Chapter 8: DNA and RNA

1
Chapter 8DNA and RNA

• Section 8-3
• RNA

2
Introductory Question

• How is the genetic code decoded?
• What does it say?

3
RNA

• RNA ribonucleic acid
• Molecule used to decode the genetic information
  found in DNA
• Carries out the instruction coded in DNA

4
RNA vs DNA
DNA RNA
Deoxyribose is 5-carbon sugar Ribose is 5-carbon sugar
Double stranded Single stranded
Contains bases A, T, G, C Contains bases A, U (uracil), G, C
U bonds to A
5
Transcription

• Process of making RNA from DNA template
• Part of DNA sequence is transcribed (copied) into
  RNA
• RNA polymerase carries out transcription by
  binding directly to DNA and matching nucleotides
  one at a time
• AACTGT on DNA
• UUGACA on RNA

6
(No Transcript)
7
Animations

• http//www.fed.cuhk.edu.hk/johnson/teaching/genet
  ics/animations/transcription.htm
• http//www.johnkyrk.com/DNAtranscription.html

8
Transcription

• Transcription begins at a special start
  sequence on the DNA (promoter) and ends at a
  stop sequence
• Usually, one gene is transcribed at a time

9
Why go through the trouble?

• By using RNA as an intermediary, the cell is able
  to copy the same DNA sequence over and over if
  needed, allowing the DNA to stay intact.

10
Forms of RNA

• Messenger RNA (mRNA)
• Carries copies of the instructions to make a
  protein
• Acts as messenger between DNA and the rest of
  the cell

11
Forms of RNA

• Ribosomal RNA (rRNA)
• Remember that proteins are assembled at ribosomes
• Ribosomes are composed of several dozen proteins
  and a unit of rRNA

12
Forms of RNA

• Transfer RNA (tRNA)
• Used to transfer one amino acid after another to
  the ribosome when proteins are assembled

13
The Genetic Code

• There are 20 different amino acids that make up
  all proteins
• The genetic code the language of instructions
  in DNA and RNA
• Nucleotides in mRNA are read in groups of three

14
Codons

• A group of 3 nucleotides in mRNA is called a
  codon and specifies a particular amino acid
• Example mRNA AAACACGGU
• read as AAA CAC GGU
• Lysine Histidine Glycine

15
Codons

• More than one codon for each amino acid
• Example UUU and UUC phenylalanine
• AUG is called the start or initiation codon
  (codes for methionine, which is usually the first
  amino acid in a protein)
• The three stop or termination codons are UAA,
  UAG, and UGA

16
Translation

• Process in which nucleotide sequence in mRNA is
  decoded into a series of amino acids to make a
  protein (all forms of RNA)
• mRNA decoded at ribosome, where tRNA brings amino
  acids needed (tRNA anticodon)
• P. 185 mRNA gets read at ribosome and
  translated into an amino acid sequence

17
Genes and Proteins

• A gene is a section of DNA the directs the
  synthesis of a protein
• DNA transcribed into mRNA
• mRNA translated into an amino acid sequence to
  form a protein at a ribosome
• Proteins control traits