1. Chapter 4: Cellular metabolism

2. Metabolic reactions 2 major types: Anabolism & Catabolism Anabolism
Provides biochemicals required for cell growth & repair
Ex. Cells join many monosaccharides into a chain to form larger molecules of glycogen using an anabolic process called dehydration synthesis
Ex. Links glycerol & fatty acid molecules in fat (adipose) cells to form triglycerides
Ex. Join amino acid molecules to build protein molecules; water molecule forms & a peptide bond joins the two amino acid molecules together
Two bound amino acids form a dipeptide & many joined in a chain form a polypeptide
Polypeptides with specific functions consisting of ~ 100 or more amino acid molecules is called a protein

6. Catabolism
Physiological processes that break larger molecules into smaller ones
Hydrolysis is an example
Decomposes carbohydrates, lipids, and proteins & splits a water molecule in the process
Hydrolysis of a disaccharide like sucrose yields two monosaccharides  glucose & fructose
Hydrolysis occurs during digestion
Breaks down carbohydrates into monosaccharides
Fats into glycerol & fatty acids
Proteins into amino acids
Nucleic acids into nucleotides

7. Control of Metabolic reactions
Metabolic reactions require energy to happen
The temperature in cells is usually too mild to promote the reactions required to support life  enzymes make these reactions possible
Enzymes are almost always proteins & promote chemical reactions within cells by lowering the amount of energy required to start these reactions
Enzymes speed the rates of metabolic reactions (catalysis)
Enzymes are required in small quantities because if they are not completely consumed they can be recycled

8. Each enzyme only acts on a particular chemical (substrate)
Ex. Catalase’s substrate is hydrogen peroxide
During an enzyme –controlled reaction, parts of the enzyme molecule combine with portions of the substrate
Forms an enzyme-substrate complex
The interaction between the molecules distorts or strains the chemical bonds within the substrate  this increases the likelihood that the reaction will occur
Many enzymatic reactions are reversible

9. Factors that alter enzymes
Almost all enzymes are proteins so they can be denatured by exposure to heat, radiation, electricity, certain chemicals or fluids with extreme pH values
Temperature also affects enzymes
Many become inactive at 45 oC and nearly all are denatured at 55 oC
Poisons can denature enzymes
Cyanides interfere with respiratory enzymes, this impairs a cell’s ability to release energy from nutrient molecules

10. Energy for metabolic reactions
Energy is the capacity to change or move matter; the ability to do work
Common forms of energy are heat, light, sound, electrical energy, mechanical energy & chemical energy

11. Release of Chemical Energy
Most metabolic processes use chemical energy
It is held in the bonds between atoms and is released when the bond breaks
Oxidation
Cells burn glucose molecules
This powers the reactions of cellular metabolism
Oxidation inside cells differs from the burning of substances outside cells
‘Burning’ requires a large amount of energy to begin; most of the energy released escapes as heat or light
Enzymes reduce the amount of energy required for oxidation in cells

12. Glycolysis
Enzymes break down glucose in the cytosol into 2 three-carbon pyruvic acid molecules
Does not require O2 so it is the anaerobic phase of cellular respiration
Requires some energy  more is released than consumed
This excess energy is used to synthesize ATP

13. Aerobic Respiration Second phase following glycolysis
Oxygen must be present for this phase to happen
Happens inside the mitochondria & transfers considerably more energy to ATP molecules
When glucose breakdown is complete, CO2 & H2 remains
CO2 diffuses out of the cell as waste
H2 combine with O2 to form water

14. ATP Molecules
For each glucose molecule that is decomposed completely, 38 molecules of ATP can be produced
2 from glycolysis, the rest from aerobic respiration
ATP molecules break apart to release energy for a variety of functions
Muscle contraction, active transport, synthesis of various compounds
ATP molecules that are broken apart becomes an ADP molecule
ADP can convert back into ATP by capturing energy & a phosphate

15. Describe the metabolic pathways of carbohydrates, lipids, & proteins.
What are the products fro each of the metabolic pathways above?
Explain how DNA & RNA store and carry genetic information.
Explain how genetic information controls cellular processes.
How do DNA molecules replicate?

16. RNA Molecules
Messenger RNA (mRNA) – carries the information in a gene’s nucleotide sequence from the nucleus to the cytoplasm
Synthesis of mRNA begins when the enzyme RNA polymerase associates w/ the DNA base sequence at the beginning of a gene
Other enzymes begin to unwind and pull apart the double stranded DNA molecule
This exposes the first portion of a gene
RNA polymerase then moves along this strand
Exposes other portions of the gene & stringing together mRNA from nucleotides
Complimentary to those along the unwound DNA strand

17. Rna molecule EX) If the DNA bases sequence is: A T G C G T A A C A
The complimentary bases in the mRNA molecule will be: U A C G C A U U G U
RNA polymerase somehow knows which of the two DNA strands contains this information
It also knows the correct direction to read DNA
(Just like reading a sentence in a book)

18. RNA molecule
RNA polymerase continues to move along the DNA strand exposing the gene until it gets to a specific DNA base sequence that represents the end of a gene
Called the termination signal
The mRNA molecule is released by RNA polymerase & leaves the DNA
Transcription: process of copying DNA information into the structure of mRNA

19. RNA molecule
Because an amino acid is encoded by a particular sequence of 3 nucleotides in a DNA molecule, the transcribed mRNA represents the complementary set of 3 nucleotides of the amino acid
Codon: a triplet of nucleotides in mRNA that specifies a particular amino acid
Translation: when mRNA molecules associate with ribosomes & act as patterns or templates for the synthesis of protein molecules