Warm ups:

1. What are the four bases that make up DNA?

2. What is a mutation?

3. List the different types of mutations…

DNA Transcription & Protein Translation

Today’s Objectives

1. To explain how DNA and RNA code for proteins and determine traits.

2. To investigate and understand common mechanisms of protein synthesis.

Making Proteins

DNA directs the formation of proteins by the ribosomes of the cell.

RNA – Ribonucleic acid. The molecule that carries information from nucleus (DNA) to ribosomes

RNA is different for DNA:

RNA only has one side of the ladder shape RNA’s sugar is ribose (DNA's deoxyribose) RNA has the nucleotide base Uracil (U) in

place of Thymine (RNA also contains the other three bases: A, C and G).

When forming base pairs, C links with G, but A links with U (no T)

Transcription

1. DNA must be copied to messenger RNA (mRNA)What would be the mRNA strand that is copied from the DNA strand below? Remember, RNA has U instead of T

2. mRNA goes from nucleus to the ribosomes in cytoplasm

DNA Sequence GG AA CC UU UU AA

mRNA Sequence

Transcription

3. mRNA complements known as codons– Only 3 nucleotide “letters” long

Transcription – Step I

A C G T A T C G C G T A T G C A T A G C G C A T

Template DNA Strands

Transcription – Step II

A C G T A T C G C G T A U G C A U A G C G C A U

Template DNA is Matched Up with Complementary mRNA Sequences

Transcription – Step III

mRNA leaves nucleus and goes to ribosomes

U G C A U A G C G C A U

A new complementary RNA strand is made (rRNA)

A C G U A U C G C G U A

Protein Translation

1. mRNA leaves the cell nucleus goes to ribosome

2. mRNA code is translated into a transfer RNA (tRNA) code which, in turn, is transferred into a protein sequence.

Protein Translation

3. Each set of 3 mRNA bases (codons) will pair with a complimentary tRNA base triplet (called an anticodon).

4. Each tRNA is specific to an amino acid, as tRNA's are added to the sequence, amino acids are linked together by peptide bonds, eventually forming a protein that is later released by the tRNA.

5. Codon code is specific, but redundant!20 amino acids64 triplet (codon) combinations

Protein translation - example

mRNA codon GAC UUA

Using the mRNA strand we obtained above, we generated the following amino acids

After the processes of transcription and translation are complete, we are left with a protein that consists of the chain: – Aspartic Acid - Leucine

Although our 'protein' is only 2 amino acids in length, proteins normally consist of hundreds or thousands of amino acids.

tRNA structure

3-base code (triplet) is an “anticodon” Protein molecule Attached amino acid that is carried from

cytoplasm to ribosomes

Protein Synthesis

1. Start: Ribosome binds to mRNA at start codon2. Elongation:

– tRNA complexes bind to mRNA codon by forming complementary base pairs with the tRNA anticodon

– The ribosome moves from codon to codon along the mRNA.

– Amino acids are added one by one

3. Release: release factor binds to the stop codon

Exit slip

1. List the three types of RNA?

2. What does RNA stand for?

3. What organelle in the cell is the place for protein production?