RNA-UNIT 6 CONT.

StructureTypes of RNATranscription

RNA

=RiboNucleic Acid

STRUCTURE

Polymer Single stranded

Monomers Nucleotides

RNA NUCLEOTIDES

Monomers made of 3 parts each:

Phosphate Group Ribose Sugar 1 of 4 nitrogen bases

C, A, G, and U! U = Uracil No Thymine!

URACIL

Pyrimidine-why? Pairs with adenine

COMPARE RNA TO DNA

3 TYPES OF RNA

1. Messenger RNA (mRNA) “Records” information from the DNA in the

nucleus and transports it out of the nucleus to the ribosomes

3 TYPES OF RNA

2. Transfer RNA (tRNA) Delivers amino acids to site of protein

synthesis (ribosomes)

3. Ribosomal RNA (rRNA) Helps with ribosome structure; function not

entirely understood

We will not go into detail on these second 2 until next week!

WHY IS MRNA IMPORTANT?

DNA is at risk of being damaged if it leaves the nucleus The info in DNA is copied into mRNA mRNA is able to leave nucleus and travel to ribosomes (site of protein synthesis)

WHY IS TRNA IMPORTANT?

It brings amino acids to ribosomes to form protein strand.

HOW DO WE GET MRNA FROM DNA? Transcription

4 Steps (similar to replication)

What is different between transcription and DNA replication?

STEPS OF TRANSCRIPTION

1. DNA is “unzipped” (HELICASE)2. Match correct nucleotides according to base pair rules

*On only one side of the DNA (RNA POLYMERASE)*U’s not T’s!

STEPS OF TRANSCRIPTION

3. Bonding-covalent bonds form between sugar and phosphates

*Why don’t the hydrogen bonds remain?

4. Transcription occurs until a “stop sign” is reached and the mRNA strand is complete

Transcription Animation

GENETIC CODE - TRANSLATION

3 Nitrogen bases represents 1 CODON = 1 AMINO ACID

64 possible codons 3 “stop” codons 61 code for amino acids (20 possibilities) 1 codes to start = AUG = methionine

Code is universal – codons represent the same amino acid in all organisms

CODON DECODER

CODON CHART

Use your codon chart to answer the following:

1. How many different codons code for valine?

2. The codon CGU is for which amino acid?

3. What are the codons for the three “stops”?

4. What are the first 3 amino acids for this strand of mRNA?