Metabolism, Digestion, Glycolysis

Question 1

metabolism

Answer 1

the sum of anabolic and catabolic pathways

Question 2

anabolic metabolism

Answer 2

synthetic pathways to build the subunits (amino acids, nucleic acids, etc) from smaller molecules and also put the subunits together to create the four classes of macromolecules from which all cellular structures are made. Require an input of energy either by coupling the +delta G synthesis reaction with ATP hydrolysis or by using the reducing power of NADPH2 or both

Question 3

catabolic metabolism

Answer 3

catabolic pathways hydrolyze the macromolecules back to subunits and break the subunits into simpler molecules. Most catabolic reactions have negative delta G values.

Question 4

Intermediary metabolism

Answer 4

pathways that connect via intermediates.

Question 5

3 pathways that harvest the free energy released as catabolism occurs

Answer 5

1. Glycolysis or fermentation
2. Krebs cycle/Citric acid cycle/TCA cycle
3. Electron Transport System

Question 6

amphibolic

Answer 6

pathways that are used for both synthesis and degradation

Question 7

Ways to regulate metabolism

Answer 7

1. Feedback regulation on allosteric enzymes that control a committed step
2. Repression or activation of genes to control the amount of new enzyme being synthesized (usually controlled at the level of transcription)
3. Compartmentalize reactions in different organelles

Question 8

Why is ATP an energy-rich molecule?

Answer 8

It has a highly negative delta G value because:

1. The negative charges on oxygens repel each other and encourage hydrolysis
2. More resonance structures stabilize ADP and Pi versus ATP
3. Water molecules stabilize ADP and Pi

Question 9

How does ATP power reactions that wouldn’t otherwise take place?

Answer 9

coupling of ATP hydrolysis to an otherwise unfavorable reaction. ATP plus the substrate accepting the phosphoryl group occupy the active site together.

Question 10

coupling

Answer 10

1. enzymatic coupling - 2 reactions going simultaneously in the same enzyme at the same time
2. metabolic coupling - a series of reactions. one reaction is being drawn forward by subsequent reactions

Question 11

what is the energy charge of a cell?

Answer 11

The amount of ATP available compared to ADP/AMP. The ratio of ATP:ADP.

Question 12

what are the irreversible steps in glycolysis and their enzymes

Answer 12

1. Hexokinase - converts glucose to glucose-6-phosphate
2. Phosphofructokinase - converts fructose-6-phosphate to fructose 1,6-bisphosphate by adding a phosphate
3. pyruvate kinase - converts PEP to Pyruvate

Question 13

net reaction of glycolysis

Answer 13

Glucose + 2Pi + 2 ADP + 2 NAD+ –> 2 pyruvate + 2 ATP + 2 NADH + 2H+ + 2H2O

Question 14

fermentation

Answer 14

cells go into fermentation under low-oxygen conditions. Without oxygen, there is no ultimate electron-acceptor where NADH (generated during glycolysis and Krebs) can dump its electrons. If NAD+ cannot be regenerated, then glycolysis cannot continue to run. Fermentation is the process of regenerating NAD+ by using the enzyme lactate dehydrogenase to transfer electrons from NADH onto pyruvate to form lactate.

Question 15

how do we generate energy under low-oxygen conditions?

Answer 15

1. Fermentation
2. creatine-phosphate serves as a store of phosphate that can be pulled off and put onto ADP to form ATP. (Creatine-phosphate has a high phosphoric transfer potential - higher than ATP - so there’s a large negative delta G value for transferring a phosphate off of it.)

Question 16

protein digestion

Answer 16

1. stomach - begins in the stomach when pepsinogen is activated to pepsin by the acidic ph of the stomach.
2. duodenum - oligopeptides enter the duodenum, an upper section of the small intestine, where they mix with enzymes and bicarbonate (secreted by the pancreas to neutralize the acidic ph coming in)
3. duodenum - pancreas also secretes other enzymes to aid in digestion, such as trypsin.

Question 17

carbohydrate digestion

Answer 17

1. mouth - alpha-amylase enzyme begins digestion in mouth by breaking alpha-1,4 linkages
2. stomach - nothing really happens here
3. duodenum - maltase and alpha-dextrinase are membrane-embedded enzymes that cleave maltose and alpha-1,6 bonds respectively. lactase is also present and digests lactose.
4. small intestine - continued digestion

Question 18

nucleic acids

Answer 18

digested by nucleases

Question 19

Lipids

Answer 19

• -Lipases hydrolize triglycerides and phospholipids to free fatty acids and glycerol. Bile acids are secreted by the gall bladder and are used to emulsify fats so lipase can interact with them.
• -In intestinal cell they are remade into triglycerides and packaged into particles (chylomicrons) for transport in the blood.
• -These particles are recognized and the contents hydrolyzed again by enzymes on the surface of muscle and adipose cells to deliver fatty acids to these cell types.

Question 20

alpha-amylase

Answer 20

enzyme that is found in the mouth that begins digestion of starches by cleaving alpha-1,4 glycosidic bonds

Question 21

pepsinogen

Answer 21

the inactive form of pepsin. It is activated to pepsin when it is secreted into the stomach. The acidic pH of the stomach activates it, as well as other pepsin molecules activating it.

Question 22

zymogen

Answer 22

the inactive form of an enzyme. A zymogen carries an extra amino acid attached to it. The cleaving of the extra amino acid activates the zymogen. ex: pepsinogen is the zymogen. pepsin is the active form.

Question 23

trypsinogen

Answer 23

inactive form of trypsin. When activated, trypsin digests protein in the duodenum/small intestine. Trypsinogen is activated by a peptidase found in the duodenum

Question 24

sodium bicarbonate

Answer 24

secreted by the pancreas into the duodenum to neutralize the acidic pH of the slurry coming into small intestine from the stomach

Question 25

alpha-dextrinase

Answer 25

found in the membrane of the small intestine, this enzyme cleaves alpha-1,6 glycosidic bonds

Question 26

maltase

Answer 26

cleaves maltose. found in membrane of small intestine

Question 27

lactase

Answer 27

cleaves lactose into its single units. found in membrane of small intestine.

Question 28

gall bladder role in digestion

Answer 28

secretes bile salts into duodenum to aid in digestion of lipids

Question 29

bile salts

Answer 29

emulsify lipids so that lipases can get close enough to them to digest them

Question 30

lipase

Answer 30

enzymes that digest lipids. Breaks up lipids into fatty acids and glycerol. Secreted by pancreas into small intestine (duodenum)

Question 31

what happens to fatty acid after it’s broken up from glycerol

Answer 31

Fatty acids form micelles and diffuse into intestinal cells, where they are repackaged into chylomicrons with glycerol and sent into the blood to be delivered to other tissues.

Question 32

chylomicron

Answer 32

lipoprotein that carries lipids through blood stream

Question 33

secretin

Answer 33

a hormone that causes the release of sodium bicarbonate from pancreas

Question 34

CCK

Answer 34

a hormone that stimulates the release of digestive enzymes from pancreas and secretion of bile salts from gall bladder. Also responsible for the sensation of satiety.

Question 35

Leptin

Answer 35

the hormone that initiates hunger pains

Question 36

1,3-bisphosphoglycerate

Answer 36

Has a higher phosphoryl transfer potential than ATP, so it is able to transfer phosphate onto ADP to form ATP. Makes sense that BGP is the compound in glycolysis that is the first step where ATP is generated. If we know how to make BGP, we know how to synthesize ATP. The formation of 1,3-BPG is the money step in glycolysis. We are using the energy from oxidation of 3-phosphate-glyceraldehyde (while reducing NAD+ to NADH) to take a phosphate from the medium and put it onto 3-phosphate-glyceraldehyde to form 1,3-bisphosphoglycerate.

Question 37

how do you make BGP?

Answer 37

start with glucose, divide it into two 3-carbon molecules and oxidize it from aldehyde to acid via glycolysis. i.e. we use a redox reaction to oxidize an aldehyde to an acid while NAD+ is reduced to NADH

Question 38

free energy of oxidation

Answer 38

the more reduced a carbon is, the more free energy is released when it is oxidized. CH4 has a lot of energy to release, whereas CO2 has zero.

Question 39

substrate level phosphorylation in glycolysis

Answer 39

PEP passing phosphate onto ADP to form ATP; 1,3-BGP passing phosphate onto ADP to form ATP

Question 40

what gets reduced in glycolysis?

Answer 40

as glucose is oxidized, NAD+ gets reduced to NADH

Question 41

who is intended as the ultimate electron acceptor in the oxidation of fuel molecules?

Answer 41

O2

Question 42

hexokinase

Answer 42

the first enzyme step in glycolysis. Phosphorylates glucose when it comes in the cell to trap it there. Glucose–> glucose-6, phosphate. Energy requiring step. Hexokinase has 2 roles: 1. phosphorylate glucose to trap it in cell; 2. raise the energy level of the molecule - makes the molecule more unstable so it’s more likely to go to product. Hexokinase is regulated by the product of its reaction - glucose-6-phosphate.

Question 43

phosphofructokinase

Answer 43

the enzyme step in glycolysis that is the 2nd irreversible step. Uses ATP to convert fructose-6, phosphate to fructose 1,6-bisphosphate. Regulated allosterically - it is inhibited by ATP and stimulated by AMP.

Question 44

money step in glycolysis

Answer 44

conversion of glyceraldehyde-3 phosphate to 1,3-bisphosphoglycerate by the enzyme glyceraldehyde 3-phosphate dehydrogenase. Uses a redox reaction to drive adding a phosphate from the medium onto glyceraldehyde-3-phosphate to make 1,3-BPG (which can then transfer its phosphate onto ADP to make ATP). NAD+ is reduced to NADH while glyceraldehyde-3-phosphate is oxidized to 1,3-bisphosphoglycerate. (Aldehyde–> “ate” means you’ve lost the hydrogen on the aldehyde)

Question 45

pyruvate kinase

Answer 45

the last irreversible enzyme step in glycolysis. This is the step where PEP is converted to Pyruvate, generating ATP in the process. Regulated allosterically by pyruvate (the product of its own reaction) and ATP.

Question 46

glucokinase

Answer 46

the enzyme primarily responsible for phosphorylating glucose in the liver is glucokinase instead of hexokinase. Glucokinase has a much higher Km (lower affinity) for glucose than hexokinase, so it traps glucose in the liver only when blood glucose levels are high (right after a meal), while the rest of the cells in the body trap glucose all other times.