A

Mouth
Duodenum
Jujunum

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19
Q

What happens in mouth?

A

Salivary amylase breaks down alpha1–>4 bonds

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20
Q

What happens in the duodenum?

A

Pancreatic amylase acts same as in mouth

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21
Q

What happens in the jujunum?

A

Final digestion by 4 enzymes;

Isomaltase - breaks down alpha1–>6 bonds

Glucoamylase - removes glucose from non reducing ends of carb

Sucrase and Lactase - hydrolyses their sugars

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22
Q

What is the end product of carb digestion?

A

Glucose, Galactose and Fructose

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23
Q

How is glucose absorbed after digestion?

A

It binds to Sodium and enters the cell against its own gradient but along sodiums gradient.

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24
Q

How does galactose get absorbed?

A

Similar to glucose

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25
Q

How is fructose absorbed?

A

Binds to GLUT5 channel protein and moves down its concentration gradient

26
Q

What breaks down cellulose and hemicellulose?

A

Not us, gut bacteria do releasing CH4 anf H2 gas

27
Q

Example of a disaccharide deficiency?

A

Lactose intolerance

28
Q

Explain lactose intolerance?

A

Lactase is deficient

Lactose not digested - osmotically active brings water into gut causing diarrhoea

Lactose broken down by gut bacteria - gas build up and irritant acids

29
Q

Function of hexokinase and glucokinase ?

A

To phosphorylate glucose to G-6-P

30
Q

Hexokinase and glucokinase are isoenzymes, what does this mean?

A

They have the same function, yet different structure, Vmax and Km

31
Q

What is glucokinase for?

A

Has a high Km and a High Vmax, allowing to to grab lots of glucose fast and trap it quickly, only working when there is a high concentration of glucose due to high Km.

Found in hepatocytes

32
Q

What is hexokinase used for?

A

Used in tissues - has a low Km meaning it can grab glucose more effectivly at low conc.

Has a Low Vmax meaning tissues won’t over grab and phosphorylate glucose

33
Q

What is G-6-P used for?

A

Can be turned back to glucose and used, sent to make pentoses or stored as glycogen

34
Q

How is glycogen synthesised?

A

Glycogenin covalently bonds glucose to UDP forming chains 8 residues long.

Glycogen synthase then takes over and extends the glucose chains.

Glycogen branching enzyme then breaks the chain and reattaches it as branches via alpha1–>6 bonds.

35
Q

How is glycogen degraded?

A
  1. Glucose monomers are removed one at a time as G-1-P from non reducing ends. Phosphorylated by glycogen phosphorylase.
  2. Remaining glycogen moecules is debrached by the transferase activity of a de-branchin enzyme which removes 3 of the last 4 glucose residues on a branch and reattaches it to the nearest non-reducing of main chain via alpha1–> 4 bonds.
  3. Last branched glucose is removed by glucosiadase leaving behind an unbranched glycogen chain which glycogen phosphorylase can act upon as needed.
36
Q

What is glycolysis?

A

A catbolic pathway that forms ATP and pyruvate from glucose anerobically via substrate-level phosphorylation.

Occurs in cytosol so no complex organelles needed.

37
Q

How many phases does glycolysis have?

A

2 - preparatory and payoff phases each with 5 steps.

38
Q

How many ATP are used and made in glycolysis?

A

Per glucose;

2 ATP needed for preparatory phase

4 made in payoff phase

39
Q

Why is glycolysis not reversible?

A

It has overall -ve change in gibbs free energy making it spontaneous. It has 3 very spontanous steps which make this irreversible

40
Q

What happens at the end of the prep phase?

A

Glucose makes G-3-P

Step 3 of this phase is irreversable and first commited phase.

41
Q

What happens end of payoff phase?

A

2 G-3-P molecules end up as 2 ATP and 2 NADH

42
Q

Why does NAD+ need to be regenerated?

A

For use in metabolic pathways to reduce various intermediate metabolites

43
Q

Example of NAD+ regeneration?

A

During anerboic respiration, Pyruvate changed to lactate using NADH–>NAD+ which can go off and be used as needed.

44
Q

What is the use and regeneration of NAD+ termed as?

A

Redox balance

45
Q

How is pyruvate converted to lactate?

A

Via fermentation - is reduced to lactate using lactate dehydrogenase and is driven by oxidation of NADH to NAD+ - redox balance.

46
Q

How is lactase later changed to glucose?

A

In the liver via gluconeogenisis.

47
Q

What is the cori cycle?

A

Interaction between the liver and muscles

48
Q

How is pyruvate converted to acetyl CoA?

A

Aerobic respiration - pyruvate is moved to the mitochondria and enzyme pyruvate dehydrogenase turns it to Acetyl-CoA and CO2. This also involves the reduction of NAD+ to NADH

49
Q

What is gluconeogenisis?

A

Process of making glucose from non carb molecules when body is starving/fasting

50
Q

Since glycolysis is irreversible, how does gluconeogenisis occur?

A

Uses bypass reactions to get passed the 3 irreversible steps

51
Q

What are bypass reactions A and B?

A

Occur in mitochondria - Lactate to pyruvtae via lactatse dehydrogenase and NADH to NAD+.

Pyruvate undergoes reaction A - pyruvate to oxaloacetate.

Reaction B - oxaloactetae to PEP.

52
Q

Reaction C?

A

F-1,6-bisP to F-6-P

53
Q

Reaction D?

A

Final step in gluconeogenisis

G-6-P to Glucose

54
Q

What is the fate of fructose?

A

Joins glycolysis using ATP to form F-1-P and then glyceraldehyde and using 1 more ATP forming glyceraldehyde-3-phosphate.

55
Q

Fate of galactose?

A

Joins glycolysis through conversion of glucose-1-phosphate by UDP.

56
Q

What does the pentose phosphate pathway do?

A

Produces NADPH and pentose sugars

Also metabolises pentose sugars in diet

57
Q

What are pentose sugars needed for?

A

Nucleic acid synthsis

58
Q

2 phases of pentose phosphate cycle?

A

Oxidative irreversible -
G-P-6 to pentose phosphate
AND
Makes NADPH

Non oxidative reversible - Interconverts G-P-6 and pentose phosphate to form lots of 3 to 7 carbon sugars

59
Q

Difference between NAD+ and NADP+?

A

NAD+ - used in metabolism

NADP+ - used in anabolism

60
Q

What does alcohol inhibit in liver which slows gluconeogenisis?

A

NAD+ is used to break ethanol down, not enough for gluconeogenisis.

ZA - Science for Medicine (19 decks)

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