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

1

5 end 3 end

54

32

1

23

45

P

P P

PP

HO

A T

C G

G C

P P

P

AT

OH

5 end3 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 genePromoterDNA

TerminatorDNA

Area shownIn Figure 10.9A

GrowingRNA

Completed RNA RNApolymerase

Exon Intron Exon Intron ExonDNA

Cap TranscriptionAddition of cap and tail

RNAtranscript with capand tail

Introns removedTail

Exons spliced together

mRNA

Coding sequence Nucleus

Cytoplasm

initiation

elongation

termination

Figure 10.7_1

A

Transcription

RNA

Translation Codon

Polypeptide

Aminoacid

A A C C G G C A A A A

U U G G C C G U UU U

DNA

U

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

Initiator tRNA

1 2mRNA Small ribosomal

subunit

Startcodon

Large ribosomalsubunit

A siteU A CAU C

A U G A U G

P site

Figure 10.13B

Fig. 17-14

Amino acidattachment site

3

5

Hydrogenbonds

Anticodon

(a) Two-dimensional structure

Amino acidattachment site

5

3

Hydrogenbonds

3 5AnticodonAnticodon

(c) Symbol used in this book(b) Three-dimensional structure

tRNA:*anti-codon end- pairswith codon on mRNA *amino acid on 3` end* clover leaf shape base pairs

Fig. 17-16b

P site (Peptidyl-tRNAbinding site) A site (Aminoacyl-

tRNA binding site)E site(Exit site)

mRNAbinding site

Largesubunit

Smallsubunit

(b) Schematic model showing binding sites

Next amino acidto be added topolypeptide chain

Amino end Growing polypeptide

mRNAtRNA

E P A

E

Codons

(c) Schematic model with mRNA and tRNA

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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.

C T T C A T

Normal hemoglobin

Mutant hemoglobin DNA

G A A G U A

Sickle-cell hemoglobin

Normal hemoglobin DNA

Glu Val

mRNA mRNA

Figure 10.16A

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 10.16BNormalgene

Nucleotidesubstitution

Nucleotidedeletion

Nucleotideinsertion

Inserted

Deleted

mRNAProtein Met

Met

Lys Phe

Lys Phe

Ala

Ala

Gly

Ser

A U G A A G U U U G G C G C A

G C G C AAG U U UA U G A A

Met Lys Ala HisLeu

G U UA U G A A G G C G C A U

U

Met Lys Ala HisLeu

G U UA U G A A G G CU G G C

Homework 1. Define terms: nucleotide, translation, transcription,

DNA replication, introns, exons, codons, anticodons, mutation, point mutation, chromosomal mutation.

2. Describe the 3 types of RNA: mRNA, tRNA, and rRNA.

3. Give the bases of CATAAG DNA template, what is the corresponding bases in DNA replication?

4. Given the above DNA template in #3 question, what is the corresponding codons (mRNA) in transcription?

5. Given AGG codon (mRNA), what is the corresponding anti-codon (tRNA) in translation?

6. Describe types of point mutation.