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SFM (Scientific Foundations of Medicine) > Lecture 3: Carbohydrate Metabolism > Flashcards

Lecture 3: Carbohydrate Metabolism Flashcards

1
Q

What are GLUTs?

A

Glucose transporters that bring glucose into cells

GLUT 1 –> RBCs/Brain
GLUT 2 –> Liver (LOW AFFINITY)
GLUT 3 –> Neurons
GLUT 4 –> Cardiac, Skeletal, Adipose cells
- INSULIN DEPENDENT (Upregulates expression)

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2
Q

What are the 3 phases of Glycolysis?

A

Phase 1: Investment –> use 2 ATP
Phase 2: Splitting –> one 6C into two 3C
Phase 3: Payoff –> generate 4 ATP

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3
Q

Phase 1 Enzymes: Hexokinase, Glucokinase, Phosphofructokinase-1

A

Hexokinase (all cells)
(-) - G6P

Glucokinase (liver, pancreatic B cells)
(+) - glucose, F1P, insulin
(-) - glucagon, F6P

Phosphofructokinase-1 RATE LIMITING STEP (Glycolysis)
(+) - AMP, F2,6BP
(-) - ATP, Citrate

F2,6BP formed via PFK-2/FBPase-2 (bifunctional)

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4
Q

Phase 2 Enzymes: Aldolase, triose phosphate isomerase

A

Aldolase –> 6C into 2x 3C (DHAP/G3P)

Triose Phosphate Isomerase –> make 2 G3P
- DHAP into G3P

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5
Q

Phase 3 Enzyme: Pyruvate Kinase

A

Pyruvate Kinase - gen. 2 pyruvate molecules from PEP
(+) - insulin, F1,6BP
(-) - alanine, ATP, glucagon (PEP enter gluconeogenesis)

IRREVERSIBLE

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6
Q

What is Tarui Disease (biochemical)?

A
  • deficiency in PFK-1 (GSD VII)

- exercise-induced muscle cramps and weakness

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7
Q

Where does Glucose-6-Phosphate get utilized other than Glycolysis?

A

Pentose Phosphate Pathway

  • used to make Ribose and NADPH
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8
Q

Effects of Glycolysis deficiency on Red Blood Cells

A
  • lack mitochondria, glycolysis only means to gen. ATP
  • no glycolysis –> ATP deficiency (ion gradient ruined)
  • dec. cell viability, RBC destruction = hemolytic anemia
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9
Q

What is Diabetes and what are some of the problems caused by it?

A
  • disease characterized by hyperglycemia

Type 1: insulin deficiency (Pancreatic B cells lost)
Type 2: insulin resistance (loss of B cells functions)

causes: mutations (GK, mito tRNA genes), aberrant proinsulin –> mature insulin conversion, defective receptors
symptoms: elevated BGL, polydipsia, polyuria, unexplained weight loss

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10
Q

Fasting blood glucose lvls (prediabetic and diabetic)

A

prediabetic - 100-125 mg/dL

diabetic > 125 mg/dL

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11
Q

Hemolytic Anemia and its clinical markers

A
  • caused by premature destruction of RBCs

clinical markers: elevated lactate dehydrogenase (LDH), unconjugated bilirubin

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12
Q

Fanconi-Bickel Syndrome

A
  • autosomal recessive
  • mutation in GLUT 2 transporter
  • unable to take up glucose, fructose, galactose
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13
Q

What are the 4 regulatory enzymes of Gluconeogenesis?

A
  1. Pyruvate Carboxylase (BIOTIN cofactor)
    (+) - acetyl CoA, cortisol
    (-) - ADP
  2. PEP Carboxykinase (PEP CK)
    (+) - cortisol, glucagon, thyroxine
  3. Fructose 1,6, Biphosphatase (RATE LIMITING STEP)
    (+) - citrate, cortisol
    (-) - AMP, F2,6BP
  4. Glucose-6-Phosphatase
    (+) - cortisol
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14
Q

Precursors of Gluconeogenesis and where they enter at (G6P, G3P, DHAP, Oxaloacetate)

A
  1. G6P –> galactose, glycogen
  2. G3P –> fructose
  3. DHAP –> glycerol, frucose
  4. OAA –> propionate, glucogenic AA
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15
Q

Fructose 1,6 Biphosphatase Deficiency

A
  • similar to Tarui disease in Glycolysis
  • rate limiting step disorder
  • present in infancy/early childhood
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16
Q

Von Gierke disease (GSD Ia)

A

deficiency in glucose-6-phosphatase

  • inefficient release of free glucose into bloodstream in liver
17
Q

What do GLUT5, GLUT2, and SGLT1 transport?

A

GLUT5 –> fructose

GLUT2 –> glucose, galactose, fructose

SGLT1 –> fructose, galactose, sodium

18
Q

Polyol Pathway (Sorbitol) and problem

A

glucose –> sorbitol (aldose reductase)
sorbitol –> fructose (sorbitol dehydrogenase)

no sorbitol dehydrogenase = sorbitol buildup
- water influx, swelling –> retinopathy, cataracts, peripheral neuropathy

19
Q

What is the rate limiting step of galactose metabolism?

A

GALT

glucose 1P uridyltransferase

20
Q

Fructose Metabolism and excessive consumption

A
  • much faster than glucose metabolism
  • bypasses rate limiting step of glycolysis (no PFK-1)
    • G3P/DHAP from unregulated synthesis
  • excess ACoA –> FA, transported to adipocytes –> TAGS (obesity)
  • liver accumulates FA (fatty liver)
21
Q

Lactose Intolerance

A
  • cannot metabolize lactose (milk = GI disturbances)

- deficiency in lactase (break down lactase into glucose/galactose)

22
Q

Galactosemia (GALT and Galactokinase)

A
  1. GALT deficiency –> galactitol accumulation
    • classic galactosemia: liver failure, sepsis, bleeding
  2. Galactokinase deficiency
    • nonclassical type: galactose/galactitol in blood/urine
    • galactitol (eye) –> cataracts (early infancy)
23
Q

Cataracts

A
  • clouding of normally clear lens of eye

- transferase not active, aldolase reductase converts galactose to galactitol

24
Q

Pentose Phosphate Pathway

A
  • no NRG production, produces NADPH and sugars for RNA/DNA formation
  • in cytosol; oxidation G6P to ribulose 5-P
  • irreversible oxidative step and reversible non-oxidative step
25
Q

Oxidative Phase PPP and G6P dehydrogenase

A

G6PD –> RATE LIMITING ENZYME (NADP –> NADPH)

  • NADPH regenerates glutathione (antioxidant)
  • G6PD deficiency –> hemolytic anemia
26
Q

Nonoxidative Phase PPP and transketolase/transaldolase

A
  • regenerative phase (reversible)
  • end products go to glycolytic, gluconeogenic, nucleotide synthesis pathways

transketolase: TTP required, transfer of 2C
transaldolase: transfer of 3C

27
Q

Glycogen Structure

A
  • long homopolymer of glucose molecules

a-1,4 glycosidic bonds (long chain bonds)
a-1,6 glycosidi bonds (branch points)

reducing end: glucose monomer w/glycogenin
non reducing end: where degraded/extended from

glycogenin –> serves as primer for glycogen synthesis

28
Q

Glycogen Storage and Functions

A
  • stored in liver, muscles as granules

granules also contain enzymes needed for metabolism

liver function: BGL regulation
muscle function: reservoir of fuel for activity

29
Q

Glycogenesis Enzymes (Trapping Glucose)

A
  1. hexokinase/glucokinase
  2. phosphoglucomutase (PGM)
    • G6P –> G1P
  3. UDP-glucose pyrophosphophorylase
    • G1p –> UDP-glucose (active form)
30
Q

Glycogenesis Enzymes (elongation and branching)

A

Elongation: Glycogen Synthase (RATE LIMITING STEP)

  • glucose (UDP-glucose) added to glycogen primer
  • a-1,4 glycosidic bond

Branching: glucosyl (4:6) transferase

  • chain is 11 long, 7 break off to make branch
  • a-1,6 glycosidic bond
  • increases solubility of glycogen
31
Q

Glycogenolysis Enzymes (shortening and release)

A

Shortening: Glycogen Phosphorylase (RATE LIMIT STEP)

  • uses B6 as cofactor
  • removes glucose until gets to 4 residues

Release: debranching enzyme

  • transfer 3 of 4 glucose to non-reducing end
  • cleaves a-1,6 glycosidic bond to release glucose
32
Q

Normal, Prediabetic, Diabetes mellitus fasting and fed glucose levels

A

Normal

  • Fasting: 70-100 mg/dL
  • Fed: =/< 140 mg/dL

Prediabetic

  • Fasting: 100-125 mg/dL
  • Fed: > 140 mg/dL

Diabetes Mellitus

  • Fasting: =/> 126 mg/dL
  • Fed: =/> 199 mg/dL
33
Q

GSD 0

A
  • deficiency in glycogen synthase
  • cannot synthesize/store glycogen
  • muscle cramps, need to eat frequently
34
Q

GSD1a

A
  • Von Gierke disease
  • deficiency in glucose 6-phosphatase
  • cannot release free glucose into blood stream (liver)
35
Q

GSD II

A
  • Pompe disease
  • deficiency in Acid Maltase (acid a-glucosidase)
  • impairs lysosomal glycogenolysis (glycogen accumulation in lysosomes
  • progressive muscle weakness (myopathy)
36
Q

GSD III

A
  • Cori Disease
  • deficiency in a-1,6 glucosidase (debranching enzyme)
  • glycogen w/LARGE # short branches
  • light hypoglycemia and hepatomegaly
37
Q

GSD IV

A

Andersen Disease

  • deficiency in glucosyl (4:6) transferase (branching enzyme)
  • long chain glycogen w/fewer branches
  • spleen/liver enlargement, tissue scarring (cirrhosis)
38
Q

GSD V

A

McArdle Disease

  • deficiency in muscle glycogen phosphorylase
  • unable to supply muscles w/enough glucose
  • muscle breakdown (Myoglobinuria), myoglobin in urine
39
Q

GSD VI

A

Hers Disease

  • deficiency in liver glycogen phosphorylase
  • prevent glycogen breakdown in liver (hepatomegaly)
  • low blood glucose lvls that cannot be brought up

SFM (Scientific Foundations of Medicine) (20 decks)

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