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Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic mechanism: protein synthesis

Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

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Page 1: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Metabolic Pathways

• What is metabolism?• Two major catabolic pathways:

- glycolysis- citric acid cycle (and

electron transport chain)• One major anabolic mechanism:

protein synthesis

Page 2: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

What is Metabolism?

Metabolism is the sum of all chemical reactions in the body.

Chemical reactions can either create larger molecules (requires energy) or break down large molecules into smaller molecules (releases energy).

The process of breaking down large molecules is called catabolism.

The process of building larger molecules is called anabolism.

Page 3: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Catabolism

Occurs in an orderly manner (not just random degradation)

Breaks down large molecules into smaller molecules

In the process, energy is released

Page 4: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Anabolism

Occurs in an orderly manner Smaller molecules are used to build larger molecules This process requires energy The smaller molecules and energy are obtained from the

catabolism of larger molecules (ie, food)

Page 5: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Catabolic and Anabolic Pathways

Involve specific chemical reactions which occur in an orderly manner (not just random breaking or building of the molecule).

- Each reaction is catalyzed by a specific enzyme.- Other compounds, besides those being metabolized, are required as intermediates in the reaction

- Adenosine Triphosphate (ATP)- Nicotinamide adenine dinucleotide (NAD+)- acetyl CoA

Page 6: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

ATP ATP is the energy currency of the cell The structure of ATP is similar to that of nucleic acids The energy in ATP is “carried” in the phosphate groups

- to convert ADP into ATP requires energy

- the energy is stored as potential energy in the phosphate group bond

- removal of the third phosphate releases that energy

Page 7: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

NAD+

NAD+ can accept a hydrogen ion and become reduced to NADH:

NAD+ + H+ ___> NADH The added hydrogen ion can be carried to and used in other

reactions in the body. Example: NAD+ carries hydrogen ions to the enzymes in

the electron transport chain of the mitochondria, where it plays a role in ATP production.

Page 8: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Acetyl CoA

The enzyme coenzyme A converts acetyl groups (2-carbon structures) into acetyl CoA, which can then be used in catabolic reactions

During the course of acetyl CoA production, energy is released and is used to convert NAD+ to NADH

Page 9: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Glycolysis and the Citric Acid Cycle

NOTE: Your book contains great detail in terms of the structures involved, the enzymes required at each step, and the places where ATP production occurs. DO NOT MEMORIZE THESE DETAILS! Instead, learn the following major features of the catabolic pathways.

Page 10: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Glycolysis

Glycolysis is the breakdown of glucose into CO2, H2O, and energy:

C6H12O6 ----> 6 CO2 + 6 H2O + 38 ATP + heat

Main point: the break down of glucose releases LOTS of energy:

- about 40% in usable form (ATP)

- about 60% as heat Two main steps are involved, occurring in the cytoplasm

of cells (no organelles involved).

Page 11: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

The two main steps of glycolysis

First step: phosphorylation of glucose, and conversion of phosphorylated glucose to diphosphorylated fructose.

- This step requires an “investment” of 2 ATP molecules

- Once you have fructose 1,6-diphosphate, the second step can begin

Second step: breakdown of fructose 1,6-diphosphate into 2 pyruvic acid molecules.

- During these reactions, two NADH are formed

- Four ATP molecules formed

- Pyruvic acid used in aerobic or anaerobic metabolism

Page 12: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Instant Replay

glucose glucose 6-phosphate fructose 1,6- diphosphate

Step one:

ATP ATP

Step two:

fructose 1,6-diphosphate

2 ATP 2 ATP2 NADH

2 pyruvic acid

Page 13: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

What happens to pyruvic acid?

In anaerobic respiration (oxygen absent):

- pyruvic acid is converted to lactic acid

- no further gain in ATP production occurs

- lactic acid goes to the bloodstream, goes to the liver

Page 14: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

What happens to pyruvic acid?

In aerobic respiration (oxygen present):

- pyruvic acid moves from cytoplasm to mitochondria

- pyruvic acid (3 carbons) is converted to acetyl group (2 carbons), producing CO2 in the process

- CO2 is produced from the food we eat, not from the O2 we breath in!

- This reaction is irreversible

- acetyl group is converted to acetyl CoA by coenzyme A

- acetyl CoA is used in the citric acid cycle.

Page 15: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Citric Acid Cycle

Formerly called the Kreb’s cycle Acetyl CoA combines with oxaloacetic acid, forming citric

acid A series of reactions then occurs resulting in:

- one ATP produced

- three NADH produced (goes to electron-transport chain)

- two CO2 molecules produced

Page 16: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Electron-transport Chain The main point: NADH carries H+ ions to the electron-transport

chain, resulting in production of ATP The H+ ions are moved along the transport chain, eventually

accumulating in the outer mitochondrial compartment The H+ ions move back into the inner mitochondrial compartment

via hydrogen channels, which are coupled to ATP production At the end of the transport chain, four hydrogen ions join with

two oxygen molecules to form water:

4 H+ + 2 O2 ----> 2 H2O

In the absence of oxygen, the transport chain stalls (no ATP production)

Page 17: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Catabolism of Fats and Proteins

Fatty acids must be broken down and converted to acetyl CoA, which can then enter the citric acid cycle to generate ATP and NADH (which goes to the electron-transport chain)

For amino acids, the amino groups are removed, and the remainder is broken down to acetyl CoA or pyruvic acid.

Page 18: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Anabolism: Protein Synthesis Recall that the amino acid sequence of proteins is determined by

the nucleic acid base sequence of DNA. But how? Each amino acid is coded for by DNA codons

- a codon is a triplet of bases (ie, CGA codes for alanine)

- since there are four bases and 3 bases/codon, you could conceivably encode 64 amino acids (but you don’t!)

- the code is degenerate; an amino acid can be encoded by more than one codon (ie; CGG also encodes alanine)

- in addition, there are “start” and “stop” codons

Page 19: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Transcription of DNA into RNA

DNA is transcribed into RNA

- two strands of DNA separate

- complementary RNA nucleotides pair with DNA

- RNA nucleotides join to form single stranded mRNA

- mRNA is processed to its final form (splicing) DNA also encodes other forms of RNA

- ribosomal RNA (rRNA); forms ribosomes

- transfer RNA (tRNA); carries amino acids to ribosome, recognizes mRNA codons

Page 20: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Translation of mRNA into protein The mRNA is translated into protein on ribosomes

- ribosomes are composed of rRNA and protein, have two subunits

- mRNA goes to a ribosome

- tRNA has an anticodon, which can combine with complementary codon encoding a specific amino acid

- the tRNA also carries the amino acid specified by its anticodon to the ribosome

- the amino acids join each other (by peptide bonds) Proteins are then modified (shortened, glycocylated,

assembled); called post-translational processing

Page 21: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic

Next Lecture.....

The Integumentary System

Page 22: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 23: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 24: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 25: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 26: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 27: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 28: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 29: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 30: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 31: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 32: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 33: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 34: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic
Page 35: Metabolic Pathways What is metabolism? Two major catabolic pathways: - glycolysis - citric acid cycle (and electron transport chain) One major anabolic