Transcription, Translation and Mutation

• From DNA to Protein (11.2)• Genetic Changes (11.3)

Answer these questions: What is coded for in DNA? How is it coded?

Proteins The sequence of A, T, G, C

What is the primary structure of a protein? Sequence of amino acids

What are proteins used for? Structure Controlling the biochemistry of an organism

Enzymes, antibodies

From DNA to Protein

DNA cannot leave the nucleus

Protein is made at the ribosomes in the cytoplasm and attached to the rough endoplasmic reticulum

Therefore, a message must be sent from the DNA to the ribosome

From DNA to Protein

The messenger is RNA (mRNA)

DNA Protein: occurs in 2 steps Transcription

Making the coded message (mRNA) Translation

Reading the coded message

How is RNA different from DNA?

RNA DNA

Single-stranded

Sugar = ribose

A, U, G, C

Double-stranded

Sugar = deoxyribose

A, T, G C

3 types of Ribonucleic Acid (RNA) mRNA

Messenger RNA Brings instructions from DNA in the nucleus to the

cytoplasm (where ribosomes are found) rRNA

Ribosomal RNA Part of the ribosome that binds to the mRNA and uses

the instructions to assemble the amino acids in the correct order

tRNA Transfer RNA Delivers the amino acids to the ribosome to be

assembled into a protein

Transcription: DNA to mRNA1. DNA is unzipped2. mRNA is formed, complementary to one of

the strands of DNA RNA polymerase (enzyme) joins the

nucleotides of RNA together

Transcription

3. The mRNA is processed Not all nucleotides in DNA code for making

protein Introns – noncoding sequences Exons – coding sequences

Introns are removed and exons are spliced together

For protection from enzymes in the cytoplasm, the ends of the RNA strand are ‘covered’

5’ GTP cap 3’ poly-A tail

Translation: mRNA to Protein ~20 amino acids and 4 nitrogenous bases (A,

U, G, C) How can 4 bases form a code for all possible

proteins? A group of 3 bases code for 1 amino acid

Each group is called a codon 64 combinations are possible when a sequence of

3 bases is used, therefore there are 64 different mRNA codons

Not all codons code for proteins. UAA = stop AUG = start

More than one codon can code for the same amino acid, but for any one codon, there can only be one amino acid

Translation: mRNA to Protein

MutationsAnswer this question:

How does DNA encode the characteristics of an organism? Each codon in DNA codes for an amino acid (or

start/stop) used to build protein which shapes an organism's characteristics

DNA mRNA Protein Characteristics

A mutation is any change in the genetic code (nucleotide sequence)

Mutations are random

The Causes of Mutations DNA fails to copy accurately

External influences can create mutations Chemicals or radiation break down DNA When the cell repairs the DNA, it might not do a

perfect job of the repair

Types of Mutations Substitution

One base is exchanged for another This will change the codon which could…

Code for a different amino acid and change the protein Code for the same amino acid and do nothing (silent

mutation) Change the code to ‘stop’ and make an incomplete

protein that will probably not function

Insertion Extra base pairs are inserted into a new place in

the DNA

Types of Mutations

Deletion A section of DNA is lost, or deleted

Frameshift Since protein-coding DNA is divided into codons

three bases long, insertions and deletions can ‘shift’ the code

The Effects of Mutations All cells contain DNA = lots of places for a

mutation to occur Somatic mutations occur in non-

reproductive cells and won't be passed onto offspring

The Effects of Mutations Germ line mutations occur in reproductive

cells like sperm and eggs and can be passed to offspring and has large scale effects on evolution The mutation could do nothing The mutation could do something small…

The mutation could have large consequences… http://evolution.berkeley.edu/evolibrary/article/0_0_0/m

utations_06