DNA Structure & Function
Chapter 13 & 14
outline
• History of dna
• Structure and function of dna
• Dna replication
– Molecular replication
– Gene replication
dna
– Was known as a chemical in cells by the end
of the nineteenth century
– Has the capacity to store genetic information
– Can be copied and passed from generation to
generation
– Located in the nucleus of cells
– “blueprint” of life
Watson & crick
Rosalind franklin
Nucleic acids
• Information storage molecules
• Directions for building proteins
• Found in nuclei of eukaryotes
• Two forms
– Deoxyribonucleic acid
– Ribonucleic acid
• Polymers of nucleotides
Nucleotide
• 5 Carbon sugar
– Deoxyribose
– ribose
• Phosphate group
– Po4-
• Nitrogenous base
– Accepts H+
– Adenine
– Guanine
– Cytosine
– Thymine (DNA only)
– Uracil (RNA only)
• Form polynucleotides aka dna strand
DNA structure
• Sugar-phosphate backbone
– Deoxyribose sugar
– Covalent bonds
• Complementary Nucleotides
– Pyrimidine
• Thymine (T)
• Cytosine (c)
– Purine
• Adenine (a)
• Guanine (g)
• Double helix
– Hydrogen bonds
• Information storage
Nucleotide Molecular structure
Dna nitrogenous Bases
Information stored in Sequence of
Nucleotides
RNA Structure
• Sugar-phosphate backbone
• Ribose sugar
• Complementary Nucleotides
– Uracil (u)
– Cytosine (c)
– Adenine (a)
– Guanine (g)
• RNA has uracil in place of thymine
• Single strand
• Information transfer and translation
Rna nucleotides
Sugar phosphate backbone
Complementary base Pair Rule
G-C A-T A-U in RNA
Double helix
Double helix
• A-T
• C-G
• Hydrogen
bonds
Dna Replication
• When a cell or organism reproduces, a
complete set of genetic instructions must
pass from one generation to the next
• Replication of entire strands- occurs
during interphase
• Replication is semiconservative
DNA Replication
• Template mechanism
• DNA strand is unwound and double helix is separated
• Single strand replicated via base pair rule
– Base pairs- hydrogen bonds
– Sugar phosphate backbone- Covalent bonds
• Many enzymes & proteins involved
– Dna polymerases
• Origins of replication
– Multiple replication sites
• 2 Daughter strand created
DNA Replication is
Semiconservative
DNA Replication Uses
Complementary Base Pair Rule
Many Enzymes Involved
DNA Molecule Replication
– Begins at
specific sites on
a double helix
– Proceeds in
both directions
– Multiple sites of
replication
DNA Molecule Replication
Produces 2 Daughter Strands
Dna function
– stores genetic information
– Instructions for all life and life processes
• Contains protein building instructions
– Uses specific code built into sequence of
nucleotides
terminology
• Gene
– Sequence of nucleotides that is the unit of
hereditary information
– Ie. A recipe
• Genome
– The sum of an individuals genes
Genes Located on Chromosomes
Genetic code
• Genes have nucleotide code for building
proteins
– Proteins are made of amino acids
• The set of rules giving the correspondence
between nucleotides of nucleic acids and
amino acids of proteins
Genetic code
• Codon aka Triplet
Code
– Sets of 3 nucleotides
Genetic Code
• Each codon
represents an amino
acid
• Code is redundant
• Specific Start & stop
codons
• Code is universal to
life
Why are proteins so important?
remember…..
Protein Types
• Structural
• Storage
• Contractile
• Transport
• Defense
• Signal
• Enzymes
• The one gene–one protein hypothesis
states that the function of an individual
gene is to dictate the production of a
specific protein
Junk DNA
Gene Expression
• How dna’s instructions are carried out
• Code in gene is copied and used to build
proteins
• Involves multiple steps
– transcription
– translation
• Uses dna and rna
• 2 problems must be overcome in order for
DNA to work
In Animal Cell… DNA is Isolated in
the Nucleus
Protein Building Stuctures in
cytoplasm
Problem #1
• Genetic information aka “building
instructions” in the nucleus
• Ribosomes aka “builders” outside the
nucleus
– Solution= transcription
Problem #2
• How do we build proteins from dna?
• Dna is a sequence of ??
&
Proteins are a sequence ??
•The information, or “language,” in DNA is ultimately
translated into the language of proteins
Transcription vs translation
• Transcription
• Translation
– Transcription occurs in the nucleus
– Translation occurs in the cytoplasm
– Are the processes whereby genes control the
structures and activities of cells
Transcription
• Converts Dna to rna
– Results in strand of messenger rna (template)
– Uses Complementary base pair rule
• Region of copying unwinds & then rewinds after mrna is
complete
• 3 steps of transcription
– Initiation
• Promoter- specific base sequence at beginnings of genes
• Aka Start codon
– Elongation
• Copies information
– Termination
• Terminator base sequence at ends of genes
• Aka Stop codon
Transcription
Messenger RNA (mRNA)
• RNA Template of DNA
• Single strand of nucleotides
• Uses Uracil instead of Thyamine
• Moves from inside nucleus to cytoplasm
• MRNA is processed before it leaves the
nucleus
Genes are made of Introns & exons
– Exons
• Segments of DNA that
code for AA
– Introns
• Sections of nucleotides
that do not code for AA
• Regulatory function
mRNA Is Processed
• MRNA is spliced (cut & paste)
– Introns removed
• MRNA ends are capped
mRNA Is Spliced
Rna processing
DNA
Transcription
Addition of cap and tail
RNA
transcript
with cap
Introns removed Tail
and tail
Exons spliced together
mRNA
Coding sequence
Nucleus
Cytoplasm
Translation
– Is the conversion from
the nucleic acid
(nucleotide) language
to the protein
language (amino acid)
– Converts mRNA to
protein
Translation- players
• Messenger rna (mrna)
• Transfer rna (trna)
• Ribosomal rna (Rrna)
Transfer RNA (tRNA)
• Molecular translators
• Converts nucleotide code into amino acid
language
• Carries specific to amino acid
• Matches amino acid codon in mRNA using
anticodon
• Recycled after each use
Transfer rna
Ribosomal RNA
– Site of protein
synthesis tRNA
binding sites
– Are made up of two
protein subunits Large P site A site
subunit
– Made up of
ribosomal RNA
(rRNA) mRNA
P A
– Holds mRNA & binding
site
tRNA
Small
subunit
ribosome
Translation Steps
• Initiation
• Elongation
• Termination
• Initiation
Initiation
– mRNA binds Met
with ribosome Initiator
(rRNA) tRNA
components mRNA
– tRNA translates
codons to amino
Small ribosomal
acids with subunit Large ribosomal
subunit
anticodon
– Starts at A site
P site
promoter codon Initiation
Elongation
• Elongation
– Codon Polypeptide
Amino acid
recognition P site
– Peptide bond mRNA
Anticodon
A site
formation Codons
Codon recognition
– Translocation of Elongation
tRNA
Peptide bond formati
New peptide
mRNA bond
movement
Translocation
Termination
– Elongation reaches stop codon
– rRNA, tRNA & mRNA complex disassembles
Mutagen
• physical or chemical agents that induce
change in nucleotide sequence of dna
(aka Mutation)
• Physical
– Radiation
– X-ray, uv light
• Chemical
– carcinogens
• Viral
Mutagen
Mutation
• Mutation
– A change in the nucleotide sequence of a
nucleic acid
• Point mutations
– “switch” nucleotide
• frame shift mutations
– Insertion- add extra nucleotides
– Deletions- delete nucleotide
Mutation
• Good or bad
• Beneficial/ adaptive
• deleterious
– They are the
source of the rich
diversity of genes
in the living world
– They contribute
to the process of
evolution by
natural selection
Viruses sit on the fence between life and non-
life
– They exhibit some
but not all
characteristics of
living organisms
Viruses
• Nucleic acid in protein coat
– DNA or RNA viruses
• Reliant on host for reproduction
• Typically Host specific
– Bacteriophages
– Plant viruses
– Animal viruses
• Hiv, aids
Virus Structure
Viruses
Virus “Takeover”
Virus Transfer
ex West Nile Virus
Vector
RNA Virus
• Infects host with RNA segment
• Replicated in the cytoplasm
• Hepatitis C
• Dangue fever
• West Nile virus
• Polio
• Common cold
• Measles
• Rabies Hantevirus
• Influenza
RNA Virus
ex Rabies
DNA Virus
• Infect host with DNA strand
• Enters nucleus and is replicated by host
• Smallpox
• Herpes
• HPV
DNA Virus
HPV Replication
HIV
• Retrovirus
• RNA template to synthesize a segment of
DNA
• DNA segments migrates into nucleus &
inserts into Host DNA= Provirus
– Will be duplicated with host DNA
– Will be transcribed into RNA
– Will be translated into viral proteins
• http://www.whfreeman.com/kuby/content/a
nm/kb03an01.htm
AIDS
• Acquired Immunedeficiency Syndrome
• Viral proteins kills white blood cells
• Leaves host vulnerable to disease- kills
• anti-HIV drugs
– Interfere with virus reproduction
– Inhibits reverse transcriptase- AZT
– Inhibit protease- ie protein production
Chapter 16
Biotechnology
Cell Differentiation
Embryonic vs. Adult Stem Cells
Stem Cells
DNA Technology
• Gene identification & manipulation
• Gene identification- ex cancer gene,
depression gene, DNA fingerprinting,
paternity tests
• Recombinant DNA technology
– Genetically modified organisms (GMO)
– Transgenic organisms
DNA Fingerprinting
Biotechnology
• Biotechnology-
manipulation
– Use Bacteria genome
• Simpler
• Smaller
• Easy to manipulate
Biotechnology
Bacteria
• Circular DNA
• Plasmid
– Accessory Rings of
DNA
Recombinant DNA
• DNA that contains DNA from two sources
Recombinant DNA
• Humulin- bacteria
• GM foods
– Insect resistant
– Antifreeze
– Growth rate
– Reduce decay
Recombinant DNA Techniques
• Bacteria genetic material- plasmid
• Splice DNA using restriction enzymes
– Enzymes that “cut” DNA at specific nucleotide
sequences
• Restriction site
• restriction fragment length polymorphism
(RFLP)
– Segments of spliced DNA
Paternity Test
GMO Vs. Hybrid
• Genetic modification • Hybrid-Genetics. The
involves the isolation, offspring of
manipulation and genetically dissimilar
reintroduction of DNA parents or stock,
into cells or model especially the
organisms, usually to offspring produced by
express a protein breeding plants or
animals of different
varieties, species, or
races.
US leading world in GM
production
Top GMO
Labeling the United
• Currently
• In the EU, if a food
contains or consists States requires no
labeling discussing the
of genetically
genetic modifications
modified organisms made to the food we buy
(GMOs), or contains
ingredients produced
from GMOs, this must
be indicated on the
label.
So What?
• Pollination possible between transgenic
and landrace plants
• Uncontrollable
• Create more plants that are capable of
deterring certain bugs or viruses
• Evolution of viruses or bugs compromises
the non-transgenic species
• Like using antibiotics when not sick
Ethics
http://www.storewars.org/flash/index.html