RNA, Transcription, and the Genetic Code

RNARNA = ribonucleic acid

- Nucleic acid similar to DNA but with several differences

DNA RNANumber of strands

2 1

Type of sugar Deoxyribose RiboseNucleotides Used

A, G, C, and T A, G, C, and U (Uracil)

*Uracil replaces Thymine in RNA and base pairs with Adenine!

RNATypes of RNA:

1. Messenger RNA (mRNA)- carries DNA message out of

nucleus to ribosomes

2. Ribosomal RNA (rRNA)- found in ribosomes

3. Transfer RNA (tRNA)- contain anti-codons used in

translation, brings amino acid to ribosome

TranscriptionTranscription = process of making an mRNA strand from DNA

- Similar to replication but remember, RNA is single stranded not double stranded.

- Enzyme involved is called RNA polymerase.

TranscriptionSteps:

1. Initiation- RNA polymerase binds to

promoter region of DNA strand.- Promoter = region of DNA that

signals the start of a gene

2. Elongation- RNA polymerase creates a 5’ to 3’

mRNA strand using DNA as a template.

TranscriptionSteps:

3. Termination- RNA polymerase reaches end of DNA

sequence that codes for gene (Termination sequence) and releases mRNA into nucleus.

Transcription Animation

Transcription

RNA SplicingBefore mRNA strand is sent out of the nucleus. Non-coding parts need to be taken out through RNA splicing.

Introns= Non-coding segments, taken out

Exons= Coding segments, spliced together mRNA Splicing Vide

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RNA Splicing

The Genetic Code* Proteins are made when mRNA molecule travels out of nucleus to cytoplasm to ribosomes.

• Proteins are mode by joining amino acids together into long chains called polypeptides.

• Order of amino acids determines the properties of the protein.

The Genetic Code• A, G, C, and U bases of RNA

form a “language” called the Genetic Code.

• It is universalCodon = every three letters on an mRNA strand.

The Genetic Code* Genetic code is degenerate since 64 different combinations of letter code for only 20 different amino acids. That means that most amino acids can be specified by more than one codon.Important codons are start and stop:

Start = AUGStop = UAA, UGA, UAG

The Genetic Code