Overview of Carbohydrate Metabolism Flashcards
1
Q
Main metabolic pathways of carbohydrates
A
- Glycolysis
- The TCA cycle
- Gluconeogenesis
- Glycogen synthesis and breakdown
- The Pentose Phosphate Pathway
2
Q
Oxidation definiction
A
- transfer of electrons from a reduced molecule to an acceptor
- reduced molecule = contains lots of potential chemical energy (electrons)
- e.g. glucose
3
Q
Fxn of “linked enzyme pathways”
A
- facilitate the stepwise modification of the parent molecule in an energy-efficient manner
- e.g. glycolysis
4
Q
Km definition
A
- concentration of substrate @ which the rxn proceeds at half maximal rate
- low Km = substrates have strong affinity for enzyme; rxn will proceed @ low substrate concentrations
5
Q
Vmax definition
A
- Vmax = maximal rate of rxn
- high Vmax = rxn will produce a lot of product over a short period of time
6
Q
Characteristics of/clues to “key steps” in biochemical pathways
A
- step in which important molecule changes location
- e.g. enters/leaves cell, mitochondria,etc
- step in which energy is used to transition from one molecular state to another
- e.g. addition of phosphate group
- rate limiting step
7
Q
Key steps in glycolysis
A
- Glucose ==> cytoplasm via glucose transporter
- Glucose + ATP ==> Glucose-6-P
- G6P is now trapped in cell
- G6P + Phospho-fructo-kinase (PFK) + ATP ==> Fructose 1,6-biphosphate
- activating step
- Fructose 1,6-bis-P ======> Pyruvate + ATP + NADH
- pyruvate = 3 Carbon compound
8
Q
Pyruvate destination: oxygen vs. no oxygen
A
- if O2 + mitochondria present:
- pyruvate ==> mitochondria
- pyruvate ==> acetyl CoA ==> TCA cycle
- ==> complete oxidation to CO2 & generation of NADH & FADH2
- energy of NADH & FADH2 ==> electron transport chain @ wall of mitochondria ==> O2 ==> production of ATP & H2O
- if NO O2 or mitochondria:
- pyruvate ==> lactate ==> exported from cell
9
Q
Steps of TCA cycle
A
- pyruvate ==> mitochondria ==> acetyl-CoA
- acetyl-CoA ==> TCA cycle = circle of linked enzymatic reaction
- ==> CO2 production + NADH + FADH2 + GTP (“energy carrier” molecules)
- NADH & FADH2 ==> electron transport chain
10
Q
Primary fxn of glycolysis
A
The purpose of glycolysis is the generation of energy and useful chemical intermediates from the breakdown of glucose
11
Q
Primary fxn of gluconeogenesis
A
- @ negative energy balance, the liver and to a lesser extent the kidney produce glucose.
- Lactate, or glycerol, or AA → liver → glucose
- The process of gluconeogenesis is essentially glycolysis in reverse except that it uses different enzymes and is regulated in an opposite manner.
12
Q
Primary fxn of glycogen synthesis/breakdown
A
- Glycogen synthesis: A rapidly available source of glucose for oxidative needs when the body needed energy is glucose stored within tissues as glycogen. This polymer of glucose is synthesized from glucose-6-P.
- Glycogen breakdown: glycogen is a highly branched polymer. This allows the rapid release of many glucose molecules when needed.
13
Q
Primary fxn of TCA cycle
A
- TCA cycle is at the heart of oxidative metabolism
- circle of linked enzymatic reactions
- TCA cycle provides a flexible circuit (like a roundabout at an intersection) into which a variety of carbon skeletons can enter and be modified while always replenishing substrates within the cycle.
14
Q
Primary fxn of electron transport system
A
- linked reactions of the electron transport system are separate from the TCA cycle
- occur @ inner mitochondrial membrane and the space between the inner and outer mitochondrial membranes
- ==> conversion of O2 to H2O and ADP to ATP in a process known as oxidative phosphorylation
15
Q
Glucose levels impact on metabolic pathways
A
- When glucose is abundant, glycolysis predominates.
- When glucose is in short supply, gluconeogenesis predominates.
- When more glucose is available, glycogen storage becomes a site for glucose disposal.
- When glucose is particularly abundant, it is directed to the pentose phosphate pathway
