Transcript DNA Structure and Function - Biology at Clermont College

DNA Replication,
Transcription, & Translation
Nestor T. Hilvano, M.D., M.P.H.
(Images Copyright Discover Biology, 5th ed., Singh-Cundy and
Cain, Textbook, 2012.)
Learning Objectives
1. Define key terminologies.
DNA replication, transcription, translation,
codon, anticodon, introns, exons, and nucleotide
2. Compare the structure of DNA and RNA and its
functions.
3. Describe the process of DNA replication.
4. Describe the locations, reactants, and products
of transcription.
5. Describe the locations, reactants, and products
of translation.
6. Describe major types of mutations and their
possible consequences.
Wordstem
•
•
•
•
•
co- together
liga- bound or tied
pleio- more
poly- many
centesis- a puncture
DNA Discovery
• Rosalind Franklin (1950)diffracted helical shape of DNA
when performing X-ray
crystallography using samples
of uniformly oriented strands
created by Maurice Wilkins
• Watson (U.S.) and Crick
(Great Britain)- used quantum
mechanics and x-ray
crystallography (Wilkin and
Franklin) to determine DNA
structure; double helix model;
won the Nobel Prize in
medicine
Rosalind Franklin: July 25, 1920 – April 16, 1958
Figure 10.5B
3 end
5 end
P
HO
5
4
3
2
1
2
A
T
5
P
C
P
G
C
P
P
T
3 end
P
G
P
OH
3
4
1
A
P
5 end
DNA Replication
• Semiconservative; DNA unwound into 2 template strands
• New base pairs (complimentary base pairing)
• Adding at the end of 3’ end of the template toward the 5’ end
(leading strand) or at 5’ end toward the 3’ end (lagging strand=
okazaki fragments)
• DNA polymerase and DNA ligase
Flow of Genetic Information from
DNA to RNA to Protein
• Organism’s genotype – is carried in its sequence
of bases triplet (ex. TAC)
• Transcription is= DNA to mRNA
• Translation is = mRNA to protein (polypeptide)
• Codon – triplets of bases found in mRNA (ex. AUG),
which determines A.A. sequence on a polypeptide,
64 possible codons
- 61 code for amino acids
- start codon= AUG (Methionine)
- 3 stop codons = UAG, UGA, UAA
Transcription
• What is
transcription?
• RNA polymerase
• RNA splicing –
introns (nonsense),
exons (sense)
• Given a DNA template
of TACCGC. What is
the corresponding
codon in mRNA
transcribed?
_________________
RNA polymerase
DNA of gene
Promoter
DNA
initiation
Terminator
DNA
elongation
Area shown
In Figure 10.9A
termination
Growing
RNA
Completed RNA
RNA
polymerase
Exon Intron
Exon
Intron
Exon
DNA
Cap
RNA
transcript
with cap
and tail
Transcription
Addition of cap and tail
Introns removed
Tail
Exons spliced together
mRNA
Coding sequence
Nucleus
Cytoplasm
Figure 10.7_1
DNA
A A
A C
C
G G
C
A
A
A
U U
U G
G
C
G U
U
U U
A
Transcription
RNA
Translation
Codon
Polypeptide
Amino
acid
C
Translation
• Ribosome attaches to mRNA
• tRNA (anticodon)- interprets the message;
delivers amino acids specified by mRNA codons
* 3 stages – initiation, elongation, termination
* Elongation adds amino acids to the polypeptide
chain until a stop codon terminates translation
Met
Met
Large
ribosomal
subunit
Initiator tRNA
P site
UA C
A U G
Start
codon
1
mRNA
Figure 10.13B
A site
U AC
A U G
Small ribosomal
subunit
2
Fig. 17-14
tRNA:
*anti-codon end- pairs
with codon on mRNA
*amino acid on 3` end
* clover leaf shape
base pairs
3
Amino acid
attachment site
5
Hydrogen
bonds
Anticodon
(a) Two-dimensional structure
Amino acid
attachment site
5
3
Hydrogen
bonds
3
Anticodon
(b) Three-dimensional structure
5
Anticodon
(c) Symbol used
in this book
Fig. 17-16b
P site (Peptidyl-tRNA
binding site)
E site
(Exit site)
A site (AminoacyltRNA binding site)
E P A
mRNA
binding site
Large
subunit
Small
subunit
(b) Schematic model showing binding sites
Growing polypeptide
Amino end
Next amino acid
to be added to
polypeptide chain
E
tRNA
3
mRNA
5
Codons
(c) Schematic model with mRNA and tRNA
http://www.youtube.com/watch?v=4PKjF7OumYo&feature=related (go to 4:36)
http://www.youtube.com/watch?v=5bLEDd-PSTQ&feature=related
Mutation
• Change in the nucleotide sequence of DNA; somatic (body cells; passed
on during cell division); germ-line (during gametes development; passed
on to offspring)
• Caused by errors in DNA replication or recombination, or by mutagens
• Point mutation- changes in one base pair of genes (1 gene); substitution,
insertion, or deletion
• Chromosomal mutation- entire section of chromosome, affects multiple
genes; caused by free radicals breaking sugar-phosphate bonds, UC
radiation, and chemical affecting structure of bases.
Normal hemoglobin DNA
C
T
T
mRNA
C
A
T
G
U
A
mRNA
G
A
A
Normal hemoglobin
Figure 10.16A
Mutant hemoglobin DNA
Glu
Sickle-cell hemoglobin
Val
Point Mutation
• Can results to:
a) silent- no change/effect due to redundancy
b) Mis-sense- change of one A.A. (different A.A.
sequence); low efficiency
c) Non-sense- lead to change one A.A. to stop codon;
polypeptide synthesis stop, non-functional protein
d) Frameshift (insertion or deletion)- entire 3 base codon
affected; major difference causing non-functional
proteins
Figure 10.16B
Normal
gene
mRNA
Protein
Nucleotide
substitution
A
U G
A
Met
A U G
A G U U
Lys
A
A G
C
Gly
Ala
Phe
U A G C
U U
Lys
Met
U G G C G
Phe
G C
A
A
Ala
Ser
U Deleted
Nucleotide
deletion
A U G
A
A G
U
G
Ala
Leu
Lys
Met
U G G C
C A
U
His
Inserted
Nucleotide
insertion
A U G
Met
A
A G
Lys
U
U G
Leu
U G G
C G C
Ala
His
Homework
1.
2.
3.
4.
5.
6.
Define terms: nucleotide, translation, transcription,
DNA replication, introns, exons, codons, anticodons,
mutation, point mutation, chromosomal mutation.
Describe the 3 types of RNA: mRNA, tRNA, and rRNA.
Give the bases of CATAAG DNA template, what is the
corresponding bases in DNA replication?
Given the above DNA template in #3 question, what is
the corresponding codons (mRNA) in transcription?
Given AGG codon (mRNA), what is the corresponding
anti-codon (tRNA) in translation?
Describe types of point mutation.