Carbohydrates pt.3

ANSC - Lecture 7

metabolism

all the chemical reactions that occur in an organism

in what order do cells break down excess nutrients

carbohydrates, lipids, then amino acids

what are nutrients used for, if not for energy?

they are used to build up structure, they’re stored, or they’re excreted

how much energy released in catabolism is captured in ATP? where does the rest go?

40% captured in ATP, the rest is released as heat

anabolism (constructive metabolism)

simple substances are converted into more complex substances by living cells

functions of anabolism

• performance of structural maintenance and repairs

• support of growth

• production of secretions

• building of nutrient reserves

catabolism (destructive metabolism)

breaking down of complex substances into more simple compounds

list the priorities of absorbed glucose

1st priority: glycogen storage - stored in muscle and liver

2nd priority: provide energy - oxidized to ATP

3rd priority: stored as fat - only excess glucose (stored as triglycerides in adipose)

glycolysis

sequence of reactions that converts glucose into pyruvate

true or false: glycolysis does not require oxygen

true

where does glycolysis take place in the cell?

cytoplasm

what are the three fates (usages) of pyruvate?

• conversion to lactate (anaerobic)

• conversion to alanine (amino acid)

• entry into TCA cycle via pyruvate dehydrogenase pathway (create ATP) *most important

in anaerobic glycolysis, how much ATP is produced?

2 ATP

how are VFA’s produced?

by bacteria in the fermentation of pyruvate

function of acetate

energy source and for fatty acid synthesis

function of propionate

used to make glucose through gluconeogenesis

function of butyrate

energy source and for fatty acid synthesis; some use and metabolism by rumen wall and liver before being available to other tissues

where are VFA’s oxidized?

TCA cycle

how much ATP does acetic acid yield? propionic acid? butyric acid?

acetic - 10 ATP

propionic - 18 ATP

butyric - 27 ATP

pentose phosphate pathway

secondary metabolism of glucose

functions of pentose phosphate pathway

produces NADPH (required for fatty acid synthesis), generates essential pentoses (used for synthesis of nucleic acids)

function of liver in glycogenesis

• use glycogen to export glucose to the bloodstream when blood sugar is low

• glycogen stores are depleted after approximately 24 hours of fasting (in humans)

function of skeletal muscle in glycogenesis

more muscle than liver, so more glycogen in muscle overall

• use glycogen for energy only

• use already-made glucose for synthesis of glycogen

fates of glucose in the fed state? fasted state?

fed state:

• stored as glycogen (liver, skeletal muscle)

• storage as lipids (adipose tissue)

fasted state:

• metabolized for energy

• new glucose synthesized

when does synthesis and breakdown occur?

at all times, regardless of state

what are the primary regulators of gluconeogenesis?

insulin and glucagon

true or false: gluconeogenesis is vital for all animals

false, vital for certain animals (ruminants and other pre-gastric fermenters)

gluconeogenesis

synthesis of glucose from non-carbohydrate precursors during fasting in monogastrics

where does gluconeogenesis take place?

primarily in the liver, but can also occur in kidneys and small intestine

primary energy substrate for most monogastrics? for ruminants/pre-gastric fermenters?

MOST monogastrics - glucose

ruminant/pre-gastric fermenters - VFA

primary substrate for fat synthesis is most monogastrics? ruminants?

most monogastrics - glucose

ruminants - acetate

extent of glucose absorption from gut in most monogastrics? ruminants?

most monogastrics - extensive

ruminants - little to none

where does required glucose come from in terms of a fasting situation in non-ruminants?

glycogenolysis, lipolysis, and proteolysis

glycogenolysis

breakdown of mobilization of glycogen stored by glucagon

glucagon

hormone secreted by pancreas during times of fasting

lipolysis

mobilization of fat stores stimulated by glucagon and epinephrine

proteolysis

the breakdown of muscle protein with release of amino acids

ruminants vs non-ruminants:

cellular demand for glucose? importance of gluconeogenesis? ketone production?

cellular demand for glucose:

nonruminant = high ruminant = high

important of gluconeogenesis:

most monogastrics = less important ruminant = important

ketone production:

most monogastrics = abnormal situation ruminant = normal