Glycolysis

Question 1

Types of regulation

Answer 1

Thermodynamic (substrates inc NAD:NADH, ATP:ADP)
Kinetic (allostery, phos)
Hormonal (usu via kinetic, genetic)
Genetic (long term, transcription, expression)

Question 2

Monosaccharides

Answer 2

Pentose
 - ribose, deoxyribose 
Hexose
 - glucose
 - mannose
 - galactose
 - fructose 

Have transporters in epithelium of small intestine
Most cyclic in solution (aldehyde less reactive)

Question 3

Disaccharides

Answer 3

• sucrose = glu a1-b2 fruc
• lactose = galac b1-a4 glu
• maltose = glu a1-a4 glu

Need enzymes in brush border for absorption

Question 4

Polysaccharides

Answer 4

Cellulose = glu b1-4 glu
 - we can't break down 
Starch = glu a1-4 glu
 - need alpha-amylase 
Glycogen = glu a-4 glu with a1-6 branches
 - need amylase, isomaltase

Question 5

Reducing sugars

Answer 5

“Benedict’s test”
Terminal aldehyde reduces cuprous citrate -> red
Also glycosylate amines of proteins (ex A1c in diabetes)

Glucose 
Galactose 
Lactose 
Maltose 
Fructose - only in aldehyde vs ketone isomer

Question 6

Lactose intolerance

Answer 6

Usu acquired -> >50% of adults
No lactase -> lactose to colon -> fuel source for bacteria -> H2 gas, acetaldehyde, EtOH, toxins
Dx with H2 gas in breath, hyperglycemia from lactose

Question 7

Glucose transport

Answer 7

Facilitated diffusion (reversible, driven by gradient) 
Regulated by expression and sequestration

ex GLUT 4 muscles, adipose = insulin dep
GLUT 1 RBCs = constitutive

Question 8

Hexokinase

Answer 8

Glucose + ATP -> G6P + ADP
Irreversible, G6P now trapped

Low Km -> active at low concentrations
Direct inhibition by G6P

Glucokinase -
High Km -> predominant at high concentration
- liver -> metabolism
- pancreas -> insulin release

Question 9

Glycolysis overview

Answer 9

Anaerobic - used in every cell
(exclusive in RBC bc no mitochondria)
Glucose + 2 ADP + 2P -> 2 Lactate + 2 ATP
requires input of 2 ATP -> net yield of 2

Question 10

PFK1

Answer 10

Phospho-fructo-kinase 1
Fructose6P + ATP Fru1,6BisP + ADP

Allosteric regulation
(+) AMP, Fruc 2,6 bisP
(AMP from adenylyl kinase: 2 ADP -> ATP + AMP) (-) ATP, citrate

Question 11

PFK2

Answer 11

Indirect regulator of PFK1
(Fruc2,6bisP stimulates PFK1

Bi-functional enzyme:
Fruc1P + ATP Fruc2,6bisP + ADP

(+) dephosphorylated -> PFK2 active
(+) insulin via protein phosphatase
(-) phosphorylated -> bisphos 2 active (reverse)
(-) glucagon via PKA

Question 12

Pyruvate kinase

Answer 12

Phosphoenol purvate + ADP -> pyruvate + ATP
(final step of glycolysis)

(+) Fruc 1,6 bisP
(+) phosphorylation (hormonal)
(-) ATP
(-) cancer - expresses slower PKM-2

Question 13

Lactate dehydrogenase

Answer 13

Pyruvate + NADH -> lactate + NAD+
(regenerates NAD+, lactate transported out for continued glycolysis)

Reversible:
(+) NADH
(-) lactate

Isoenzymes:
(+) M (muscle) -> forward
(-) H (heart, liver) -> captures lactate

Question 14

Pentose phos pathway

Answer 14

Alternative for G6P

• makes ribose 5-P for nucleotides
• energy from 5-C sugars
• regenerates NADPH (necessary to detox reactive O2 species, ie via glutathione)

Question 15

Glucose6P dehydrogenase

Answer 15

First step of pentose pathway
Necessary for oxidative stress (via glutathione)
- esp RBCs, no other source of NADPH

(+) NaDP+