carbohydrate function and metabolism

Question 1

what are the four functions of carbohydrates?

Answer 1

metabolic fuel
components of DNA and RNA
components of proteins
cell wall structure in bacteria and plants

Question 2

in what form is carbohydrate transported in the blood?

Answer 2

alpha-d-glucose

Question 3

what form does carbohydrate exist in in solution?

Answer 3

pentoses and hexoses exist primarily as cyclic molecules

Question 4

what types of chemical reactions that modify carbohydrates can occur?

Answer 4

aldehyde groups can be oxidized or reduced
carbohydrates can be attached to proteins and other molecules by glycosidic linkages
carbohydrates modify the properties of other molecules, such as proteins

Question 5

what are polysaccharides? (what are they made of and how are these molecules linked?)

Answer 5

polymers of multiple monosaccharides

linked by glycosidic bonds

Question 6

what is glycogen made of?

Answer 6

polymer of glucose

storage form of glucose

Question 7

how is glucose metabolized anaerobically?

Answer 7

by glycolysis or the pentose phosphate pathway

Question 8

how do red blood cells metabolize glucose?

Answer 8

only by glycolysis or the pentose phosphate pathway

Question 9

how is glucose metabolized aerobically?

Answer 9

in O2 utilizing cells, converted to CO2

Question 10

how and where is glucose stored?

Answer 10

as glycogen in the liver and muscle

Question 11

what materials can the liver use to synthesize glucose?

Answer 11

lactic acid and some AA

Question 12

equation for glycolysis?

Answer 12

glucose + 2ADP => 2 lactate + 2 ATP

note: lactate not phosphorylated and exits cell

Question 13

what inhibits hexokinase? what inhibits glucokinase?

Answer 13

hexokinase inhibited by G-6-P

glucokinase not inhibited by G-6-P

Question 14

what are the steps in insulin secretion?

Answer 14

1: glucose enters cell
2: ATP made via glycolysis
3: ATP closes K+ channels
4: increased K+ membrane depolarization cause Ca channels to open
5: Ca promotes exocytosis

Question 15

what does PFK-1 do?

Answer 15

converts F-6-P to F-1,6-bisphosphate
so basically just puts a P on C1
in glycolysis

Question 16

what regulates PFK-1?

Answer 16

ATP and citrate allosterically inhibit

F-2,6-BP allosterically activate - typically overcomes ATP inhibition

Question 17

What does PFK-2 do?

Answer 17

converts F-6-P to F-2,6-bisphosphate and so regulates PFK-1 activity (2,6 activates PFK-1)
both a kinase and a phosphatase
when acts as phosphatase, creates F-6-P

Question 18

what is the equation for the aldolase reaction?

Answer 18

F-1,6-BP => DHAP + G-3-P

has the highest gibbs free energy to overcome

Question 19

what does G-3-P dehydrogenase do?

Answer 19

aka GAPDH
G-3-P is oxidized by NAD => NADH
forms 1,3-bisphosphoglycerate
mechanism involves cystein acting as nucleophile, thiohemiacetal intermediate

Question 20

what does 3-phosphoglycerate kinase do?

Answer 20

converts 1,3-biphosphoglycerate to 3-phospoglycerate
thermodynamic favorability of the reaction is used to synthesize ATP
RBCs synthesize 2,3-bisphosphoglycerate from 1,3-BPG

Question 21

what does pyruvate kinase do?

Answer 21

coverts 3-phosphoglycerate to PEP
irreversable
thermodynamic favorability creates ATP

Question 22

what regulates pyruvate kinase?

Answer 22

allosterically inhibited by ATP

Question 23

what does lactate dehydrogenase do?

Answer 23

pyruvate is reduced by NADH
results in large free energy drop - reaction coupled with GAPDH reaction - LDH supplies NAD+ for GAPDH and GAPDH supplies NADH for LDH
reversable

Question 24

what are the different isozymes of lactate dehydrogenase?

Answer 24

there’s H and M
H4 in heart is ideally suited to oxidize lactate
M4 in muscle and liver ideally suited to reduce pyruvate

Question 25

what enzymes break down disaccharides? what are their substrates and products?

Answer 25

maltase: maltose => 2 glucose molecules
sucrose: sucrose => glucose and fructose
lactase: lactose => glucose and galactose

Question 26

what does fructokinase do?

Answer 26

converts fructose to F-1-P

Question 27

what happens if there’s F-1-P aldoase deficiency?

Answer 27

F-1-P aldolase converts F-1-P (open ring) to glyceraldehyde

without the enzyme, get buildup of F-1-P and liver damage

Question 28

what happens to the glyceraldehydes made from fructose?

Answer 28

can be converted to G-3-P in glycolysis pathway or to glycerol
first step to make glycerol requires ATP

Question 29

what causes fructose intolerance? what are the results?

Answer 29

due to lack of type B aldolase
results in buildup of F-1-P that damages liver
depletes ATP
inhibits glycogen phosphorylase
causes hypoglycemia as a result