DNA and Protein
Synthesis
Why are you, YOU?
• You are made of
basically four types
of molecules.
• DNA is the molecule
that gives
instructions to your
cells.
• 99.9% of human
DNA is identical.
• Thus, only .1%
makes you, YOU!
Where is my DNA?
DNA is bundled into structures
called chromosomes.
• If the DNA in a person was stretched out it would
reach to the sun and back 600 times. It is an
extremely long molecule that coils really tight.
What is DNA?
• DNA is the genetic information that
determines an organism’s traits.
– DNA produces proteins
• DNA contains the “information for life”
– Complete instructions for manufacturing all
the proteins for an organism
DNA Structure
• Very long molecule!!!
• DNA is a polymer made of repeating
subunits called nucleotides
– Nucleotides have 3 parts:
1. Simple sugar = deoxyribose
2. Phosphate group = 1 atom of phosphorus
+ 4 oxygen atoms
3. Nitrogen base = carbon ring structure that
contains one or more atoms of nitrogen
Nitrogen Bases
•
•
•
•
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
•In DNA there are
four possible
nucleotides, each
containing one of
these four bases.
Purines and Pyrimidines
How do the nitrogen bases
bind?
DNA Bonding Order
• Phosphate group of one nucleotide bonds
to the deoxyribose sugar of an adjacent
nucleotide
– Form the backbone of the chain
• Nitrogen bases bond in complementary
base pairs :
– Adenine (A) bonds with Thymine (T)
– Guanine (G) bonds with Cytosine (C)
DNA Structure
Double Helix
• In 1953, James Watson and Francis
Crick proposed that DNA is made of two
chains of nucleotides joined together by
the nitrogen bases.
– Nitrogen bases are held together by weak
hydrogen bonds
• Shaped like a long zipper that is twisted =
Double Helix
Francis Crick
James Watson
1953
Nobel Prize, 1962
Double Helix
• Rosalind Franklin and Maurice Wilkins
worked together performing X-ray
diffractions of the DNA model
– Photographs revealed that DNA was a
tightly coiled helix
• Chargaff discovered that #A = #T &
#C=#G
DNA Structure
DNA Replication
• DNA replication produces two molecules
from one
• Each strand serves as a pattern to make a
new DNA molecule.
• Begins as an enzyme breaks the hydrogen
bonds between the nitrogen bases.
– Unzips the strand
DNA Replication
• When the DNA needs to be copied so that the
cell can divide the double helix starts to unwind
and unzip down the hydrogen bonds.
Replication Continued
• Nucleotides that are floating free in the
surrounding medium bond to the single
stands by base pairing.
• Another enzyme bonds these new
nucleotides into a chain.
• Each new strand formed is a complement
of one of the original
• DNA Replication Animation
We will now
CREATE a model
of DNA!
Proteins and Enzymes
• DNA produces proteins
• Proteins form key cell structures and
regulate cell functions
• Enzymes are proteins that control
chemical reactions
– Examples:
• Breaking down glucose molecules in cellular
respiration
• Digesting food
• Making spindle fibers during mitosis
Central Dogma of Biology
DNA → RNA → Protein
Transcription
• DNA → RNA
• mRNA, rRNA, tRNA
• Purpose: to send instructions from
nucleus to cytoplasm
Translation
• RNA → Protein
• @ Ribosome
• Purpose: Proteins follow the instructions
and do all the jobs of the cells /
organisms.
• Proteins:
– 20 Amino Acids
– Coded by 3 Nucleotides in RNA, called
codons
Central Dogma
RNA
• RNA is a single
strand
• The simple sugar in
RNA is ribose
• Nitrogen bases in
RNA:
–
–
–
–
Adenine
Guanine
Cytosine
Uracil (bonds with
adenine)
3 Differences between DNA & RNA
DNA
RNA
Double helix
Single strand
Thymine base
Uracil base
Deoxyribose
sugar
Ribose
sugar
Types of RNA
• Messenger RNA (mRNA) = brings information
from the DNA in the nucleus to the cell’s
cytoplasm
• Ribosomal RNA (rRNA) = ribosomes that clamp
onto the mRNA and use its information to
assemble the amino acids in the correct order.
• Transfer RNA (tRNA) = transports amino acids to
the ribosome to be assembled into a protein.
Transcription
• Similar to DNA replication, but the result
is the formation of one single-stranded
RNA molecule (mRNA)
• Process
– Enzyme unzips the DNA molecule
– Free RNA nucleotides pair with
complementary DNA nucleotides
– When pairing is complete, mRNA molecule
breaks away and the DNA rejoins the
original strand
Genetic Code
• Three nucleotides codes for one amino acid
• Each set of nitrogen bases in mRNA represent
and amino acid = CODON
• The order of the nitrogen bases in mRNA will
determine the order of amino acids in a protein
• 64 combinations are possible (43)
• Some codons do not code for amino acids; they
provide instructions for assembling proteins
– Example: Start and Stop signals
Genetic Code Continued
• UAA, UGA, UAG = stop codons
– Protein production ends at this point
• AUG = start codon + amino acid
methionine
• More than one codon can code for the
same amino acid
• Genetic code is universal
– Cell Activities
Translation
• Converts mRNA into the amino acids
that make up proteins
• Translation takes place at the ribosomes
in the cytoplasm
• tRNA molecule attaches to only one type
of amino acid of mRNA
• tRNA makes an anticodon of mRNA
Translation Process
• tRNA brings the first amino acid to the
mRNA strand attached to the ribosome
• Anticodon forms a temporary bond with
the codon of mRNA
• Ribosome slides down the mRNA chain
to the next codon, and tRNA brings
another amino acid
• First amino acid detaches from the
mRNA in the ribosome
• Process continues until a stop codon is
reached
Introns vs. Exons
• Most of DNA is made up of segments that are
NOT expressed
• Introns are segments of genes that are not
expressed (aka DNA Junk)
• Exons are segments of genes that are expressed
• When RNA is made, introns and exons are
copied, then the introns are removed from the
RNA while it is still in the nucleus
• Role of introns in evolution?
– Very small changes in gene expression could have
dramatic effects in gene expression
Genetic Mutations
-Latin meaning “to change”
Genetic Mutations
• Any change in the DNA sequence is called
a mutation.
– Mutations can effect reproductive cells
– Mutations can effect somatic (body) cells
• Example = CANCER
• Types of Mutations:
– Point mutation
– Frameshift mutation
• Insertions or Deletions
– Chromosomal mutation
Point Mutation
• A change in a single base pair in DNA
• Example 1:
– THE DOG BIT THE CAT.
– THE DOG BIT THE CAR.
• Example 2:
– THE DOG BIT THE CAT.
– THE DOG HIT THE CAT.
• Can change the entire structure of a
protein, and effect the shape of the
protein.
Frameshift Mutation
• A single base pair in DNA is deleted or
inserted.
• Every codon after the deleted base would
be different.
• Entire codons can be inserted or deleted
• Example:
– THE DOG BIT THE CAT.
– THE DOB ITT HEC AT.
Chromosomal Mutations
• Five kinds of chromosomal mutations:
– Deletions occur when part of a chromosome is left out.
– Insertions occur when a part of a chromatid breaks off
and attaches to its sister chromatid.
– Inversion occur when part of a chromosome breaks off
and is reinserted backwards.
– Translocation occur when part of one chromosome
breaks off and is added to a different chromosome.
– Nondisjunction – failure of homologous chromosomes
to separate during meiosis
Mutations
Deletion
Duplication
Inversion
Translocation
Causes of Mutations
• Spontaneous:
– Mistake in base pairing during DNA replication or
protein synthesis
– Errors in cell division
• Mutagen – agent that causes DNA change
– High energy radiation
• X-rays, UV light
– Chemicals
• Dioxins, asbestos, benzene, cyanide,
formaldehyde
– High temperatures
Mutagen Video
What is a karyotype?
• Errors from nondisjunction can be
determined by performing a karyotype
• Make a karyotype…
• Cells collected from unborn child
through amniocentesis (skin cells
obtained)
• Blood sample taken from individual
Sample Karyotypes
#1
#2
#3
Sample Karyotypes
#4
Sample Karyotypes