BioChem Exam #3 Flashcards
1
Q
What are the Simple Sugars (glucose, fructose) used for?
A
Energy
2
Q
What are Complex Polymers used for?
A
Cellulose - structure;
Starch/Glycogen - energy storage;
Hormones, antibodies, communications, etc.
3
Q
What is the general formula for Carbs?
A
(CH2O)n;
Come as polyhydroxy aldehydes, ketones, and their derivatives and polymers;
Classified by degree of polymerization
4
Q
What are Monosaccharides?
A
Single units; Simple sugars; Large number of hydroxyl groups and polar; Water soluble; Taste sweet
5
Q
What are Oligosaccharides?
A
2-10 units
6
Q
What are Polysaccharides?
A
Many units
7
Q
How are Monosaccharides named?
A
- “-ose” ending;
- # of carbons;
- functional group (keto or aldo);
- Combine
8
Q
What is an Aldose?
A
Monosaccharide with the carbonyl group as an aldehyde;
On the END
9
Q
What is a Ketose?
A
Monosaccharide with the carbonyl group as a ketone;
In the MIDDLE
10
Q
What are Chiral Carbons?
A
Have 4 different attached groups;
Most carbs have one or more
11
Q
What is there is MORE than one chiral carbon?
A
Means there can be more than two stereoisomers
12
Q
How is the number of Stereoisomers (optical isomers) determined?
A
2^n, with n being the number of chiral carbons
13
Q
What are Enantiomers?
A
Non-superimposable mirror images;
Like our hands;
Members of each pair of stereoisomers
14
Q
What are Diastereiomers?
A
Members of different pairs of stereoisomers
15
Q
What is a D sugar?
A
-OH on the highest numbered chiral carbon is to the RIGHT;
Predominant form
16
Q
What is an L sugar?
A
-OH on the highest numbered chiral carbon is to the LEFT
17
Q
What are Aldotrioses?
A
3 carbons, aldehyde end;
1 chiral;
-D-glyceraldehye
18
Q
What are Aldotetroses?
A
4 carbons, aldehyde end;
2 chiral;
3 stereoisomers
19
Q
Aldotetroses
A
D-erythrose;
D-threose
20
Q
What are Aldopentoses?
A
5 carbons, aldehyde end;
3 chiral;
8 stereoisomers
21
Q
Aldopentose
A
D-ribose;
ALL -OH on the RIGHT
22
Q
What are Aldohexoses?
A
6 carbons, aldehyde end;
4 chiral;
16 stereoisomers
23
Q
Aldohexoses
A
- D-glucose
- D-mannose
- D-galactose
24
Q
How do you draw the fisher for Glucose?
A
“Right - Left - Right” for -OH’s (except bottom right for D)
25
What is an Epimer?
When the Fisher structure differs by ONLY ONE -OH placement
26
What is Mannose to Glucose?
Mannose is the C2 epimer to Glucose
| OH at C2 is on the LEFT instead of right
27
What is Galactose to Glucose?
Galactose is the C4 epimer to Glucose
| OH at C4 is on the LEFT instead of right
28
What does the Fischer of a KETOSE look like?
C=O is at C2;
Lose a Chiral Carbon that was at C2 in an aldehyde;
"-ulose" ending in naming
29
Ketoses
- Dihydroxyacetone (3 carbons)
- D-erythrulose (4 carbons)
- D-ribose (5 carbons)
- D-fructose (6 carbons)
30
What is D-Fructose to Glucose?
It is the KETOSE analogous to Glucose;
| Only differs in that the carbonyl (C=O) is at C2
31
How do ring structures form?
- Reaction between the CARBONYL group and the HIGHEST number chiral carbon;
- Internal hydroxyl groups don't move!;
- Make either a hemiacetal, acetal, hemiketal, or ketal
32
What is an Anomeric Carbon?
New chiral Carbon that is created in the formation of a ring structure;
From the Carbon that was in the Carbonyl;
Always on the RIGHT of the ring
33
How do you determine Alpha and Beta ring structures?
By the position of the -OH on the ANOMERIC Carbon (new chiral center);
Alpha = DOWN (right in fischer):
Beta = UP (left in fischer)
34
For Haworth, the ANOMERIC Carbon is...
on the RIGHT
35
For Haworth, the RING O is....
ABOVE and to immediate LEFT of the Anomeric C
36
For Haworth, groups to the RIGHT in fishcer are...
DOWN in the ring
37
For Haworth, groups to the LEFT in fischer are...
UP in the ring
38
For Haworth, the terminal -CH2OH of D-sugars is...
UP
| all the sugars we draw!
39
What is Furanose?
A 5-membered ring;
| Fructose, ribose
40
What is Pyranose?
A 6-membered ring;
| Glucose
41
What are Conformational structures?
Some enzymes might require the CHAIR confirmation
42
What is Mutarotation of Monosaccharides?
- "opening and closing" of the ring structure;
- Allows the going back and forth between enantiomers (Alpha and beta confirmations);
- Beta to Open Chain to Alpha, and vice versa;
- Reversible reaction
43
What is the Open Chain form?
When there is a FREE aldehyde or ketone;
| No bond to the highest chiral carbon is formed in this state
44
How often is Glucose in each enantiomer?
- About 62% Beta;
- About 38% Alpha;
- Remaining .02% open chain
45
Why is so little time spent in the Open Chain form?
- Rings are thermodynamically more stable;
| - On average, less than 10% of molecules are ever in the the open chain
46
What is Isomerization of Monosaccharides?
- Under alkaline (basic) conditions,there is reversible interconversion between the ketose, aldose and epimer forms of the compounds;
- Aldose-Ketose Interconversion;
- Epimerization
47
Isomerization of Glucose
- Fructose (ketose) to
- Glucose (aldose) to
- Mannose (C2 epimer)
48
What is Oxidation of Monosaccharides?
- An ALDEHYDE can be oxidized and act to REDUCE other compound;
- It acts as a REDUCING AGEN;
- Requires a FREE aldehyde
49
What happens to the aldose when it is oxidized?
it becomes an Aldonic Acid
| Glucose becomes gluconic acid
50
How can a KETONE be involved in an oxidation reaction?
Under ALKALINE (basic) conditions, ketoses can be converted to aldoses, and then be oxidized
51
What are Reducing Sugars?
Aldoses and ketoses that can convert to open chain form
52
How does Oxidation continue if it is IRREVERSIBLE?
Because the open chain and ring forms exist in equilibrium, removing open chain to be oxidized, will push equilibrium to create more open chain structures that can be used
53
What is Esterification of Monosaccharides?
-Addition reaction (Condensation);
-Between an alcohol and a carboxylic acid;
EX: React an alcohol (-OH group) with Phosphoric acid (H), removes a molecule of water and adds phosphate group the R group of the alcohol by a bond to the oxygen left on the acid
54
What are the Substitutions of Monosaccharides (derivatives)?
- Amino sugars
- Deoxysugars
- Glycoside formation
55
What makes an Amino Sugar?
An (-OH) group on the sugar is replaced by an AMINE group (NH3+)
56
What are Deoxysugars?
- An (-OH) group on the sugar is replaced by JUST a Hydrogen
| - Missing an Oxygen (EX: Deoxyribose in DNA)
57
What is Glycoside formation?
- A SUGAR (hemiacetal/hemiketal) becomes bound to a functional group (such as an alcohol) with a glycosidic bond;
- Hydrogen on Hydroxyl group on C1 is replaced with an acetal group;
- Makes a GLYCOSIDE (acetal/ketal) and water;
- Must have the CYCLIC structure to occur
58
How does a Glycoside change the functionality of the monosaccharide?
- When the glycoside forms, the ring is now "locked" and won't reopen;
- NO longer a Reducing Sugar = NON-REDUCING;
59
Why can't a monosaccharide reduce after glycoside formation?
- The new glycosidic bond between the C1 (anomeric) carbon and the Oxygen of the acetal group, stabilizes the alpha and beta form (ring);
- Forms a disaccharide when the second (-OH) of the reaction is an alcohol
60
How do you name Disaccharides?
1. Name the first sugar on the LEFT (hemiacetal or hemiketal donor)
a. D or L
b. Sugar name with "-osyl" ending
c. Ring size
2. Anomeric configuration (alpha/beta)
3. Positions of linkages
4. Name the second sugar on the RIGHT
61
Full name of MALTOSE
- D-glucosyl(p) - alpha (1,4) - D-glucose;
- Reducing
- We can digest
62
Full name of CELLOBIOSE (makes cellulose)
- D-glucosyl(p) - beta (1,4) - D-glucose;
- Reducing
- We CANNOT digest
63
Full name of LACTOSE
- D-galactosyl(p) - beta (1,4) - D-glucose;
- Reducing
- We can digest
64
Full name of SUCROSE
- D-glucosyl(p) - alpha, beta (1,2) - D-fructose
- NON-reducing (both anomeric are in the linkage)
- We can digest
65
What form are Oligosaccharides normally found in?
Glycoprotein with proteins;
| Glycolipids with lipids
66
What are N-linked Oligosaccharides?
```
(-OH) of the sugar + (-NH2) of amide group on the protein;
Carbon-Nitrogen bond;
-Asparganine
-Glutamine;
(Remove a water to make bond)
```
67
What are O-linked Oligosaccharides?
```
(-OH) of the sugar + (-OH) of the protein;
Carbon-Oxygen bond;
-Serine (mostly)
-Threonine
-Tyrosine
```
68
What are HOMOpolysaccharides?
Made of 1 type of monosaccharide unit;
Usually glucose, especially for energy storage as Starch and glycogen;
Also Cellulose
69
What is Starch? (Homopolysaccharide)
- Major storage form of carbs in plants;
- Polyglucose (many glucose)
- Major links are ALPHA (1,4)
- Branches are ALPHA (1,6)
70
What are the 2 different forms of Starch?
- Amylose
| - Amylopectin
71
Characteristics of Amylose
- Linear, Unbranched;
- Single chain of alpha (1,4) links;
- NO branches
- Forms a helix with internal Hydrogen bonding
- Relatively INSOLUBLE in H2O due to self-interacction of helix
72
Characteristics of Amylopectin
- Alpha (1,4) backbone with Alpha (1,6) branches
- Branched about every 20-25 residues;
- More SOLUBLE due to LESS internal H-bonding
- Digested and absorbed much quicker than amylose due to the presence of more branches that enzymes can act on
73
What is Glycogen? (Homopolysaccharide)
- Major form of carb storage in animals;
- HIGHLY branches about every 8-12 residues;
- Stored in LIVER and skeletal MUSCLES
74
What makes Glycogen a readily available energy source?
- Being HIGHLY BRANCHED makes very soluble and more allows for enzymatic breakdown and FASTER release of glucose;
- Acted upon at EACH branch
75
Why is the quick release of Glucose from storage needed in the body?
- Quick access to energy in the muscles during "fight or flight" responses;
- Maintenance and control of blood glucose levels by the liver when we eat
76
What is Cellulose? (Homopolysaccharide)
- STRUCTURAL carb found in the cell wall of plants;
- Polyglucose
- BETA (1,4);
- Linear, UNbranched
- NO nutrient value;
- NOT digested by humans;
- Very INSOLUBLE due to lots of Internal H-bonding
- Appears as sheets due to beta bonding
77
Why can Cows and other animals gain nutrients from Cellulose?
-Certain microorganisms that live in the intestinal tract of ruminant animals breakdown the cellulose and then the animals can utilize the products
78
What are HETEROpolysaccharides?
- Consists of MORE than one type of monosaccharide unit;
- Glucosaminoglycans
- Glycoconjugates
79
What are Glucosaminoglycans, GAGs? (Hetero)
- Long unbranched polysaccharides consisting of a repeating disaccharide unit (same 2 sugars);
- consists of an AMINO SUGAR and uronic sugar or galactose (SUGAR ACIDS, -SO4 2- derivatives);
- Highly polar due to charge-charge repulsion making them highly negative so traps water;
- Turns gel-like due to absorbed water
80
What are GAGs used for?
- Useful as a lubricant or shock absorber;
- Gel structure can absorb physical stress;
- Found in Cartilage and Arterial Walls
- Heparin is used as an anticoagulant
81
What is Heparin?
A highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule
82
What are Glucoconjugates? (Hetero)
- The general classification for carbohydrates covalently linked with other chemical species such as proteins, peptides, lipids and saccharides;
- Peptidoglycans
- Glycoproteins
- Glycolipids
83
What are Peptidoglycans? (conjugate)
- Polymer of sugars and amino acids;
- Major portion is the Carb;
- Mostly GAG's (repeating, modified disaccharides)
- Can be N-linked or O-linked;
- Vary in length of the oligopeptides that are attached
- Forms mesh-like layer around plasma membrane of cell making the cell wall
84
What are Glycoproteins? (conjugate)
- Protein with carb attached
| - Can be N-linked or O-linked
85
What are the characteristics of the CARB part of GLYCOPROTEINS?
- LACK sugar acids and sulfates;
- Very short carb (1 or many individual);
- Often branched
- Informational, seldom repeating;
- Protect from denaturation;
- Help protein folding
- Transport through the cell by helping solubility in the aqueous cytoplasm
86
What are Glycoproteins used for?
- Hormones;
- Enzymes (prosthetic groups);
- Antifreeze (blood of artic fish);
- Antibodies to fight disease;
- Antigens (cell-cell communication) = found on RBC surface and gives blood types and characterization
87
What are Glycolipids?
- Lipids with carbs attached;
| - Provide energy and serve as markers for cellular recognition
88
What are Glycolipids used for?
- Membrane components (gangliosides in brain gray matter);
- Found in gram-bacteria;
- Serve as antibody targets
- Some are toxic to humans
89
Characteristics of the CARB portion of GLYCOLIPIDS?
- Used for cell-cell recognition as markers;
- extend from the phospholipid bilayer into the aqueous environment outside the cell where it acts as a recognition site for specific chemicals
90
What digestion of carbs takes place in the MOUTH?
- Alpha-Amylase (enzyme) breaks down the alpha-(1,4) links of the starch;
- Randomly breaks at various points of the linear chain
91
What digestion of carbs takes place in the STOMACH?
- NO more carb digestion in the stomach;
| - pH is 1-2 (very acidic) and DENATURES amylase so it no longer works
92
How does carb digestion RESTART in the SMALL INTESTINE?
-Pancreatic juices NEUTRALIZE the pH back up to 7, so amylase enzymes are again ACTIVE
93
How are carbs initially digested in the SMALL INTESTINE?
- Pancreatic alpha-amylase randomly breaks the remaining linear alpha-(1,4) bonds;
- Pancreatic Debranching enzymes breaks the alpha-(1.6) branched bonds
94
How are carbs later digested by the INTESTINAL BRUSH BORDER of the small intestine?
-The brush border is covered with vili that have enzymes present on their surfaces that digest the remaining DIsaccharides
95
Why are the brush border enzymes responsible for disaccharide digestion?
- Alpha-amylase cannot break the down and we cannot ABSORB disaccharides;
- Brush border has the needed hydrolytic enzymes to cleave the disaccharides into individual monosaccharide units
96
What are the disaccharides that make it to the BRUSH BORDER?
- Maltose
- Sucrose
- Lactose
97
What is MALTASE?
- Brush border enzyme for MALTOSE;
| - Breaks the glucose-alpha(1,4)-glucose bonds
98
What is SUCRASE?
- Brush border enzyme for SUCROSE;
| - Breaks the glucose -alpha/beta-(1,2)-fructose bonds
99
What is LACTASE?
- Brush border enzyme for LACTOSE;
| - Breaks the galactose-beta(1,4)-glucose bonds
100
What kind of enzymes are Maltase, Sucrase, and Lactase?
- HYDROLYTIC;
| - Break the disaccharides apart by adding water back into the molecule, and giving one group an H an the other the -OH
101
How are hydrolytic enzymes specific?
- Highly specific to the sugars they can break (typically one sugar, one enzyme);
- Linkage specific (only breaks the types of bonds our enzymes recognize)
102
What can't be digest the glucose-beta(1,4)-glucose of Cellulobiose?
- We don't naturally posses the enzyme in our bodies that recognize the link;
- Only very few microorganisms do
103
How are carbs treated in the BLOOD?
- ONLY monosaccharides can be absorbed;
- Then transported by blood the the LIVER;
- Or may be transported to other cells
104
What happens to carbs when they reach the LIVER?
- Converted to glucose-6-phoshate (or a derivative) immediately;
- P)4 added to glucose at the C6 position from PEP
- G6P then can follow 5 routes in the liver
105
What the 5 possible routes for Glucose-6-phosphate in the liver?
1. Conversion to blood glucose;
2. Conversion to glycogen;
3. Conversion to fatty acids and cholesterol;
4. Break down to CO2 and H20 for energy;
5. Breaks down via Pentose-PO4 pathway
106
How is Glucose-6-Phosphate turned into blood glucose?
- Enzymes remove the PO4 and is sent into the blood to regulate blood levels;
- Highly important to regulate glucose levels for the brain!;
- ONLY occurs in the LIVER
107
How is Glucose-6-Phosphate convert to Glycogen?
- Storage form for SHORT TERM energy supply;
- Glycogen is hydrophilic so it remains within the cells until needed;
- LIMITED amount that can last about a day
108
How is Glucose-6-phosphate turn into fatty acids and cholesterol?
- Converted for LONG TERM energy storage as fatty acids that CANNOT be converted back into glycogen;
- Cholesterol is a structural precursor to steroids that when diet doesn't supply we can produce
109
Why is Glucose-6-Phosphate broken down via the pentose-PO4 pathway?
- To make NADPH = preferred electron donor for synthetic (anabolic) pathways;
- To make Ribose-5-phosphate = 5-carbon sugar
110
How is glucose transported to OTHER CELLS besides the liver?
1. Enter by FACILITATED DIFFUSION (carrier from high to low concentration)
2. Hormonal regulation (Insulin activates the movement of glucose across the membrane)
111
Where is Insulin produced?
- In the BETA cells of the pancreas;
- Initially made in an INACTIVE form (Zymogem);
- When activated will promote the uptake sugar into the cells to drop blood glucose levels
112
What is FASTING blood glucose typically?
-About 75 mg/dL
113
What happens when glucose is INITIALLY ingested?
- Blood glucose levels greatly increase;
| - Release of activated insulin is triggered from the pancreas and sent to the liver
114
What is transient HYPERglycemia?
- The period right after insulin is activated and just starting to uptake glucose from the blood;
- Blood glucose levels are still elevated (hyper) but are lowing to the fasting level
115
What is transient HYPOglycemia?
-Insulin "overshoots" and uptakes TOO MUCH glucose and blood levels drop below the fasting levels
116
How does the body respond to transient HYPOglycemia?
- Glucagon is released and causes the ALPHA pancreatic cells to target the liver and have it break down stored glycogen to glucose-6-phosphate;
- Liver will then remove the PO4 and release the free glucose back into circulation to reach fasting levels again
117
What are diseases associated with sugar absorption and transport?
- Brush border enzyme deficiencies
- Glucose transport abnormalities (Hyper and hypoglycemia)
- Diabetes
118
What happens with Brush Border Enzyme Deficiencies?
- There is a lack of enzymes found on the vili of the intestinal mucosa that break down disaccharides;
- High concentration of disaccharides;
- Osmotic balance disrupted with lots of disacchs. so retains a lot of H2O to balance out;
- Bacterial growth due to them feeding on the sugars
- Lactose intolerance (no lactase to break lactose)
119
What happens with the glucose transport abnormality HYPOglycemia?
- LOW blood glucose concentration;
- Less than 40mg/dL (~1/2 fasting level) = dizzy, shaky, fatigued;
- Either too much INSULIN decreases below normal levels OR not enough functional GLUCAGON to raise levels
120
What happens with the glucose transport abnormality HYPERglycemia?
- High blood glucose levels;
| - Insulin is not effective in regulating the uptake and levels in the blood cannot decrease
121
What is Diabetes?
- Body cannot regulate blood glucose levels and do NOT get enough glucose;
- Means "excess urine"
122
What is Diabetes Insipidus?
-Pituitary disorder characterized by colorless, tasteless urine
123
What is Diabetes Mellitus?
- Urine that is sweet like honey;
- Either juvenile onset (Type 1) or
- Maturity onset (Type 2)
124
What is Juvenile (Type 1) diabetes?
- Insulin dependent;
- BETA cells of the pancreas are damaged and do NOT produce insulin;
- Controlled by diet and insulin
125
What is Maturity Onset (Type 2) diabetes?
- Non-insulin dependent;
- Insulin is produced, but not released properly due to damaged receptors, so there isn't effective binding to the cells;
- Control with diet, exercise and insulin when severe
126
What are the 2 concerns of the liver when dealing with diabetes?
1. maintaining blood glucose levels by releasing limited glycogen stored and synthesizing some glucose from amino acids and fatty acids (gluconeogenesis)
2. obtaining energy for itself through the use of fatty acids
127
What happens to LIPIDS when someone had diabetes?
- Lipids are broken down into ketone bodies that supply the brain and heart with energy or are released as excess acetone;
- "ketone breath";
- Acidosis;
- Dehydration
- Coma
128
What is "Ketone Breath"?
- Breath smells sweet due to the exhalation of acetone from ketones;
- Getting rid of the excess that cannot be used by the body for energy
129
What is Ketoacidosis from the break down of LIPIDS?
- the body fails to adequately regulate ketone production causing such a severe accumulation of keto acids;
- pH of the blood is substantially DECREASED;
- Can be FATAL
130
How does the break down of lipids to ketones cause DEHYDRATION?
- Messes up osmotic balance;
- Excess glucose concentration overflows the renal balance causing high excretion of urine and therefore water loss in attempts to decrease glucose;
- Makes person very thirsty;
- Blood plasma volume does down and causes SHOCK
131
How does the break down of lipids to ketones cause a COMA?
- "Insulin shock" = Death;
| - Level of blood sugar drops so quickly and leads to unconsciousness
132
What is "Insulin Reaction"?
- In a state of HYPOglycemia;
- Condition in a diabetic from an OVERDOSE of insulin that results in a sharp drop in blood glucose;
- Can lead to coma and death
133
What are our sources of glucose for metabolism?
- Dietary carbs;
| - Storage as glycogen in the LIVER and MUSCLES
134
How do we get glucose from our glycogen stores of the LIVER?
- Glycogen converted to glucose-6-phosphate;
- Glucose-6-phosphatase enzyme removes phosphate group (ONLY IN LIVER);
- Lone glucose is released into the blood
135
How do we get glucose from our glycogen stores of the MUSCLES?
- Glycogen converted to glucose-6-phosphate;
| - Then used as energy (does NOT regulate blood levels)
136
What do ALL CELLS immediately do to glucose as soon as it is taken into the cell?
-Immediately activated by phosphorylation or ADDING a PO4
137
How do cell phosphorylate glucose to G6P?
- They use ATP to provide the needed energy and provide the PO4;
- Without ATP energy the reaction would be NON-spontaneous and would not proceed
138
What is the energy of the glucose to G6P reaction?
- Use of ATP makes it overall -4kcall/mol;
- Exergonic and spontaneous;
- Without would be 3.3kcal/mol
139
What is the enzyme used to phosphorylate glucose to G6P?
- Hexokinase;
| - Adds the PO4 and turns the glucose (hexose) into G6P (hexose phosphate)
140
What is the purpose of adding Phosphate to Glucose to make Glucose-6-Phosphate?
1. Activates glucose for a variety of pathways;
2. Prevents glucose from leaving the cell;
3. Helps glucose diffuse into the cells
141
How does making glucose into G6P prevent glucose from LEAVING the cell?
- G6P has a high NEGATIVE charge which keeps in the cell because it repels the negatively charged cell membrane
142
How does making glucose into G6P helps glucose diffuse into the cell?
- Adding the PO4 "disguises" the concentration of glucose within the cell;
- This creates a downhill concentration gradient when there is high glucose outside the cell so it wants to diffuse and create equilibrium of concentration
143
What is the overall reaction of Glycolysis?
- Splitting the sugar;
| - 6 carbon glucose is split into two 3-carbon Pyruvate molecules
144
Why is glycolysis an ancient pathway?
- Anaerobic = require NO oxygen
- Very universal among species from bacteria to humans;
- CANNOT stands alone, but must be couple with other reactions
145
For our pathways, NEGATIVE delta G means...
- Irreversible reaction;
| - Releases so much energy it can't go back
146
For our pathways, delta G from -1 to 1 means...
-Freely reversible
147
For our pathways, POSITIVE delta G means...
-Prefers the reverse direction
148
FIRST step of the Glycolytic Pathway
- Glucose converted to Glucose-6-Phosphate;
- Hexokinase adds PO4 to C6 of glucose by breaking ATP down to ADP;
- IRREVERSIBLE step
149
What is Glucose-6-Phosphate for the various pathways?
- Branch-point compound;
| - Can go various ways and enter different pathways
150
What happens to G6P in the SECOND step of the Glycolytic Pathway?
- Glucose-6-Phosphate converted to Fructose-6-Phosphate
- Isomerization (rearrangement from aldose to ketoses);
- Enzyme = Glucosephosphate Isomerase
- FREELY REVERSIBE step
151
Why is an ENZYME needed to Isomerize G6P (aldose) into Fructose (ketoses) instead of just using alkaline conditions?
- Since this reaction takes place in the body, the change in pH to alkaline conditions needed to cause isomerization in a lab is NOT wanted!!;
- Changes in pH in the body can denature proteins and other problems
152
What happens to Fructose-6-PO4 in the THIRD step of the Glycolytic pathway?
- Fructose-6-PO4 is converted to Fructose-1,6-bisphosphate;
- Another PO4 is added by the breakdown of ATP to ADP;
- Enzyme = Phosphofructokinase (PFK)
- IRREVERSIBLE step;
- COMMITMENT to Glycolysis!
153
Why is another PO4 needed on Fructose-6-PO6 to make Fructose-1,6-bisphosphate?
-Both "halves" of the fructose molecule need to have the PO4 to prevent BOTH from leaving the cell when it is split in to 2 molecules
154
Why is the PFK reaction with Fructose-6-PO4 the commitment to the Glycolysis pathway?
- Removing Fructose-6-PO4 to make Fructose-1,6-bisphosphate pulls on the equilibrium with Glucose-6-PO4;
- More G6P will be converted to Fructose-6-PO4 as it is converted to Fructose-1,6-bisphosphate
155
What happens to Fructose-1,6-bisphosphate in the FOURTH step of the Glycolytic Pathway?
- SPLIT into two 3-carbon molecules = Dihydroxyactone-PO4 (ketone) and Glyceraldehyde-3-PO4 (aldehyde);
- Enzyme = Aldolase
- Reaction PREFERS THE REVERSE (positive delta G)
156
What happens to Dihydroxyacetone-PO4 (DHAP)?
- DHAP is converted to make another molecule of Glyceraldehyde-3-PO4;
- DHAP is a KETONE, but only ALDEHYDES can be used in glycolysis;
- Enzyme = Triosephosphate Isomerase (isomerization)
- Reaction PREFERS THER REVERSE;
- Now everything happens twice!
157
What happens to the 2 Glyceraldehyde-3-PO4 in the FIFTH step of the Glycolytic pathway?
- 2 Glyceraldehyde-3-PO4 are converted to 2 Glycerate-1,3-bisphosphate by oxidation!;
- Aldehyde is oxidized to an acid;
- Enzyme = Glyceraldehyde 3-PO4-dehydrogenase
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How is Glyceraldehyde-3-PO4 oxidized to Glycerate-1,3-bisphosphate in 2 steps?
1. Oxidation of aldehyde to an acid = 2NAD+ are reduced and take on electrons creating 2NADH and H+ (IRREVERSIBLE);
2. Formation of high energy Phosphate bond from phosphate pulled from the cytoplasm (PREFERS the REVERSE)
- Overall reaction is positive and would slightly prefer the reverse
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What happens to Glycerate-1,3-bisphosphate in the SIXTH step of the Glycolytic Pathway?
- 2 Glycerate-1,3-bisphosphate are converted to 2 Glycerate-3-Phosphate by the REMOVAL of a PO4 to make 2ADP INTO 2ATP;
- Substrate -Level Phosphorylation;
- Enzyme = Phosphoglycerate Kinase;
- IRREVERSIBLE step
- ENERGY production!
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What is Substrate-Level Phosphorylation?
-Formation of a high energy Phosphate energy storage compound using ENERGY from the substrate
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What happens to Glycerate-3-Phosphate in the SEVENTH step of the Glycolytic Pathway?
- PO4 group is MOVED from the C3 to the C2 carbon to make 2 Glycerate-2-Phosphate;
- Enzyme = Phosphoglycerate Mutase;
- Prefers the REVERSE
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What happens to Glycerate-2-Phosphate in the EIGHT step of the Glycolytic Pathway?
- 2 Glycerate-2-Phosphate are converted to 2 Phosphoenolpyruvate by the removal of H2O;
- Enzyme = Enolase;
- FREELY REVERSIBLE;
- Now in a much less stable ENOL configuration creating a high energy state
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What happens the Phosphoenolpyruvate (PEP) in the NINTH step of the Glycolytic Pathway?
- 2 PEP are converted to 2 Pyruvate molecules by the removal of PO4;
- Makes ADP into ATP;
- Enzyme = Pyruvate Kinase
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Why does PEP only make one ATP even though there is enough energy to make two?
-The EXCESS energy released when the PO4 bond is broken and a new ATP is made, is used to make up for all the steps in the pathway that would have preferred the reverse, therefore allowing the overall pathway to be NEGATIVE and allowed to proceed
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How many ATP are generated from Glycolysis?
- 4 MADE;
- 2 USED;
- Net = 2 ATP generated per glucose molecule
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How do you know if a reaction RELEASES energy with DIRECT Coupling?
-Large NEGATIVE delta G value
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How do you know if a reaction REQUIRES energy with DIRECT Coupling?
-Large POSITIVE delta G value
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How do you know if a reaction RELEASE energy with ENERGETIC Coupling?
-MAKES ATP
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How do you know if a reaction REQUIRES energy with ENERGETIC Coupling?
-USES ATP
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What reactions RELEASE energy with DIRECT Coupling?
- Hexokinase;
- PFK;
- Phosphoglycerate Kinase;
- Pyruvate kinase
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What reactions REQUIRE energy with DIRECT coupling?
- Aldolase;
- Triosephosphate isomerase
- Phosphoglycerate mutase
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What reactions RELEASE energy with ENERGETIC Coupling?
- Phosphoglycerate kinase;
| - Pyruvate kinase
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What reactions REQUIRE energy with ENERGETIC Coupling?
- Hexokinase;
- PFK;
- Phosphoglycerate kinase
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Why can a reaction release energy in one coupling and require energy in another (EX: PFK)?
-The reaction requires the breakdown of ATP (energetic) to gain the energy needed to make the reaction occur, but it doesn't use all of the energy, so the excess is released (direct)
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What are the main locations of Control Points in metabolic pathways?
- Beginning;
- End;
- or Both;
- Goal is to regulate the RATE of flow from the entrance of raw materials into the pathway to the exit of the products
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What is the main type of reaction that controls metabolic pathways?
- Feedback Inhibition = excess end product blocks the pathway that leads to that product;
- Always ALLOSTERIC!
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How does Feedback Inhibition control metabolic pathways?
- It inhibits the first IRREVERSIBLE step (commitment) after the branch point leading to that product;
- Steps with large NEGATIVE delta G
- Can also target the end product
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Why is Hexokinase controlled in glycolysis even though it is before the branch point? (Glucose to G6P)
-The flow of glucose into the cell needs to be regulate so that cells don't uptake too much glucose and cause them to burst
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How do inhibiting Hexokinase slow the flow of glucose into the cell?
- Preventing the addition of PO4 to glucose to make G6P allows there to be equilibrium of free glucose in and out of the cell;
- The PO4 is added to increase diffusion into the cell, so without it, concentrations will balance and cell won't take on anymore
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How does Glucose-6-PO4 (FEEDBACK) act as the allosteric inhibitor to Hexokinase?
- NEGATIVE allosteric effect;
- Builds up in concentration in the cell and will SLOW hexokinase adding PO4 to glucose in the cell;
- Free glucose concentration in the cell will now build up and equate with the concentration in the blood;
- FEEDBACK
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How is Hexokinase turned back on?
-As the concentration of G6P is used up and decreases in the cell, equilibrium will shift and PO4 will again be added to free glucose "hiding" what is in the cell and increasing diffusion
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How is Hexokinase controlled by Isozymes?
-In the LIVER by Glucokinase
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How does Glucokinase regulated differently that allosteric feedback inhibition?
- It is not lowered by the conc. of G6P;
| - It has a LOWER binding affinity for glucose
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Why is Glucokinase in the liver not inhibited by the conc. of G6P?
- Ability of storage! =
- Liver can store as Glycogen in condensed chains so there is no disruption of osmotic pressure or potential bursting;
- Excess not stored as glycogen is converted to long-term lipid storage
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Why does Glucokinase have a LOWER binding affinity for glucose than Hexokinase?
- Higher KM, Lower binding;
- Will NOT bind to glucose unless the conc. of glucose is high enough to ensure that all other cells have plenty and then it picks up the leftovers;
- Much more efficient than wasting ATP to add/remove PO4 since the liver regulates blood glucose;
- Liver doesn't use glucose for energy
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What is the MAIN reason for both Allosteric control of Hexokinase and Isozyme control with Glucokinase?
-Both regulate glucose entrance INTO the cell!
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How is Pyruvate Kinase controlled? (Split PEP to pyruvate)?
- Allosteric control;
- Large negative delta G reaction;
- INHIBITED by excess ATP that builds up and then binds to cause inhibition;
- INCREASED by AMP (activated by high AMP concentration)
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What is the Energy Balance?
- ATP is HIGH energy;
| - AMP/ADP are LOW energy
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NEGATIVE Allosteric effector of Pyruvate Kinase is...
- ATP;
| - High energy wants to decrease the production of more high energy
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POSITIVE Allosteric effector of Pyruvate Kinase is...
- AMP/ADP;
| - Low energy increases production of needed high energy compounds
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How is PFK controlled?
- COMMITMENT STEP;
- INHIBITED by ATP at the effector site;
- ACTIVATED by ADP/AMP
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How can ATP act as a substrate to PFK and an inhibitor?
- Binds at the ACTIVE site as a SUBSTRATE;
| - Binds at the EFFECTOR site as an Allosteric INHIBITOR (Feedback of the product)
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How does ATP bind PFK at the ACTIVE SITE?
- Binds when ATP conc. is LOW;
- Site has HIGH binding affinity for ATP;
- Low Km (increased binding);
* Binds here when more is needed!
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How does ATP bind PFK at the Allosteric EFFECTOR Site?
- Binds when ATP conc. is HIGH;
- Site has LOW binding affinity for ATP;
- High Km (decreased binding)
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Hexokinase Control
- Allosteric and Isozyme (liver, glucokinase);
- G6P INHIBITS
- NO Activator
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PFK Control
- Feedback INHIBITION of ATP;
| - Allosteric ACTIVATION of AMP/ADP and Fructose-2,6-bisPO4
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Pyruvate Kinase Control
- Allosteric;
- INHIBITED by ATP;
- ACTIVATED by AMP/ADP
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Insulin influence on Glycolysis
- INCREASE [Fructose-2,6-bisPO4]
- INCREASE glycolysis
* Induces uptake of glucose into the cell, and then directs its use
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Glucagon influence of Glycolysis
(Liver)
- DECREASE [Fructose-2,6-bisPO4];
- DECREASE glycolysis
* Makes sure that all glucose is not used up in teh liver but can be sent back into the blood to raise glucose levels
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Epinephrine influence of Glycolysis
(Muscle)
- INCREASES [Fructose-2,6-bisPO4];
- INCREASES glycolysis
* Breakdown of glycogen for muscle-providing energy stores (no blood)
