Metabolic Reactions
 Two major types:

Anabolic:
Def – buildup of larger molecules from smaller ones
 Requires energy
 Usually required for cell growth and repair
 Ex: Dehydration synthesis (building of macromolecules
from monomers)


Catabolic:
Def – breakdown of larger molecules into smaller ones
 Releases energy
 Ex: Digestion, hydrolysis (breakdown of
macromolecules)

Enzymes
 Def:
complex molecules (almost always
proteins) that speed up chemical reactions
Lower activation energy (energy needed to get rxn
started)
Considered catalysts (speed up rxn)
 Not consumed during rxn (can be reused)
 Only needed in small amounts

 Very specific to a chemical reaction (or even
sub-steps of a chemical rxn)
 Parts to a enzyme-catalyzed rxn:
Substrate
 Active site

Enzymes
 Substrate:
Def: chemical on which enzyme acts
 Target of an enzyme reaction

 Active site:
Def: the part of the enzyme in which substrate binds
 Specific to each substrate
 Places strain on chemical bonds – which intensifies chemical
reaction

Enzymes
 Environmental

Temp: most enzymes become inactive at 45oC
(113oF)


Heat: enzymes may become denatured (change
shape/function) with extreme heat
Radiation: denaturizing


factors can effect enzymes:
UV: can destroy nucleic acids (and the enzymes working on
them!)
Chemicals/pH: specific environment must be
controlled

Cyanide and carbon monoxide: can destroy respiratory
enzymes
Enzymes
 Some enzymes remain inactive until they bind
with a nonprotein helper
 Two types:

1) Cofactor


Ion of an element (copper, zinc, iron)
2) Coenzyme
Small organic molecule (most are vitamins)
 Ex: coenzyme A (cellular respiration)

Enzyme Intro movie
Energy for Metabolic
Reactions
 Energy: capacity to do work (change or move
matter)



Common forms: heat, light, sound, electricity, mechanical,
chemical
Most metabolic reactions use chemical energy
Chemical energy: energy held in the bonds between atoms
of molecules

Released when bonds are broken (usually starts when heat is
applied)
Energy for Metabolic
Reactions
 ATP:
chief energystoring molecule of
cells
Contains 3 phosphate
groups
 Energy is released
once a phosphate
group is broken off
(and become ADP)

Energy for Metabolic
Reactions
 Cellular respiration:

Process by which food molecules are broken down (using
input of water), making energy (form of ATP) and carbon
dioxide
 Cellular respiration steps (3):



1)Glycolysis: breaks down glucose, occurs in cytoplasm,
forms pyruvate
2) Citric Acid/Krebs cycle: uses pyruvate to make energycontaining electron carrier compounds, occurs mitochondria
3) Electron transport chain: uses electron carrier compounds
from step 2 to drive a series of reactions, creates a LOT of
ATP energy, occurs in cristae of mitochon.
Energy for Metabolic
Reactions
 Two types of cellular

respiration:
Aerobic:
Uses oxygen
 Produces maximum amount of energy/ATP
 Also produces large amount of water


Anaerobic:
Without oxygen use
 Only goes through glycolysis
 Produces very little energy/ATP
 Will produce lactic acid or ethyl alcohol through fermentation
reaction



Lactic acid – causes muscle cramps in humans
Ethyl alcohol – can be used to make alcoholic beverages
Metabolic Pathways
 Def: A sequence of enzyme-controlled
reactions

Ex: DNA replication, protein synthesis
 Rate often determined by regulatory enzyme


Regulatory enzyme: an enzyme responsible by one or more
steps of the pathway
Present in limited quantity
DNA Replication
 DNA:

Consists of nucleotide:




Sugar, nitrogenous bases, phosphate groups
Bases: adenine, thymine, cytosine, guanine
Base pairs: A-T, C-G
Double-stranded molecule made of nucleotides
hydrogen bonded to each other
 DNA replication:


Def: making copy of DNA molecule during S-phase of
Interphase
Mutations: changes in DNA sequence, often caused by issues
during DNA replication
DNA Replication
 Steps of replication:






1) Hydrogen bonds break between base
pairs (which connect strands)
2) DNA pulls apart and unwinds (by an
enzyme called helicase)
3) Nucleotides are exposed
4) DNA polymerase (enzyme) brings in free
nucleotides to pair up with existing
nucleotides
5) Sugar/Phosphate backbone is put
together (by another class of enzymes)
6) DNA proofread for errors (by special class
of enzymes)
7) DNA winds back up
Protein Synthesis
 Cells synthesize/build proteins by using genetic
code (DNA sequence)
 DNA sequence codes for amino acids (which
combine to form proteins)
 Uses DNA, RNA

RNA: ribonucleic acid
Single-stranded
 3 types: m, r, t
 Contains nucleotides


Sugar (ribose), bases (A,U,C,G), phosphate
• U = uracil (nitrogenous base NOT found in DNA)
Protein Synthesis
 Steps:

Transcription:
Takes place in nucleus
 Make RNA (messenger RNA) by using DNA sequence as
a template
 RNA processing:
 Occurs just after transcription (before 2nd step)
 Involves adding nucleotides (or removing!)

Help protect RNA from degradation
 Remove non-coding regions

Protein Synthesis
 Steps:

Translation:
Takes place on ribosomes (in cytoplasm)
 Makes amino acid sequences (polypeptides)
 Uses tRNA (transfer RNA), rRNA (ribosomal) and mRNA

tRNA – transfers amino acid to growing chain by pairing up
with mRNA bases (codons)
 rRNA – found in ribosome (location of translation)
 mRNA – made in transcription, used as a template, 3-base
sections (called codons) pair up with 3-base sections
(anticodons) on tRNA

 Animation