DNA Structure and Analysis
Central Idea of Genetics!
DNA
RNA
Transcription
PROTEIN
Translation
DNA Structure
There are four
kinds of bases
in DNA:
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adenine
guanine
cytosine
thymine
DNA Structure
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Nucleotides join together to form long strands
DNA consists of two strands
Strands twist around each other to form a double helix
Nucleotides are held together by a phosphodiester bond
– Connects the sugar of one nucleotide to the phosphate
of another
• Nucleotide sequence can vary
Phosphodiester bonds
DNA Structure
• DNA consists of two strands joined together by
hydrogen bonds between the base pair
• Base pairs are complementary on opposite
strands
– Adenine only base pairs with thymine
– Guanine only base pairs with cytosine
• Two strands are considered antiparallel
because the polarity of each strand opposite
– Necessary for nitrogen bases to align and form
hydrogen bonds
DNA Double Helix
Polarity of DNA
•Each carbon in the deoxyribose is numbered 1’-5’
• Each strand of nucleotides has a 5’ end
and 3’ end
– The 3’ end used to bond to another nucleotide
– The 5’ end is attached to the phosphate group
of the nucleotide
• A strand of DNA runs from the 5’
3’
DNA structure
http://academic.brooklyn.cuny.edu/biology/bio4fv/page/molecular%20biology/dna-structure.html
DNA Animations
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http://www.pbs.org/wgbh/nova/genome/dna.html#
http://learn.genetics.utah.edu/content/begin/tour/
http://www.johnkyrk.com/DNAanatomy.html
http://www.sumanasinc.com/webcontent/animations/conten
t/DNA_structure.html
Chromosomes and DNA Replication
DNA makes up chromosomes!
DNA and Chromosomes
• In prokaryotic cells, DNA is located in the cytoplasm.
• Most prokaryotes have a single DNA molecule
containing nearly all of the cell’s genetic information.
DNA and Chromosomes
• Many eukaryotes have 1000 times the amount of DNA as
prokaryotes.
• Eukaryotic DNA is located in the cell nucleus inside
chromosomes.
• The number of chromosomes varies widely from one species
to the next.
DNA and Chromosomes
• Chromosome Structure
– Eukaryotic chromosomes contain DNA and protein, tightly packed
together to form chromatin.
– Chromatin consists of DNA tightly coiled around proteins called
histones.
– DNA and histone molecules form nucleosomes.
– Nucleosomes pack together, forming a thick fiber.
DNA Replication
• Necessary to create new
cells!
• Each strand of DNA has all
the information needed to
reconstruct the other half
• Strands are complementary
and can be used to make the
other strand
DNA Replication
• Semiconservative
Replication
– Parent strands
separate and serve
as templates for
new strands
– New DNA molecule
holds one parent
strand and one new
strand
DNA Replication
1. The DNA molecule separates into two strands.
2. Produces two new complementary strands
following the rules of base pairing.
3. Each strand of the double helix of DNA serves as a
template for the new strand.
DNA Replication
New Strand
Original strand
Nitrogen Bases
Growth
Growth
Replication Fork
Replication Fork
DNA Polymerase
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http://www.pbs.org/wgbh/aso/tryit/dna/shockwave.html
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf
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http://www.youtube.com/watch?v=hfZ8o9D1tus
http://www.youtube.com/watch?v=4jtmOZaIvS0
DNA
DNAReplication
Replication
1. Unwinding - Enzymes unzips DNA by breaking
hydrogen bonds. Strands separate at the
replication fork.
Replication Fork
DNA Replication
2. Base Pairing - New complementary
nucleotides are added to the 3’ end to make a
new strand – the new strands are formed in
opposite directions; the enzyme DNA
polymerase attaches nucleotides to produce
new strands.
DNA Replication
3. Joining- DNA polymerase joins the fragments
together. The new DNA strand is proofread
RNA and Protein Synthesis
Genes are coded DNA instructions that control
the production of PROTEINS.
Genetic messages can be decoded by copying
part of the nucleotide sequence from DNA
into RNA.
RNA contains coded information for making
proteins.
Central Idea of Genetics!
DNA
RNA
Transcription
PROTEIN
Translation
RNA
RNA – Ribonucleic Acid
– Composed of a long strain of nucleotides
– Contains sugar, phosphate group, and nitrogen base
RNA
DNA
Ribose sugar
Deoxyribose sugar
Singe-stranded
Doubled-stranded
Uricil
Thymine
RNA
Types:
– Messenger RNA (mRNA) – messenger from DNA
to the rest of the cell
– Ribosomal RNA (rRNA) – make up ribosomes
– Transfer RNA (tRNA) – transfer amino acids to the
ribosomes
Transcription
• The process of making
RNA by copying part of
the DNA sequence into
a complementary RNA
sequence
Transcription
Requires enzyme RNA polymerase
1. RNA Polymerase binds to DNA and separates
strands
2. RNA Polymerase uses DNA as template and
assembles complementary RNA strands
Transcription
Transcription Animations
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http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf
RNA Editing
• The DNA of eukaryotic genes contains
sequences of nucleotides, called introns, that
are not involved in coding for proteins.
• The DNA sequences that code for proteins are
called exons.
• When RNA molecules are formed, introns and
exons are copied from DNA.
RNA Editing
• The introns are
cut out of RNA
molecules.
• The exons are the
spliced together
to form mRNA.
Protein Review
• Proteins are made by joining
– AMINO ACIDS
• Each protein contains a combination of the 20
amino acids
• The function of the protein is determined by
number and sequence of amino acids
• (A polypeptide is a protein!)
Protein 1
Protein 2
Genetic Code
• The genetic code is the “language” of mRNA instructions.
• A codon consists of three consecutive nucleotides on
mRNA that specify a particular amino acid.
Each codon specifies a particular amino acid that
is to be placed on the polypeptide chain.
Genetic Code
RNA Sequence UCGCACGGU
Codon Sequence –
UCG–CAC–GGU
Use the Amino Acid Guide
to determine amino acid –
UCG–CAC–GGU
Amino acid sequence –
UCG–CAC–GGU
Serine – Histidine – Glycine
Translation
• Translation is the decoding of an mRNA
message into a polypeptide chain (protein).
• Translation takes place on ribosomes.
• During translation, the cell uses information
from messenger RNA to produce proteins.
Translation
1. Messenger RNA is transcribed in the nucleus,
and then enters the cytoplasm where it
attaches to a ribosome.
Translation
2. The ribosome “reads” the mRNA codon and
the corresponding amino acid is brought to
the ribosome by the tRNA
Amino Acid
Amino Acid
codon
Translation
3. The ribosome forms bonds between the
amino acids to form the protein
Bond formed
Translation
4. Translation
continues until
the ribosome
reaches a stop
codon on the
mRNA and
releases the
protein
(polypeptide)
The BIG Picture!
Translation Animation
• http://wwwclass.unl.edu/biochem/gp2/m_biology/animation/gene/gene
_a3.html
• http://www.stolaf.edu/people/giannini/flashanimat/molgenet
ics/translation.swf