Decoding DNA :
Transcription, Translation
and Gene Regulation
How do we get information
from DNA?
DNA is the genetic plan for each cell and a blueprint
for every characteristic in an organism.
The instructions needed to make
proteins are coded in the
nucleotides that make up a gene.
What are some body parts that
contain protein?
Hair
Skin
Nails
Internal organs
PHYSIOLOGY
-Hemoglobin in blood
-Enzymes
Functions of proteins?
Traits such as eye color are
determined by proteins
Proteins are built by instructions in
the DNA.
Some act as enzymes.
Some act as cell membrane
channels.
RNA is involved in making
proteins
RNA- RIBONUCLEIC ACID
DNA
RNA
• consists of a
single strand
• two strands
(double).
• 5 carbon
sugar ribose
• 5 carbon sugar
deoxyribose
• nitrogen
Uracil (U)
base
• nitrogen base
Thymine (T)
3 types of RNA
mRNA – (messenger) copies DNA
rRNA – (ribosomal) –
reads codons on mRNA
tRNA – (transfer) –
places amino acid on
each codon of mRNA
2 Steps of Protein Synthesis
1
2
Steps in making proteins
Step 1 – Transcription- Take a gene
composed of DNA and made (write
down) the mRNA.
Step 2 – Translation- Translate
(Decode) the mRNA into amino acid
sequences.
Step 3- Gene expression- when the
proteins are made.
DNA
mRNA
tRNA
protein
Transcription (Step 1)
Transcription occurs in the nucleus
(eukaryotes) or the cytoplasm (prokaryotes).
Only part of the DNA (a gene) serves a
template.
When the RNA is transcribed the DNA
double helix will reform.
TRANSCRIPTION
Transcription
RNA polymerase (ENZYME) adds
complementary RNA nucleotides
1st RNA polymerase binds to DNA
2nd Elongation unwinds DNA & adds/links
RNA nucleotides.
3rd Reaches a stop signal and is finished
Transcribe mRNA from the DNA
given:
DNA 3’ ATGCTCAA 5’
mRNA 5’ UACGAGUU3’
Give the segment of DNA that this mRNA
was transcribed from.
mRNA: UGAUUC
DNA: ACTAAG
Introns and Exons
Introns- long segments of nucleotides
that have no coding information.
Exons- portions of genes that are
translated. (expressed in proteins).
Introns get cut out of mRNA by
proteins and the Exons are pasted
together.
Genetic Code The genetic code (codons)
used by most organisms to translate
mRNA is nearly universal.
Codons consist of three nucleotide
“words” (three bases)
One codon codes for 1 Amino Acid
The genetic code
There are 20 amino acids
64 possible mRNA codon
combinations
“Start” and “Stop” signals also:
- Start : AUG (Methionine)
- Stop : UAG, UAA, UGA
Each protein is coded for by a gene in
a specific location on DNA
Translation (Step 2)
Takes place in the cytoplasm.
Transfer RNA (tRNA)- a strand of RNA that
carries an amino acid on one end and an
anticodon on the other.
Anticodon - a three-nucleotide sequence of
tRNA that is complementary to a codon on
mRNA.
Protien
Amino
Acid
mRNA
tRNA
Anticodon
Codon
Steps in Translation
Step 1: mRNA leaves nucleus and
enters cytoplasm. The ribosome and
and tRNA carrying amino acid form a
complex.
Determine the Amino Acid Code
that this mRNA codes for.
GUUCAGAACUGU
Valine, Glutamine, Asparagine, Cysteine
What is the maximum number of amino
acids that could be coded for by this
section of mRNA?
4
Gene Regulation and Structure
Gene Regulation and Structure
Not all genes get expressed all the
time. (Translated and transcribed)
If a cell does not need that protein at
the time why waste energy to make it.
In prokaryotic organisms the lac
operon allows bacterium to build
proteins needed for metabolism only
when lactose is present.
MUTATIONS
Changes in an organism’s hereditary
information. Rare but they can occur.
Mutations in gametes (sex cells) can
be passed on the the offspring.
Mutations in body cells only affect the
individual.
Fruit Flies
TYPES OF MUTATIONS
that change genes
Frame shift
Point mutations
Insertion and Deletions
MUTATIONS can be caused by
exposure to ultraviolet radiation
(tanning)
Point Mutation
Only a single nucleotide changes.
Insertion and Deletion
Insertion - a sizable length of
DNA is inserted into a gene.
Deletion - segments of a gene are
lost. Often during Meiosis.
DNA Electrophoresis
A
DNA fingerprint – help determine
how closely related members of a
population are.
The segments of DNA move down
the gel. The smaller pieces move
the furthest down the gel.
Each individual has a unique
pattern of banding.
B
C
D
E
DNA
fingerprinting is
used in forensic
science to
identify victims
or criminals
A human’s genome is all the base
pairs that compose the DNA of the
organism, and their location on th
chromosome.
Human cells contain about
30,000 to 40,000 genes.
Genetic Engineering in
Medicine
Can be used to manufacture human proteins for
use as drugs and to make safer and more
effective vaccines.
Treat human genetic disorders.
Genetic Engineering in
Agriculture
Crops can be genetically engineered to
have favorable characteristics, including
improved yields and resistance to
herbicides and destructive pests.
Genetically engineered growth hormones.
Cloning
DOLLY
GFP (Green Fluorescent Protein)
Comes from the jellyfish Aequorea victoria
In modified forms it has been used to make
biosensors.
Organisms are given this as proof-of-concept
that a gene can be expressed throughout a
given organism.
The big picture:
DNA is coiled into
chromosomes (found
in the nucleus).
DNA is responsible for
inherited
characteristics.
Genes are found on
chromosomes and
consist of DNA, made
of four nitrogen bases.
- mRNA “reads”
DNA and
transcribes the
message for a
protein.
- mRNA makes a
complex with a
ribosome. tRNA
anticodons
match with
mRNA codons
and a protein is
made.