RNA and Protein Synthesis

DNA to RNA to Protein

• Focus Questions:

– How does the message coded in the base sequence of DNA eventually create a protein?

– How does the code get out of the nucleus?

– What happens at the ribosome that causes amino acids to eventually join to form a protein?

One Gene One Protein

• Genes: each gene is responsible for the production of a single protein (or part of a protein)– Human DNA contains over a 100,000 different genes

• Proteins: determine the structure and function of an organism– Polypeptides of long chains of amino acids bonded

together by peptide bonds• Ex: Enzymes, Structural proteins

RNA

RNA:– Sugar is ribose instead of

deoxyribose– Has nitrogenous base

URACIL instead of thymine (U instead of T)

• Uracil also would pair with adenine (U-A)

– Only single stranded

3 Types of RNA

1. Messenger RNA: (mRNA): – Copies genetic code

from the DNA inside the nucleus (Transcription)

– Leaves nucleus and goes to ribosome where is the message is read (Translation)

2. Ribosomal RNA: (rRNA)– Form the different parts of

the ribosome

3. Transfer RNA: (tRNA)– Transfers different amino

acids to the ribosomes where they are eventually assembled into protein chains

– Each amino acid is coded for by a different triplet codon on mRNA

– tRNA has an anticodon that will pair up with codon on mRNA

Translation of Genetic Code at Ribosome

3 types of RNA work together

How do Genes Code for Proteins?

Transcription: (Information goes from DNA to mRNA)

• Happens in nucleus

• Enzymes unzip the portion of the DNA to be copied in the middle of the strand

• A single stranded mRNA strand is created from the DNA template – Enzyme RNA polymerase helps this happen

• mRNA leaves nucleus through pores and goes to ribosome

• http://www-class.unl.edu/biochem/gp2/m_biology/animation/gene/gene_a2.html

• If the DNA template strand to be copied is

• ATTGCATG

• What would be the sequence of bases in the mRNA strand?– Remember it has U instead of T

• Triplet Codon: set of 3 nitrogenous bases on a mRNA strand– Each set of 3 can code for a different amino acid– There are 20 different amino acids

There are 64 ways you can combine the four

Nitrogenous bases in sets of 3– AAA, GCC, ATA, ATC, GTA etc.

– Sometimes more than one codon can code for the same amino acid

• Ex: AAA and AAG both code for phenylalanine

– 3 codons signal protein synthesis to stop– 1 codon signals protein synthesis to start

(AUG)

Translation: (from mRNA to protein)

• Occurs at ribosomes• Process of converting information

coded in mRNA into sequence of amino acids

• Involves transfer RNA– Bring specific amino acids to

ribosomes so they can be assembled into proteins

– Has “anticodon” that matches up with each triplet codon on mRNA

– Bottom of tRNA has anticodon triplet

Translation Process:

– 1st triplet codon of mRNa attaches to ribosome

– tRNA carrying amino acid pairs with mRNA codon

– Usually mRNA at start is AUG (“start codon”)

– mRNA slides along ribosome to next codon

– New tRNA with amino acid pairs to mRNA codon

– Amino acids get joined by enzyme by a peptide bond

– Process continues and chain of amino acids form until a stop codon on mRNA is reached

– Protein detached from ribosome

Transcription Video: (really good watch this!!)• http://www.hhmi.org/biointeractive/media/DNAi_transcription_vo1-lg.

mov

Translation Video: (really good watch this!!)• http://www.hhmi.org/biointeractive/media/DNAi_translation_vo1-lg.m

ov

Transcription and Translation Activity:• Game where you make a Protein• http://learn.genetics.utah.edu/content/begin/dna/transcribe/