BIOCHEMISTRY carbohydrate metabolism

08-11-25

Mouth

Start of the digestion process is always the ?

Salivary α-amylase

hydrolysis of some α-glycosidic linkages;
an enzyme found in human saliva that plays a role in the digestion of carbohydrates, specifically breaking down starch into smaller sugar molecules

Gastric juice

no effect on digestion

Stomach

an organ that helps the conversion of solid food to liquid

Intestine

resumes the enzymatic degradation using the pancreatic digestive enzyme

Pancreatic digestive enzymes

hydrolysis of polysaccharides to disaccharides

Brush border of intestines

disaccharides reaches further hydrolysis when it reaches ?

Intestinal Lining (Villi)

Where products of monosaccharides get absorbed

Salivary enzyme α-amylase

An enzyme that catalyzes the hydrolysis of α-glycosidic linkages of starch and glycogen to produce smaller polysaccharides and disaccharide — maltose

Stomach

Part of the carbohydrate digestion where very little carboydrate is digested
No carbohydrate digestion enzymes present in ?
Salivary amylase gets inactivated because of ? acidity

Stomach acidity

In the stomach, Salivary amylase gets inactivated because of ?

Small intestine

The primary site for the carbohydrate digestion is within the ?
Where Pancreatic α-amylase breaks down polysacccharide chains into disaccharide — maltose

Outer membranes

The final step in carbohydrate digestion occurs on the ? of intestinal mucosal cells

Maltase

hydrolyses maltose to glucose

Sucrase

hydrolyses sucrose to glucose and fructose

Lactase

hydrolyses lactose to glucose and galactose

Bloodstream

Glucose, galactose, and fructose are absorbed into the ? through the intestinal wall

Liver

Galactose and Fructose are converted to products of glucose metabolism in the ?

Galactose and Fructose

are not actually used, usually gets converted to get used by the body

Oxidized to CO2 and H2O (ATP)
Converted to fat
Converted to muscle glycogen

The glucose in the tissues may be:

Blood-sugar level

The proper functions of the body are dependent on precise control of the glucose concentration in the blood.

Glucose concentration

In blood-sugar level, The proper functions of the body are dependent on precise control of the ? in the blood

70-90 mg/100 mL.

The normal fasting level of glucose in the blood is ?

Hypolgycemia

• condition resulting from a lower than the normal blood-sugar level (below 70 mg/100 ml)

• extreme hypoglycemia, usually due to the presence of excessive amounts of insulin, is characterized by general weakness, trembling, drowsiness, headache, profuse perspiration, rapid heart beat, lowered blood pressure and possible loss of consciousness.

• Loss of consciousness is most likely due to the lack of glucose in the brain tissue, which is dependent upon this sugar for its energy.

Hyperglycemia

• higher than the normal level (above 120 mg/100 mL); when the pancreas does not secrete enough insulin

• may temporarily exist as a result of eating a meal rich in carbohydrates.

• extreme hyperglycemia, the renal threshold (160-170 mg/100 mL) is reached and excess glucose is excreted in the urine

Hormones

Besides enzyme inhibition, carbohydrate metabolism may be regulated by ?

Insulin, Glucagon, Epinephrine

Three major hormones control carbohydrate metabolism:

Insulin

51 amino acid polypeptide secreted by the pancreas

Promotes utilization of glucose by cells

The release of insulin is triggered by high blood-glucose levels

Its function is to lower blood glucose levels by enhancing the formation of glycogen from glucose (glycogen synthesis)
Aids in glycogen synthesis

High blood-glucose levels

The release of insulin is triggered by ?

mom Insulin

involves insulin binding to proteins receptors on the outer surfaces of cells which facilitates entry of the glucose into the cells

Glucagon

29 amino acid peptide hormone produced in the pancreas

Released when blood glucose levels are low

Principal function is to increase blood-glucose concentration by speeding up the conversion of glycogen to glucose (glycogenolysis) in the liver

elicits the opposite effects of insulin

Epinephrine

also called adrenaline
Released by the adrenal glands in response to anger, fear, or excitement

Function is similar to glucagon, i.e., stimulates glycogenolysis

Primary target of epinephrine is muscle cells

Promotes energy generation for quick action

Glycogenesis, Glycogenolysis, Gluconeogenesis, Hexose Monophosphate Shunt, Glycolysis, Citric Acid Cycle

Six major metabolic pathways of glucose

Glycolysis

A series of reactions in the cytoplasm which converts glucose (C₆) to two molecules of pyruvate (a C₃ carboxylate), and ATP and NADH are produced.

Also called Embden-Meyerhof pathway, after the scientist who elucidated the pathway.

An anaerobic process; each step takes place without O₂; one of its advantages, the body can obtain energy from glycolysis quickly, without waiting for a supply of O₂ to be carried to the cells.

Occurs in cells lacking mitochondria, e.g., erythrocytes and in certain skeletal muscle cells during intense muscle activity.

Embden-Meyerhof pathway

Glycolysis is also called ?, after the scientist who elucidated the pathway

Phase 1 of Glycolysis

“energy investment phase”
Phosphorylation of glucose and conversion to 2 molecules of glyceraldehyde-3-phosphate; 2 ATP are used in these reactions

Phase 2 of Glycolysis

“energy payoff phase”
Conversion of glyceraldehyde-3-phosphate to pyruvate and coupled formation of 4 molecules of ATP.

Hexokinase

an enzyme that transfers phosphate group
an enzyme that catalyzes the phosphorylation of hexoses, particularly glucose, using ATP

2

How much phosphate does ADP have?

3

How much phosphate does ATP have?

1,3 and 10

In steps of Glycolysis, which steps were irreversible?

-1

In Glycolysis, ATP Change per Glucose in Step 1 and step 3 is ?

+2

In Glycolysis, ATP Change per Glucose in Step 7 and Step 10 is ?

Krebs cycle

In glycolysis, if there is adequate oxygen, an aerobic pathway is followed, and pyruvate enters the ?

Lactic acid

In Glycolysis, If there is insufficient oxygen available, the anaerobic pathway is continued and pyruvate undergoes a series of reactions to produce ?

Lactic acid

is the end-product of glycolysis, and if there not some mechanism for its removal, it would accumulate in the muscle cells & cause muscle “cramps”

Muscle cramps

If there not some mechanism for the removal of lactic acid, it would accumulate in the muscle cells and cause ?

Lactate fermentation

What bacteria uses in the production of yogurt and cheese?

Identical

In glycolysis, Reactions 1 → 9 are ? for glycolysis and alcoholic fermentation for pyruvic acid, the crossroads compound, its metabolic fate depends on the conditions (aerobic or anaerobic) and upon the organism under consideration.

Three common fates for pyruvate

Conversion to acetyl CoA, Conversion to Lactate and Conversion to ethanol. Generated by glycolysis

Aerobic conditions

an environment where oxygen is present and utilized by humans, animals and microorganisms

Anaerobic conditions

an environment where oxygen is present and utilized by (humans, animals and some microorganisms) or (some microorganisms)

Acetyl CoA

When pyruvate is exposed to aerobic conditions in humans animals and microorganisms, it becomes ?

Lactate

When pyruvate is exposed to Anaerobic conditions in humans animals and some microorganisms, it becomes ?

Ethanol

When pyruvate is exposed to Anaerobic conditions in some microorganisms, it becomes ?.
It is how fermentation occurs

adada

Fermentation

a biochemical process by which NADH is oxidized to NAD+ without the need for oxygen

Lactate fermentation, Ethanol fermentation

Two fermentation processes

Lactate fermentation

enzymatic anaerobic reduction of pyruvate to lactate
sole purpose of this process is the conversion of NADH to NAD+
working muscles often produce lactate

Ethanol fermentation

enzymatic anaerobic conversion of pyruvate to ethanol and carbon dioxide
The first step in conversion of pyruvate to ethanol is a decarboxylation reaction to produce acetaldehyde

Decarboxylation

The first step in conversion of pyruvate to ethanol is a ? reaction to produce acetaldehyde

Cori Cycle

Lactate, formed from glucose under anaerobic conditions in muscle cells (glycolysis), is transferred to the liver, where it is reconverted to glucose (gluconeogenesis), which is then transferred back to the muscle cells.

Glycogenesis and Glycogenolysis

Involved in the regulation of blood glucose concentration

Glycogenesis

is the pathway that converts glucose into glycogen.

Hydrolyzed

When theres need for additional blood glucose, glycogen is ? and released into the bloodstream

Glycogenolysis

is the pathway that hydrolyzes glycogen to glucose

Gluconeogenesis

Metabolic pathway by which glucose is synthesized from non-carbohydrate sources:
—The process is not exact opposite of glycolysis
helps maintain normal blood-glucose levels in times of inadequate dietary carbohydrate intake

12-18 hours

Glycogen stores in muscle and liver tissue are depleted with in ? hours from fasting or in even less time from heavy work or strenuous physical actiivity

90%

About ?% of gluconeogenesis takes place in the liver

Non-carbohydrate starting materials for gluconeogenesis:

Pyruvate
Lactate (from muscles and from RBC)
Glycerol (from triacylglycerol hydrolysis)
Certain amino acids (from dietary protein hydrolysis or from muscle protein during starvation)

Citric Acid Cycle

A series of biochemical reactions in which the acetyl portion of acetyl CoA is oxidized to carbon dioxide and ATP and the reduced coenzymes FADH2 and NADH are produced

Mitochondria

The Citric Acid Cycle takes place in the ?

Tricarboxylic acid cycle (TCA) or Krebs Cycle

The Citric Acid Cycle is also known as:

Hans Krebs

Krebs cycle is named after ? who elucidated this pathway

Two important types of reactions of The Citric Acid Cycle

Reduction of NAD+ and FAD to produce NADH and FADH2
Decarboxylation of citric acid to produce carbon dioxide

Steps of Citric Acid Cycle

Mitochondrial matrix

The reactions of the citric acid cycle takes place in the ?, except the dehydrogenase reaction that involves FAD.

acetyl CoA

The “fuel” for the citric acid cycle
obtained from the breakdown of carbohydrates, fats and proteins

Oxidation and reduction

Four of the citric acid cycle reactions involve ?

Riboflavin, Nicotinamide, Pantothenic acid and Thiamin

Four B vitamins are necessary for the proper functioning of the cycle:

Regulation of The Citric Acid Cycle

The rate at which the citric acid cycle operates is controlled by ATP and NADH levels

High

In the regulation of the Citric Acid Cycle, When ATP supply is ?, ATP inhibits citrate synthase (Step 1 of Citric Acid Cycle)

Low

In the regulation of the Citric Acid Cycle, When ATP supply is ?, ADP activates citrate synthase

Isocitrate dehydrogenase

In the regulation of the Citric Acid Cycle, Similarly ADP and NADH control ?

Electron transport chain (ETC)

facilitates the passage of electrons trapped in FADH2 and NADH during citric cycle
is a series of biochemical reactions in which intermediate carriers (protein and non-protein) aid the transfer of electrons and hydrogen ions from NADH and FADH2

Molecular oxygen

The ultimate receiver of electrons

Respiration

The electron transport (respiratory chain) gets its name from the fact that electrons are transported to oxygen absorbed via ?

Inner mitochondrial membrane

In ETC, The enzymes and electron carriers needed for the ETC are located along ?

Complex I, Complex II, Complex III, Complex IV

In ETC, The four protein complexes tightly bound to membrane:

Coenzyme Q and cytochrome c.

In ETC, Two mobile electrons carriers are:

Complex 1: NADH-Coenzyme Q Reductase

Facilitates transfer of electrons from NADH to coenzyme Q

Complex II: Succinate-Coenzyme Q Reductase

Succinate is converted to fumarate by this complex

In the process it generates FADH₂

CoQ is the final recipient of the electrons from FADH₂

Complex III: Coenzyme Q – Cytochrome c Reductase

Several iron-sulfur proteins and cytochromes are electron carriers in this complex

Cytochrome is a heme iron protein in which reversible oxidation of an iron atom occurs

Complex IV: Cytochrome c Oxidase

The electrons flow from cyt c to cyt a to cyt a₃

In the final stage of electron transfer, the electrons from cyt a₃, and hydrogen ion (H⁺) combine with oxygen (O₂) to form water

Oxidative phosphorylation

Process by which ATP is synthesized from ADP and Pᵢ using the energy released in the electron transport chain by coupled reactions

Coupled Reactions

Pairs of biochemical reactions that occur concurrently, where energy released by one reaction is used in the other reaction

• Example: Oxidative phosphorylation and the oxidation reactions of the electron transport chain are coupled systems

Proton pumps

Complexes I,III and IV of ETC chain also serve as "“?” to transfer protons from the matrix side of the inner membrane to the intermembrane space

two electrons

For every ? electrons passed through ETC:
4 protons cross the inner mitochondrial membrane through complex I
4 through complex III; and
2 more through complex IV

basis for ATP synthesis

The high (H+) in the intermembrane space becomes the basis for ?

potential energy

In Oxidative Phosphorylation, The resulting concentration difference (high in the intermembrane space compared to the matrix) constitutes an electrochemical (proton) gradient which is always associated with potential ?.