metabolic pathways Flashcards
anabolic reactions
build up molecules
require energy (ATP)
catabolic reactions
break down molecules
release energy stored in chemical bonds
cellular respiration
short definition
entire process by which ATP is generated using glucose and oxygen
cellular respiration
3 phases
glycolysis
krebs cycle
oxidative phosphorylation
glycolysis
1 glucose → 2 pyruvate
produces (net) 2 ATP and 2 NADH
where does glycolysis occur?
cytoplasm
does glycolysis require oxygen?
no!
anaerobic process
glycolysis: rate-determining step
enzyme
phosphofructokinase
fructose-6P to fructose-1,6 bisP
what process substituted kreb’s if oxygen is absent?
in humans
lactic acid fermentation
fermentation
pyruvate + NADH → lactate and NAD+
NAD+ is used again in glycolysis so more ATP can be produced
krebs cycle
pyruvute from glycolysis → acetyl-coA → cycle
produces 2 ATP, 6 NADH, and 2 FADH2 per glucose
glycogen
the stored form of glucose that’s made up of many connected glucose molecules
what are the bonds that connect the glucose chains of glycogen
alpha-1,4-glycosidic bonds
what are the bond that create branches in glycogen
alpha-1,6-glycosidic bonds
glycogenesis
formation of glycogen from glucose monomers (for storage)
where is most glycogen stored?
skeletal muscle and the liver
glycogenolysis
converts glycogen back to glucose
(glycogen breaks down to glucose 1P and glucose)
gluconeogenesis
the production of NEW glucose from noncarbohydrate sources (ex. fat, amino acids, lactate, pyruvate, etc.) when glycoggen stores run out
almost reverse of glycolysis; has a diff path for the 3 irr. steps
gluconeogenesis: pyruvate to PEP
lactate → pyruvate → oxaloacetate → PEP
or
amino acids → oxaloacetate → PEP
note: pyruvate → OAA requires ATP, OAA → PEP requires GTP
pentose phosphate pathway
glucose → glucose 6P → ribose 5P and glycolysis intermediates
gluconeogenesis: fructose 1,6 bisphosphate → fructose 6P
enzyme
fructose 1,6 bisphosphatase
gluconeogenesis: glucose 6P → glucose
uses enzyme glucose 6 phosphatase
(instead of hexokinase of reverse reaction)
what are the 2 key products of the pentose phosphate pathway
1) ribose-5-phosphate (pentose)
2) NADHPH (phosphate)
what is the ribose-5p from PPP used for
to create DNA and RNA
what is the NADPH created in PPP used for?
1) donating electrons for anabolic reactions (ex. fatty acid synthesis)
2) regenerate anti-oxidants
pentose phosphate pathway: 2 phases
1) oxidative phase
2) non-oxidative phase
pentose phosphate pathway oxidative phase
glucose 6P → ribulose 5P
NADP+ → NADPH (x2)
pentose phosphate pathway: nonoxidative phase
ribulose 5p → ribose 5P
ribose-5P is used for nucleotide synthesis to make DNA/RNA
other intermediates are metabolites of glycolysis (fructose 3P and glyceraldehye 6P)
ATP used/released during PPP
NONE!
this makes PPP unique from other carbohydrate metabolism
fatty acid synthesis
conversion of excess glucose → fatty acids
glucose → pyruvate → acetyl-coA (in mitochondria) → citrate → acetyl-coA (in cytoplasm) + OAA
acetyl coA → acetyl coA carboxylase (RLS) → malonyl coA → palmitic acid (fatty acid)
fatty acid oxidation
fatty acids → acetyl coA
where does fatty acid synthesis from glucose occur
in the cytoplasm of liver cells
