BIO 205 Lecture Notes - Lecture 27: Glycogen Synthase, Glycogen Phosphorylase, Glyceraldehyde 3-Phosphate
2 May 2018
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Lecture #27 Fates of G6P
Pentose phosphate shunt
1. Alternative fates for G6P
a. Isomerized into fructose-6-phosphate and ultimately produce
ATP
b. Converted into glycogen
c. Converted into a ribose, a pentose
i. Oxidizes the aldehyde ending of G6P into a carboxylic acid
group, then released as CO2
ii. Provides energy
iii. This is called the pentose-phosphate shunt, since ribose is
a pentose and the pathway has phosphate attaches to the
intermediates
2. Structure of NAD and NADP
a. Phosphate group in NADP+ is attahed to the 2’ OH group of the
adenosine nucleotide, and is far from the redox center of
nicotinamide nucleotide
3. Pentose phosphate shunt
a. First phase: oxidative phase: converts glucose from a 6 carbon
aldose chain ending in aldehyde into a 6 carbon chain ending in
carboxylic acid group; oxidation of glucose is now balanced by
reduction of NADP+, NADP+ is converted into NADPH. Now with
carboxylic acid group at the end, you can convert the 6 carbon
chain into CO2 and a 5C chain. The reaction is an oxidative
decarboxylation, generating another NADPH. The produce,
ribulose-5-phosphate is a ketose.
b. 6C glucose + 2NADP _> ribose 5C + CO2 1C + 2NADPH
Glycogen metabolism: reaction steps
4. Liver buffers the glucose in the blood
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2
a. Brain consumes glucose but will not import fats
b. Brain stores no glucose in the form of glycogen
c. Needs a constant steady supply of glucose arriving in the
bloodstream
d. Body maintains blood glucose level of 5 mM glucose
e. Body needs to find a way to have glucose not to get too high or
low in the blood
f. The liver provides this buffering role, when levels rise above 5
mM, the liver imports glucose and converts into glycogen
g. When blood glucose drops below 5 mM, the liver converts the
glycogen back into glucose and delivers glucose back into the
blood stream to restore the buffered glycogen
5. Glycogen synthase vs glycogen phosphorylase
a. Pyrophosphorylase takes PPi out of solution and pastes it onto
an organic molecule, UDP- glucose
b. Synthase has two substrates, 2 molecules join to make a larger
product
c. The net removal of phosphates from UTP and G6P provide two
Pi’s provides the energy for anaoli iosynthesis of glyogen
polymer
Hormones affecting glycogen metabolism: glucagon, insulin, and adrenalin
6. Chemical classes of hormones
a. Lipid soluble: nonpolar, freely able to diffuse, ex: steroid
hormones and thyroid hormones
b. Water soluble: not able to penetrate membranes, binds to
receptors on outside cells, ex: glucagon and insulin
7. Mechanism of action: steroid hormones: bind in the nucleus
a. Not very soluble, so carried through bloodstream and
transported by a transporter protein that binds the nonpolar
hormone
b. Occasionally dissociates from the transporter and diffuses in
membrane
c. They may bind to a specific protein and change conformation
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Document Summary
Pentose phosphate shunt: alternative fates for g6p, isomerized into fructose-6-phosphate and ultimately produce. Now with carboxylic acid group at the end, you can convert the 6 carbon chain into co2 and a 5c chain. The reaction is an oxidative decarboxylation, generating another nadph. The produce, ribulose-5-phosphate is a ketose: 6c glucose + 2nadp _> ribose 5c + co2 1c + 2nadph. Pi"s provides the energy for ana(cid:271)oli(cid:272) (cid:271)iosynthesis of gly(cid:272)ogen polymer. Adrenalin is the primary messenger, camp is secondary, protein kinases activated: kinases are enzymes that attach phosphate groups to other proteins, hormone structure: insulin. Insulin begins as a single protein chain containing 3 disulfide bridges. Cleaved, leaving the mature form consisting of a and b chains joined by disulfides. There are 51 amino acids in the final structure. Protein hormone, smaller than insulin, only 29 amino acids. Substituted amine which is derived from tyrosine, also called adrenalin, secreted by adrenal glands.
