CHAPTER 12
DNA and RNA
12-1 DNA
What is a gene?
A sequence of DNA that codes for a protein that
determines a trait
What is DNA?
Deoxyribonucleic acid
DNA is the chemical structure that makes up a
gene
DNA DISCOVERIES
 Griffith
 Studied pneumonia- harmless strain + harmful strain
 Killed harmful strain and mixed with harmless
 Mice still got sick!
 Conclusion: disease-causing ability was inherited
 Transformation: process by which one strain of
bacteria is changed by a gene or genes into another
DNA DISCOVERIES
 But HOW was it inherited?
 Avery
 Made extract (“juice”)from harmful bacteria
 Treated it to kill certain macromolecules
 Transformation still happened
 Treated it to kill DNA
 No transformation
 Conclusion: nucleic acid (DNA!) responsible for
transformation
DNA DISCOVERIES
 Hershey and Chase
 Studied viruses
 Bacteriophage: virus that infects bacteria
 Made up of protein coat and DNA
 which carries genetic material?
 Conclusion: DNA does!
4 CRITERIA FOR A GENE:
1. must be able to store info. and be able to
carry it from one generation to the next
2. must be strong and stable so it doesn’t
break down
3. must be easily copied
4. must be able to mutate- variation allows for
adaptation to occur
DNA STRUCTURE
 What are the monomers of nucleic acids?
 Nucleotides
 Nucleotides made up of 3 parts:
 5 C sugar
 Phosphate group
 Nitrogenous bases
 Adenine (A)
 Guanine (G)
 Cytosine (C)
 Thymine (T)
STRUCTURAL DISCOVERIES
Chargoff- base pairing
A = T and C = G
Rosalind Franklin- x-ray diffraction
showed “x” shape pattern
Watson and Crick
Double helix (“twisted ladder”)
H bonds between bases
DNA ORIGAMI!
 http://www.yourgenome.org/teachers/ origami.shtml
12-2 CHROMOSOMES AND DNA
REPLICATION
Where is our DNA?
Eukaryotes- nucleus
multiple chromosomes
Prokaryotes- cytoplasm
usually 1 chromosome
DNA STRUCTURE
VERY long
Ex: E. Coli has 1 chromosome
Like fitting 300m of rope in a backpack
Nucleus of a human cell has ~1 meter of DNA
How does it fit?
CHROMOSOME STRUCTURE
 Chromosomes made up of…
 Chromatin: DNA coiled around protein (histones)
 Form a nucleosome- continue folding DNA in nucleus
(coils and supercoils)
DNA REPLICATION
Replication: process by which a cell duplicates
it’s DNA
WHY do we replicate DNA?
Mitosis
Meiosis
DNA REPLICATION
Step 1: two strands separate
Enzyme helicase “unzips” the double helix
break H bonds
Creates 2 replication forks
DNA REPLICATION
Step 2: base pairing creates complimentary
strands
Half old/half new
Enzyme DNA polymerase joins individual
nucleotides forming a polymer
proofreading
DNA REPLICATION
 http://www.youtube.com/watch?v=zdDkiRw1PdU
12-3 RNA AND PROTEIN SYNTHESIS
 Gene: a sequence of DNA that codes for proteins that
determine a trait
 What does protein synthesis mean?
 Making proteins!
 “code” = nucleotide sequence
 Must first turn DNA into RNA
RNA
 Ribonucleic acid
 RNA Structure:
 Single stranded
 Ribose sugar
 Phosphate group
 Nitrogenous bases
 Uracil in place of thymine (U in place of T)
3 T YPES OF RNA
 ALL involved in protein synthesis
 1. Messenger RNA (mRNA)
 Carries copies of instructions to make proteins from
DNA to rest of cell
 2. Ribosomal RNA (rRNA)
 Make up ribosomes
 3. Transfer RNA (tRNA)
 Transfers amino acids to ribosomes during protein
synthesis
PROTEIN SYNTHESIS
Involves transcription and translation
Transcription: copying DNA sequence into RNA
sequence
Translation: using mRNA to code for a protein
TRANSCRIPTION
 DNA separated into 2 strands
 RNA polymerase (enzyme)-uses each strand as a
template to build complementary RNA strand
 (similar to DNA polymerase)
 Promoter region- specific sequence of bases that
tells where to start building RNA strand
RNA EDITING
 RNA polymerase also
proofreads + corrects
mistakes
 Exons: nucleotides that
code for proteins
 “express proteins”
 Introns: nucleotides NOT
involved in protein
synthesis
 These are “cut” out
THE GENETIC “CODE”
 What are the monomers of proteins?
 Amino acids! (aa)
 RNA has 4 possible bases (A, U, C and G)
 3 bases = codon: code for a specific aa
 aa are added together to make a protein polymer
 “start” and “stop” codons
TRANSLATION
 Ribosomes “read” the code for the
protein
 “Expression”
 1. mRNA attaches to ribosome
 2. codons code for an aa
 tRNA brings aa to ribosome- add to
chain
 Peptide bonds
 Anticodon- part of tRNA- complimentary
to mRNA codon
 3. continue until “stop” codon
TRANSLATION
PROTEIN SYNTHESIS- SUMMARY
PROTEIN SYNTHESIS
 http://www.youtube.com/watch?v=NJxobgkPEAo
ROLES OF DNA AND RNA
DNA: like a master plan
stay safe in the nucleus
RNA: like a blue print copy
disposable
GENES AND PROTEINS
 What does protein have to do with
traits?
 Genes: code for protein that determines a
trait!
 Proteins are microscopic tools that
build parts of living things
 What we look like
 Many proteins are enzymes- catalyze
chemical reactions
 How we function
VOCABULARY QUIZ REVIEW
 The type of RNA that carries instructions to make
proteins from DNA to the rest of the cell
 Messenger RNA (mRNA)
 A sequence of DNA that codes for a protein that
determines a trait
 Gene
 The type of protein that DNA coils around to make
chromatin
 Histone
 The enzyme used to create the new strand of DNA
during replication
 DNA polymerase
VOCABULARY QUIZ REVIEW
 A sequence of nucleotides that are involved in
protein synthesis
 Exon
 A 3 base sequence of nucleotides that code for an
amino acid
 Codon
 A 3 base sequence of nucleotides found on tRNA that
are complimentary to a codon
 Anticodon
 A region of DNA that signals RNA polymerase to start
building the RNA strand
 Promoter region
VOCABULARY QUIZ REVIEW
 This is the process of copying a DNA sequence into an
RNA sequence
 Transcription
 This is the process of using mRNA to code for a protein
 Translation
 This is the process where one strain of bacteria is
changed into another strain by altering a gene or genes
 Transformation
 The rule that, in DNA, cytosine can only bond to guanine
and adenine can only bond to thymine
 Complimentary base pairing
12-4 MUTATIONS
Mutations: changes in genetic material
Gene mutations: changes in single gene
Chromosomal mutations: changes in whole
chromosomes
GENE MUTATIONS
 Point mutations: involve 1 or a
few nucleotides
 Effect 1 aa
 Types: Substitutions,
insertions, deletions
 Frameshift mutations: a shift
in the entire reading frame
 Effects all aa
 Protein may be unusable
CHROMOSOMAL MUTATIONS
 Types:
 Deletion- loss of all/part of a chromosome
 Duplication- extra copies of a chromosome
 Inversion- reverse direction of the chromosome
 Translocation- part of a chromosome breaks off and
joins a different one
SIGNIFICANCE OF MUTATIONS
 Most are harmless/neutral
 Some change proteins structure/expression - cause
damage
 Cancer and other disorders
 Some are beneficial
 Ex: polyploidy plants- have extra sets of
chromosomes- are usually stronger
12-5 GENE REGULATION
 Genes are “turned on and off” as needed
 Expression: when a gene is turned on, and the
protein is coded for
 Not all genes expressed at once
 Prokaryotes and eukaryotes regulate differently
LAC OPERON EXAMPLE
 Prokaryote gene regulation
 Operon: a group of genes working together
 Regulatory sites (aka: operator): site where proteins
bind to regulate transcription
 Lac operon genes- used by E. coli to break down
lactose for food
 When lactose is present, gene turned “on”
 When no lactose present, protein binds to operator,
turning gene “off”
EUKARYOTE GENE REGULATION
More complex- usually no operons
TATA box- sequence of nucleotides tells RNA
polymerase where to go and what to express
Only express what is needed
G
T
A
T
A
G
C
G
A
T
DEVELOPMENT AND DIFFERENTIATION
 Differentiation: when cells become specialized in
structure and function
 Hox genes controls differentiation in cells, starting in
the embryo
HOX GENE MANIPULATIONS
 Hox genes can be manipulated
 Ex: gene for antenna replaced with gene for leg
 You get a leg on the fly’s face!
 Common ancestry= ability to manipulate across
species
 Ex: gene for mouse eye + gene for fly leg = eye on fly’s leg
REAL LIFE GENE REGULATION ISSUETERATOMA
 http://www.youtube.com/watch?v=jpk61xc8KF4