1. DNA Transcription and Translation: The Central Dogma

2. Protein Synthesis
The DNA inherited by an organism leads to specific traits by directing the synthesis of proteins
DNA directs protein synthesis in two stages, called transcription and translation

3. Transcription and Translation
DNA RNA protein
Transcription: RNA is made, under the direction of DNA
messenger RNA (mRNA)
Translation: protein is made
under the direction of mRNA
Occurs on ribosomes

4. Transcription and Translation

5. Transcription Transcription:DNA- directs synthesis of RNA
RNA synthesis
RNA polymerase pries DNA strands apart & hooks together the RNA nucleotides
Uses the same base- pair rules as DNA, except that RNA has uracil for thymine

6. RNA is single stranded, not double stranded like DNA
RNA is short, only 1 gene long, where DNA is very long and contains many genes
RNA uses the sugar ribose instead of deoxyribose in DNA
RNA uses the base uracil (U) instead of thymine (T) in DNA.
So, in RNA, A  U and C  G
Table 17.1

8. Translation
Translation: RNA directs synthesis of a protein (= a series of amino acids)
Translation:
mRNA
Ribosomes
rRNA
tRNA
Codons (genetic code from DNA to mRNA)

10. Genetic information is encoded as a sequence of base triplets=codons
The Genetic Code
Genetic information is encoded as a sequence of base triplets=codons
DNA
molecule
Gene 1
Gene 2
Gene 3
DNA strand
(template)
TRANSCRIPTION
mRNA
Protein
TRANSLATION
Amino acid A C G T U
Trp
Phe
Gly
Ser
Codon 3 5

11. The Genetic Code Codons: 3 base code for a specific amino acid
There are 20 amino acids; most have more than 1 codon
One codon is used as a START signal: it is at the start of every protein
Universal: in all living organisms

12. The Genetic Code

13. Transfer RNA
Consists of a single RNA strand
Each tRNA has an “anticodon” on one end
tRNA brings the amino acids to the ribosomes
The “anticodon” in the tRNA matches the codon on the mRNA

14. Transfer RNA (tRNA)

15. A summary of transcription and translation in a eukaryotic cell
RNA is transcribed
from a DNA template.
DNA
RNA
polymerase
transcript
RNA PROCESSING
In eukaryotes, the
RNA transcript (pre-
mRNA) is spliced and
modified to produce
mRNA, which moves
from the nucleus to the
cytoplasm.
Exon
Poly-A
RNA transcript
(pre-mRNA)
Intron
NUCLEUS
Cap
FORMATION OF
INITIATION COMPLEX
After leaving the
nucleus, mRNA attaches
to the ribosome.
CYTOPLASM
mRNA
Growing
polypeptide
Ribosomal
subunits
Aminoacyl-tRNA
synthetase
Amino
acid
tRNA
AMINO ACID ACTIVATION
Each amino acid
attaches to its proper tRNA
with the help of a specific
enzyme and ATP.
Activated
amino acid
TRANSLATION
A succession of tRNAs
add their amino acids to
the polypeptide chain
as the mRNA is moved
through the ribosome
one codon at a time.
(When completed, the
polypeptide is released
from the ribosome.)
Anticodon A C U G E
Ribosome 1 5 3
Codon 2 3 4 5
Figure 17.26

16. Mutations
A mismatching of base pairs, at a rate of 1 per 10,000 bases.
DNA polymerase proofreads/repairs accidental mismatched pairs.
Chances of a mutation occurring at any gene is 1 in 100,000
Since the human genome is so large, mutations add up. Each of us inherited 3-4 mutations!

17. Mutation Causes and Rate
Since we have about 6 billion bases of DNA in each cell, every cell in your body contains several mutations.
Most mutations are neutral: have no effect.
Only mutations in cells that become sperm or eggs—are passed on to future generations.
Mutations in other body cells only cause trouble when they cause cancer or related diseases.

18. Point mutations Point mutations = only one base pair is involved.
Point mutations can significantly affect protein structure and function
Point mutations are caused by damage to the DNA from radiation, chemicals or occur spontaneously

19. Mutagens
Physical agents include high-energy radiation like X-rays and ultraviolet light
Chemical mutagens fall into several categories.
Most carcinogens are mutagenic and most mutagens are carcinogenic.

20. Viral Mutagens
Tumor viruses cause cancer in various animals, including humans
About 15% of human cancers are caused by viral infections that disrupt normal control of cell division
All tumor viruses transform cells into cancer cells because the viral nucleic acid joins host cell DNA

21. Point Mutation
The change of a single nucleotide in the DNA’s template strand leads to the production of an abnormal protein
Sickle Cell Anemia is a point mutation

22. Sickle Cell Anemia

23. Types of Point Mutations
Point mutations within a gene can be divided into two general categories
Base-pair substitutions
Base-pair insertions or deletions

24. Insertion and Deletion Mutations