DNA and RNA

Deoxyribonucleic Acid

“the double helix” and

Ribonucleic Acid

The Double Helix

• The structure of DNA was discovered in 1953 by scientists James Watson and Francis Crick.

• Double Helix = “twisted ladder”

Nucleotide

• Basic building block of DNA or RNA

• DNA sugar is Deoxyribose, bases A,T,C,G

• RNA sugar is Ribose, bases A,U,C,G

DNA Base Pairing Rules

• Adenine – Thymine

• Cytosine – Guanine

DNA Replication

• DNA Helicase “unwinds” the helix.

• DNA Polymerase lays down new nucleotides (base pair rules).

• Resulting in two new strands identical with one old and one new backbone each.

Oops! Remember?

• If a mistake is made in replication a MUTATION results.

• Most are caught and repaired during proofreading (CDK and Cyclin “supervisors”).

• Remember: DNA replication takes place during the S phase of the cell cycle (interphase) and has to happen before Cell Division can take place.

RNA Bases Pairing Rules

• Adenine – Uracil

• Cytosine – Guanine

Transcription = making RNA

Copies info from DNA.

3 types of RNA

mRNA= Messenger RNA codon = 3 nucleotides carries “message” from DNA tRNA = Transfer RNA anticodon = 3 nucleotides that pair with codon

rRNA = Ribosomal RNA associates with proteins to form ribosomes.

Comparing DNA to RNA

• DNA• NEVER leaves nucleus• Double Strand• A-T, C-G• Deoxyribose Sugar• ONE KIND• Mistake = MUTATION!• “original blueprints”

• RNA• Made in Nucleolus• Can leave Nucleus• Single Strand• A-U, C-G• Ribose Sugar• 3 KINDS• Codons/anitcodons• “copy for work site”

Practice: ATTCGCCTTACG

• What would the complimentary strand be?

• Is this DNA or RNA?

• What would the transcribed RNA be?