Protein Synthesis &

Mutations

Chapter 13

The Central Dogma of Biology:

Protein Synthesis

RNA Structure:1. It is a nucleic acid.2. It is made of monomers called nucleotides3. There are two differences between a DNA

& an RNA nucleotide:- RNA has ribose instead of

deoxyribose- RNA has the base Uracil

instead of Thymine- Adenine will pair with Uracil

(Uracil is a pyrimidine)

Protein Synthesis

Types of RNA:1. Messenger RNA (mRNA)

- carries the info from DNA to the ribosome - contains “codons” that code for individual amino acids

2. Ribosomal RNA (rRNA)- a component of the ribosome

3. Transfer RNA (tRNA)- “Transfers” the info on the mRNA to

an amino acid sequence (protein).- contains “anticodons” that

complement the codons on mRNA.

Protein Synthesis

What is transcription?It is the process of making an RNA copy from a DNA template.

- All forms of RNA are made using this process.

- The process is similar to replication.

Protein Synthesis

The Steps of Transcription:1. Initiation:

RNA polymerase binds to a location on the DNA called a promoter.

- Promoters signal the beginning of a gene.

- RNA polymerase has the ability to unzip the DNA.

Protein Synthesis

The Steps of Transcription:2. Elongation:

RNA polymerase makes a complementary RNA strand from one of the exposed DNA strands.

- This DNA strand is called the “template strand.” (sense strand)

Protein Synthesis

The Steps of Replication:

3. Termination:

RNA polymerase comes across a DNA sequence called a “terminator” and stops the transcription process.

Protein Synthesis

Eukaryotic mRNA Transcripts must be edited.

1. The original mRNA contains sequences known as introns & exons.

Introns = sequences that do not code for anything. Exons = sequences that actually code for a protein.

2. The introns are cut out and the exons are spliced together.

3. A cap sequence & a tail sequence are added and the mRNA is ready to go.

Protein Synthesis

The Genetic Code:1. The sequence of the DNA bases “codes” for the

individual amino acids in a protein.2. This code is copied on to an mRNA strand.3. The mRNA code:

- 3 mRNA bases in a row are called a codon & each codes for a particular amino acid.

4. Because there are 4 RNA bases, there are 64 different

3-base combinations (104 = 64).- One combination is known as the “start

codon” (AUG). This marks the beginning of the protein.

- Three of them are “stop codons” (UAA, UAG, UGA). These codons do not code for any amino acids, thus signaling the end of the protein.

Protein Synthesis

What is the amino acid sequence from the following mRNA sequence?

AUGGUCGAUAAACCACGCCUGUGAMet-Val-Asp-Lys-Pro-Arg-Leu

Protein Synthesis

What is Translation?Process in which a ribosome reads the mRNA & makes a protein (polypeptide).

Ribosome Structure:1. Has two subunits: small & large2. Large subunit has two sites:

p site (polypeptide site) a site (amino acid site)

Protein Synthesis

Translation Animation

Protein Synthesis

What is a mutation?Any kind of change to the base sequence of either DNA or RNA.

- Mutations cause the amino acid sequence to be incorrect.

- An incorrect amino acid sequence usually causes the protein to be nonfunctional or it gives the protein new functions.

Mutations

1. Gene Mutations (a.k.a. point mutations)These affect a particular gene only.A. Substitution – replace one base with another. - affects only one amino acid in the protein. - May not even cause a problem (silent mutation). B. Insertion – a new base is placed in the sequence; this alters the reading frame & every amino acid after the mutation is altered.C. Deletion – a base is removed & every amino acid after this mutation is altered.

Insertions & deletions are called frameshift mutations.

Types of Mutations

2. Chromosomal Mutations – affect whole chromosomesA. Deletion – part of the chromosome disappearsB. Duplication – part of the chromosome is copied.C. Inversion – the sequence of genes on the chromosome is partially flipped.D. Insertion – part of one chromosome is removed an placed onto a different chromosomeE. Translocation – parts of two chromosomes are clipped off and they switch places.

Types of Mutations