Carb metabolism

Question 1

Besides being broken down for glucose, carbs also have other roles such as:

Answer 1

precursors of essential intermediates in systemic biochemical pathways
components of glycoproteins

Question 2

Anabolic phase of CHO metabolism

Answer 2

• begins with food ingestion, lasts several hours (energy stores replenished as caloric intake exceeds needs)
• glycogen synthesis is stimulated in liver and muscle
• FA synthesis and TAG formation are stimulated in liver and adipose tissue

Question 3

After a mixed meal which concentrations rise and which fall?

Answer 3

plasma glucose, triglyceride and AA concentrations rise

plasma FFAs, ketones and glycerol decrease

Question 4

Catabolic phase

Answer 4

• begins 4-6h after the last meal and continues until next meal (energy stores in liver and muscle and adipose are used for energy)
• glucose obtained via glycogenolysis and gluconeogenesis
• lipolysis in adipoctes increases considerably

Question 5

What are the main carbs in monogastrics

Answer 5

starch, sucrose and lactose

Question 6

Digestion of starch begins in?

Answer 6

the oral cavity with salivary amylase

Question 7

Monosaccharides broken down include:

Answer 7

starch, glycogen–> glucose
sucrose–> glucose + fructose
lactose–> glucose + galactose

Question 8

Monogastric vs ruminant CHO digestion

Answer 8

mono:
glycolysis in monogastric animal cells–> energy + pyruvate used directly by animal cells
ruminant:
glycolysis in bacterium–> energy + pyruvate used by bacterium–> ruminant absorbs VFAs–> used for energy or glucose synthesis

Question 9

Once we have glucose in the bloodstream of any animal how do we get it into cells?

Answer 9

1. GLUT proteins carry glucose into cells
2. GLUT 2 in liver is always active- always taking in glucose from diet to store and glycogen
3. Main transporter in skeletal muscle and adipose (GLUT 4) is most active when insulin levels are high

Question 10

Once in cell glucose is processed in 4 major ways

Answer 10

1. glycolysis- 1st step in the production of energy as ATP
2. glycogenesis - storing glucose as glycogen
3. hexose monophosphate pathway - synthesis of nucleic acids; synthesis of NADH)
4. glucuronate pathway- synthesis of proteoglycans and Vit C

Question 11

Glycolysis converts glucose into?

Answer 11

2 pyruvate molecules
NADH + H+
ATP
CO2

Question 12

For each glucose molecule metabolized _____ ATP molecules are consumed in the first phase of glycolysis

Answer 12

2

Question 13

Which enzyme in the glycolytic pathway is inhibited by ATP?

Answer 13

phosphofructokinase

so when energy stores are high the body does NOT keep splitting glucose to make inneeded energy

Question 14

Where does the pyruvate from glycolysis go?

Answer 14

goes to the citric acid cycle an aerobic process which is the next stage of cellular respiration

Question 15

NADH from the krebs cycle supplies energy for?

Answer 15

electron transport chain and oxidative phosphorylation to create an abundance of ATP- the H+ ions flow through ATP synthase

Question 16

One glucose molecule produces ____ ATP in the kreb cycle

Answer 16

36 ATP

Question 17

In herbivores, ______ from rumen or hindgut fermentation are used in place of pyruvate in herbivores

Answer 17

VFAs

Question 18

Glycolysis and glyconeogenesis are?

Answer 18

opposing processes

Question 19

Ruminants exist in a constant state of?

Answer 19

potential glucose deficiency

Question 20

Gluconeogenesis is a process whereby?

Answer 20

glucose is synthesized from metabollic intermediates and amino acids

Question 21

Glycogenesis first step

Answer 21

phosphorylation of glucose at the C-6 position

-done in the liver, facilitated by glucokinase (hexokinase IV)

Question 22

the rate of phosphorylation of glucose by hexokinase IV is directly proportional to?

Answer 22

glucose concentration

Question 23

Glycogenesis proceeds if ________ is converted to _______

Answer 23

glucose -6-phosphate
glucose-1-phosphate - which is then further metabolized resulting in the glucose molecule being added to a growing glycogen molecule by the enzyme glycogen synthase

Question 24

2 main functions of hexose monophosphate pathway

Answer 24

• generates reducing equivalents (NADPH) for the synthesis of fatty acids and steroids and the reduction of glutathione
• produces ribose-5-phosphate for nucleic acid synthesis

Question 25

Two main mechanisms are used to maintain blood glucose levels between meals

Answer 25

glycogenolysis

gluconeogenesis

Question 26

Explain process of glycogenolysis

Answer 26

cleaves glycogen to relase an intermediate which is converted to glucose-6-phosphate and then to free glucose, which is released into the blood stream

Question 27

How is lactate formed?

Answer 27

in muscle when oxygen supplies are inadequate and pyruvate cannot be used pyruvate accumulates and some of it combines with protons to form lactate

Question 28

what are other precursors for gluconeogenesis

Answer 28

amino acids
lactate
glycerol
propionate 
-these precursors enter the pathway at various points and undergo a process which is the reverse of glycolysis using some of the same enzymes