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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?