Download Chapter 4: Cellular metabolism

CHAPTER 4: CELLULAR METABOLISM
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
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
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
• 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
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
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
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
GLYCOLYSIS
• Enzymes break down glucose in the cytosol into 2 three-carbon pyruvic
acid molecules
• Does not require O 2 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
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, CO 2 & H2 remains
• CO2 diffuses out of the cell as waste
• H2 combine with O 2 to form water
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
1. Describe the metabolic pathways of carbohydrates, lipids, & proteins.
2. What are the products fro each of the metabolic pathways above?
3. Explain how DNA & RNA store and carry genetic information.
4. Explain how genetic information controls cellular processes.
5. How do DNA molecules replicate?
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
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)
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
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