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MEH > Carbohydrates I > Flashcards

Carbohydrates I Flashcards

1
Q

What are the Two Metabolic Pathways

A

Catabolic Pathways and Anabolic Pathways

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2
Q

What is a Catabolic Pathway

A

Break down larger molecules into smaller ones
(intermediary metabolites)
– Release large amounts of free energy
– Oxidative – release H atoms – ‘ reducing power’

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3
Q

What is an Anabolic Pathway?

A

– Synthesise larger important cellular components
from intermediary metabolites
– Use energy released from catabolism (ATP)
– Reductive (i.e. use H released in catabolism

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4
Q

Catabolism Stage 1
what is its purpose
where does it occur
what happens
is energy produced

A
  • Purpose - to convert nutrients to a form that can be taken up into cells.
  • Extracellular (GI tract)
  • Complex molecules break down to
    building block molecules
  • Short pathways
  • Breakage of C-N and C-
    O bonds (no C - C)
  • Building block molecules absorbed from the GI tract into circulation
  • No energy produced.
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5
Q

Catabolism Stage 2
what is its purpose
Are there many pathways
where does it occur
what happens
is energy produced

A
  • Purpose - Degradation of building blocks to a small number of organic precursors
  • Many pathways – not all in all tissues
  • C - C bonds broken
  • Intracellular
    (cytosolic & mitochondrial)
  • Oxidative
    (require coenzymes which are then reduced, e.g. NAD+  NADH)
  • Some energy (as ATP) produced
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6
Q

Catabolism Stage 3
what is its purpose
Are there many pathways
where does it occur
what happens
is energy produced

A

-Mitochondrial
-A single pathway – Tricarboxylic acid (TCA) cycle also know as Krebs cycle
-Oxidative (requires NAD+, FAD)
-Some energy (as ATP) is produced directly
-Acetyl (CH3CO-) converted to 2CO2
-(Also produces precursors for biosynthesis) - precursors are used for metabolic pathways aswell

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7
Q

Catabolism Stage 4
what is its purpose
where does it occur
what happens
is energy produced

A

-Mitochondrial
-Electron transport and ATP synthesis
-NADH & FAD2H re-oxidised
-O2 required (reduced to H2O)
-Large amounts of energy carrier (ATP) generated

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8
Q

In carbohydrates when can energy be produced without O2

A

Glycolysis

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9
Q

general formula for Carbohydrates

A

General formula (CH2O)n

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10
Q

What is an aldehyde

A

CHO (double bond on the O)

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11
Q

what is a KETO

A

C=O (has a double bond O but no H)

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12
Q

what is a monosaccharide

A

single sugar units, (3-9 carbons)

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13
Q

what is a Disaccharide

A

Disaccharide (2 units)

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14
Q

What is an Oligosaccharide

A

Oligosaccharide (3 –12 units) e.g. Dextrins

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15
Q

What is a Polysaccharide

A

Polysaccharide (10 – 1000’s units) glycogen, starch, cellulose

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16
Q

what are the three main dietary monosaccharides

A
  • Glucose
  • Fructose
  • Galactose
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17
Q

what are the 7 dietary carbohydrates

A
  • Glucose
  • Fructose
  • Sucrose
  • Lactose
  • Maltose
  • Starch
  • Glycogen
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18
Q

what are the three disaccharides and where do you find them

A
  • Sucrose (Table sugar. Glucose-Fructose, a disaccharide)
  • Lactose (Milk sugar. Galactose-Glucose, a disaccharide)
  • Maltose (Glucose-glucose, disaccharide)
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19
Q

what is starch

A

(Carbohydrate storage molecule in plants.
Polymer of glucose)

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20
Q

what is glycogen

A

Carbohydrate storage molecule in animals.
Polymer of Glucose
Highly Branched

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21
Q

What is the major sugar of the blood and what is the conc

A

Glucose
5 milimolars

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22
Q

What are the two reasons why some cells have an absolute requirement for glucose
Where does this occur

A
  1. Due to a lack of mitochondria, thus glycolysis is the only way to produce ATP ( RBC and lens of the eye)
  2. Due to it being in a low-oxygen environment
    Neutrophils are part of the defensive system and often find to self in a low O2 environment, they may have mitochondria but they don’t use them and also the Inner most cells of the kidney Medulla)
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23
Q

What fuel does the brain prefer
What does it use in time if starvation

A
  • CNS (brain) prefers glucose as fuel (approx. 140g/24 hours)
    (can use ketone bodies for some energy requirements in times of starvation but needs time to adapt)
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24
Q

Why isnt cellulolse (B,1-4 bonds) digested

A

Lack of the enzyme essential for breaking the beta-acetal linkages

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25
Q

cellulose (B,1-4) glycosidic bond

A

Forms linear forms of these polymers.
Well-stabilised internally from hydrogen bonding

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26
Q

alpha (1-4) Bond

A

More flexibility, allows these molecules to be packed more tightly.
Found in starch and Glycogen

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27
Q

What is primary lactase deficiency?

A

Absence of lactase persistence allele.

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28
Q

What region has the highest prevalence for primary lactase deficiency

A

The highest prevalence in Northwest Europe

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29
Q

At what age does Primary Lactase deficiency start

A

ONLY in adults,
babies have high lactase in the early months however it reduces its ability to digest by 90%

30
Q

What is Secondary Lactase deficiency

A

Secondary lactase deficiency is a shortage of lactase caused by a problem in your small intestine

31
Q

What can cause damage to the small intersitines

A
  • Esessive alchol
  • Gastroenteritis
  • Coeliac disease
  • Crohn’s disease
  • Ulcerative colitis
32
Q

Can Secondary Lactase deficiency be overcome?

A

Once epithelial cells recover, the deficiency of the secondary lactase is overcome

33
Q

At what ages does Secondary Lactase deficiency happen

A

IN BOTH BABIES AND ADULTS

34
Q

why do you get symptoms from lactose intolerance

A

When lactose isn’t digested in the small intestines it makes its way to the large intestines.
There, bacteria digest (ferment) it producing gases such as hydrogen and methane
This can change the osmotic environment causing water to be pulled into large intestines causing diarrhoea

35
Q

what is Congenital lactase deficiency

A
  • Extremely rare, autosomal recessive defect in lactase gene. Cannot digest breast milk.
36
Q

symptoms of lactose intolerance (5)

A

Symptoms:
* Bloating/cramps
* Flatulence
* Diarrhoea
* Vomiting
* Rumbling stomach

37
Q

what are the two steps in Absorption of monosaccharides

A

Active transport
Passive transport ( simple Diffusion)

38
Q

how are glucose and galactose absorbed into epithelial cells

A

Active Transport

39
Q

what does active transport require

A

Energy dependant
Sodium dependant
Carrier Protein/ Channel protein

40
Q

Absorption of monosaccharides, a summary of movement from intestines to cell.

A
  1. Active transport (low to high conc) into the intestinal epithelial cells by the sodium-dependant glucose transporter 1 (SGLT1)
  2. Passive transport (high to low conc), via GLUT 2 into the blood supply
  3. Transport via the blood supply to target tissues
  4. Glucose uptake into target cells via facilitated diffusion using transport proteins (GLUT 1- 5) ( high to low conc)
  5. GLUTS have different tissue distribution and affinities
41
Q

how does active transport work in the absorption of carbohydrates?

A

-Sodium is transported into the epithelial cell via diffusion
-Sodium takes glucose along with it from the lumen (happens via SGLT 1)
-Sodium gradient needs to be maintained therefore via active transport 3Na+ is transported out of cell in exchange for 2K+
-this process required ATP converting to ADP
(This Happens in the GLUT-2 )

42
Q

Two facts about GLUT-2 carrier protein

A

High Km
Low affinity for glucose

43
Q

How are GLUTS regulated

A

They are hormonally regulated (Insulin/glut4)

44
Q

How many different GLUTs are there

A

5

45
Q

Stage 1 Carbohydrate metabolism

A

Breakdown to building block molecules

46
Q

what is stage 2 of catabolism of carbohydrates

A

GLYCOLYSIS - (monosaccharides to pyruvate)

Break down to metabolic materials
release of ‘reducing power’
(NADH) and some ‘energy’

Intracellular, cytosolic

47
Q

Stage 3 catabolism of carbohydrates

A

TCA/ Krebs cycle
releases of reducing power
and some energy

AcetylcoA oxidised to CO2

48
Q

Stage 4 Catabolism of carbohydrates

A

Oxidative phosphorylation
Conversion of ‘reducing power’ into energy currency ATP

49
Q

What is it called when the C6 in glucose split into C3

A

Cleavage

50
Q

Does glucose get oxidisidised or reduced in glycolysis

A

There is an oxidation of glucose

51
Q

What are the Three products of glycolysis

A
  • NADH production (2 per glucose)
  • Synthesis of ATP from ADP (net= 2 ATP per glucose)
  • Provides biosynthetic precursors for FA, amino acids and nucleotides
52
Q

What are 6 Features of Glycolysis

A
  • Central pathway of CHO catabolism
  • Occurs in all tissues (cytosolic)
  • Exergonic, oxidative
  • Irreversible pathway
  • C6  2C3 (No loss of CO2)
  • With one additional enzyme (LDH), is the only pathway that can operate anaerobically
53
Q

What does HexoKinase (glucokinase in liver) do?

A

The enzyme responsible for the Change of glucose to Glucose 6-P using ATP
(the phosphorylation of glucose)

54
Q

What does Phosphofructokinase -1 do?

A

Phosphofructokinase is an enzyme that controls glycolysis in the body, which is in turn a metabolic pathway necessary for converting glucose into pyruvate

55
Q

Phase 1 of glycolysis, Reaction 1-3

A
  • Phosphorylation of glucose to glucose-6- phosphate
    (G-6-P)
    -Makes glucose negatively charged (anionic)
    -Prevents passage back across the plasma membrane
  • Increases the reactivity of glucose to permit subsequent steps
  • Phase 1 USES 2 moles ATP per mole glucose
  • Reaction 1 and 3 have large negative ∆G values, so are irreversible
  • Step 3 - Committing step: first step that commits glucose to metabolism via glycolysis
56
Q

Phase 2 of glycolysis reaction(4-10)

A

Reaction 4
* Cleavage of C6 into two C3 units * C3 units interconvertible
(reaction 5)
Reaction 6
* Small amount of reducing power captured (2x NADH)
Reactions 7 and 10 – 4x ATP synthesis
* Transfer Pi to ADP to give ATP * ‘Substrate level
phosphorylation’
Reaction 10
* Large -ve ∆G (exothermic), therefore irreversible

57
Q

Why are there so many steps (enzymes) in Glycolysis
(4)

A

Why so many steps/enzymes?
1. Chemistry is easier in small stages
2. Efficient energy conservation
3. Gives versatility
* allows interconnections with other pathways
* allows production of useful intermediates
* allows a part to be used in reverse
4. Allows for fine control

58
Q

How many enzymes, coenzymes and intermediates are involved in glycolysis

A

10 enzymes, 5 coenzymes, 9 intermediates

59
Q

What does the Phosphorylation of glucose to glucose-6- phosphate (G-6-P) do to the glucose

A
  • Makes glucose negatively charged (anionic)
  • Prevents passage back across the plasma membrane
  • Increases the reactivity of glucose to permit subsequent steps
60
Q

How much ATP does phase 1 of glycolysis use

A

Phase 1 USES 2 moles ATP per mole of glucose

61
Q

Which steps in phase 1 are irreversible for glycolysis and why ?

A

Reaction 1 and 3 have large negative ∆G values, so are irreversible

62
Q

What is the committing step in phase 1 glycolysis?

A

Step 3 - Committing step: first step that commits glucose to metabolism via glycolysis

63
Q

what happens in reaction 4
of Phase 2 of Glycolysis

A

Reaction 4
* Cleavage of C6 into two C3 units
* C3 units interconvertible

64
Q

what happens in reaction 6
of Phase 2 of Glycolysis

A

Reaction 6
* Small amount of reducing power captured (2x NADH)
(NAD+ becomes NADH)

65
Q

What happens from reactions 7- 10 in glycolysis

A

4x ATP synthesis (produced)
* Transfer Pi to ADP to give ATP
* ‘Substrate level
phosphorylation’

66
Q

What happens in reaction 10 of glycolysis

A

Reaction 10
* Large -ve ∆G (exothermic), therefore irreversible

67
Q

IMPORTANT INTERMEITIATES from glycolysis

A

Fats, Triglycerides
Amino acids - protein sytheisi
Sugars
Heam

68
Q

Why is lactic acid important in the production of anaerobic glycolysis

A

When the body has plenty of oxygen, pyruvate is shuttled to an aerobic pathway to be further broken down for more energy. But when oxygen is limited, the body temporarily converts pyruvate into a substance called lactate, which allows glucose breakdown—and thus energy production

69
Q

Explain how the blood concentraion of lactate is controlled

A

Lactate can only be metabolized by the conversion to pyruvate. Therefore, blood lactate levels depend on pyruvate metabolism.

70
Q

Explain the biochemical basis of the clinical conditions of galactosamia

A

In Galactosaemia, increased activity of the enzyme aldose reductase consumes excess NADPH and in the case of G6PDH deficiency, the production of NADPH is limited (G6PDH is the first enzyme in the pentose phosphate pathway). Insufficient levels of NADPH limit the ability to recycle oxidised glutathione (GSSG) back to its protective reduced form (GSH) leaving the cell susceptible to oxidative damage.

71
Q

Explain why the pentose phosphate pathway is an important metabolic pathway in some tissues.

A
  • Starts from Glucose-6-Phosphate
  • an important source of NADPH
    • reducing power for biosynthesis
    • maintains GSH levels
    • detoxification reactions
      Makes C5 sugar ribose used in
    • Nucleotides
    • DNA and RNA
    • No ATP made — CO2 made
72
Q

Describe the clinical condition of glucose 6-phosphate dehydrogenase deficiency and explain the biochemical basis of the signs and symptoms.

A

This enzyme helps red blood cells work properly.
A lack of this enzyme can cause hemolytic anaemia. This is when the red blood cells break down faster than they are made.

Symptoms during a hemolytic episode may include dark urine, fatigue, paleness, rapid heart rate, shortness of breath, and yellowing of the skin (jaundice).

MEH (13 decks)

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