DNA

Transcription Translation

TraitRNA Protein

RNA processing

The ““““Central Dogma””””

What’’’’s Next?

←←←← Contents Transcription and Translation

←←←← Contents Transcription and Translation

Transcription

• DNA code is COPIED asmRNA

– mRNA is the transcript

• Why?

• Location: Nucleus

• Promoter signals where to start

• RNA polymerase binds to

promoter

– Unwinds DNA

– Builds pre-mRNA strand using

DNA as a template strand

Another View of Transcription

The enzyme RNA polymerase opens the DNA strands and

synthesizes an RNA complementary to only one of the DNA strands.

RNA polymerase acts here

Transcription

The decision to transcribe a gene is the most important step in the

control of gene expression. Transcription starts and stops at distinct

sites at the ends of a gene.

DNA mRNA

G--------C

C--------G

A--------U

T--------A

Practice

• DNA: ACGCGCGCGATAATG

• mRNA: UGCGCGCGCUAUUAC

• mRNA processing

– Cut out introns -Junk

– Keep exons- (mRNA that codes)

– Add cap(ribosome recognition) and poly-Atail protection

• Finished mRNA leaves

nucleus & goes to a

ribosome

Alternative Splicing – More Bang for the Buck

• Process where exons of mRNA are reconnected in

multiple ways. Why is this important?

• 23,000 genes

• 100,000 proteins

• How is this possible?!!!!

• SUBWAY analogy

DNA

Transcription Translation

TraitRNA Protein

RNA processing

The ““““Central Dogma””””

Continued….

←←←← Contents Transcription and Translation

←←←← Contents Transcription and Translation

Translation

• Process of makingprotein using themRNA ““““recipe””””

– ““““Translating thecode””””

– 1 gene makes 1polypeptide chain(baby protein)

– Pg. 339

• Location: ribosome

• 3 Sites on ribosome: A, P, E

• Starts w/ a start codon (AUG) on mRNA

• tRNA w/ complimentary anticodon (UAC)

binds to mRNA codon (AUG)

• Each tRNA carries 1 amino acid

• tRNA moves to P site & gives up amino acid to build apolypeptide chain while a new tRNA enters ribosome

– Peptide bonds hold amino acids together (20amino acids)

• E site is where ““““empty”””” tRNA exits

• Stop codon

– Release factor adds

water molecule which

ends translation

Another View of Translation

Many antibiotics

block steps in

translation within

bacterial cells.

Practice

• mRNA: AUGUCAUUUCCA

• tRNA: UACAGUAAAGGU

• Amino acid sequence:

– MET, SER, PHE, PRO

– 64 codons for 20 amino acids

• Using a codon wheel

mRNA tRNA

G--------C

C--------G

A--------U

U--------A

DNA

Deoxyribonucleic Acid

Video- Biologix DNASummary of DNA &Central Dogma 27 min

Mutations?

• Parasitic twins or Siamese twins

– Not a mutation

Mutations

• Change in DNA

• 4 types of effects

• None

• New protein

• Less protein (shorter)

• No protein

Point Mutation

• Most common

• Insert, delete, or change ONE base

• Ex: albinism, Taysach’’’’s Disease, Sickle Cell Anemia– Taysachs- Fat builds up in brain- cant break down

Types of Point Mutations

• Missense

– Affects 1 amino acid

• Nonsense

– Stops early

• Frameshift

– Insertion or deletion

– Shifts sequence

– Affects MANY amino

acids

• Silent

– Codes for same AA

• Practice Worksheet