Name: ______Per. _____

Unit 7 Protein Synthesis & Mutation

Protein Synthesis

The formation of proteins based on information in DNA and carried out by RNA.

(Gene expression)

Flow of Genetic Information

►  DNA “unzips”

►  Transcription- makes RNA

►  Translation- makes protein

►  Protein

Compare and Contrast DNA & RNA

DNA / Both / RNA

3 Types of RNA

1.  Messenger RNA (mRNA)

2.  Ribosomal RNA (rRNA)

3.  Transfer RNA (tRNA)

1.  Messenger RNA (mRNA)- Carries the instructions from DNA

2.  Ribosomal RNA (rRNA)- Make up Ribosomes

3.  Transfer RNA (tRNA)- Transfers amino acids to the ribosome to make a protein Has 3 nucleotides on one end (anticodon) and the corresponding amino acid on the other (codon).

How do the ribosomes get instructions from DNA?

The Definition of Transcription:

Transcription

•  The process by which RNA is made from part of the DNA sequence that codes for a protein (gene)

•  Transcription is taking the blueprint DNA and making a copy in the form of RNA

•  This RNA blueprint will be used to assemble proteins

Steps of Transcription

  1. An enzyme unzips the DNA molecule at the region of the gene that is being transcribed
  2. Free RNA nucleotides form base pairs with their complementary nucleotides on the DNA strand
  3. mRNA threads away and the DNA strand rejoins
  4. mRNA leaves the nucleus and goes to the cytoplasm (ribosome)

•  Codon is a group of 3 nucleotides in mRNA that specifies an amino acid (building blocks of protein)

•  Think of the codon as the drawings on the blueprint for the genetic code

Translation Definition

•  Use the codon of mRNA to specify the sequence of amino acids to build a protein

•  It is time for the Blueprint (DNA-mRNA) to be read

•  The Blueprint (mRNA) is sent to the construction site (Ribosome)

•  Decoding of the genetic instructions

Steps of Translation

  1. mRNA arrives at the Ribosome
  2. tRNA Anti-codons are complementary to the mRNA codons
  3. tRNA picks up an amino acid
  4. tRNA delivers the amino acid to the ribosome
  5. Amino acids are assembled into polypeptide chains, to form protein, held together with peptide bonds

When the mRNA is first transcribed, there are long sequences of nucleotides that are not required for the synthesis of the protein called introns. The DNA sequences that code for the protein are known as exons. Introns are edited out (cut out) of the mRNA before it leaves the nucleus and the remaining exons are spliced together to form the final mRNA

How to use the Codon Wheel:

Take the codon from mRNA

Ex: AUC

The 1st letter will be in the center and work your way out with the 2nd and 3rd.

So AUC would code for the Amino Acid Isoleucine or ISO

NEVER USE tRNA on the Codon Chart!!!

Color the following diagram

Mutations

A mutation is a __change in the DNA sequence_. Although many mutations are harmful, some mutations are __silent__, and others may be very _beneficial__ to an organism. There are two categories of mutations:

A. Chromosomal Mutations

A chromosomal mutation involves a change in the structure of the entire chromosome or a change in the total _number of chromosomes. Does not alter individual genes. These errors generally occur during meiosis or mitosis_.

B. Gene Mutations

A gene mutation is a change in one gene on an individual chromosome. This may result in a change in only one nucleotide or many nucleotides making up that gene might be altered. The incidence of gene mutations is relatively low due to the action of enzymes that proofread the DNA sequence after replication. There are two types of gene mutations:

1. Point Mutations – This is a change in one or just a few _nucleotides_, but the total number of nucleotides in the gene is not changed. This might have no effect, or change one amino acid. Therefore, the resulting __protein_ may or may not be altered.

Example:

THE DOG BIT THE CAT

THE DOG BIT THE CAR

As you can see, changing a single letter changes the meaning of the sentence.

2. Frameshift Mutations – This involves the addition or deletion of a nucleotide. When a nucleotide is inserted or deleted, this shifts the reading of the remainder of the codons; therefore, the translation of the remainder of the mRNA is altered. This will usually result in tremendous changes in the __amino acid__ chain and completed protein.

Example:

THE DOG BIT THE CAT

Deleting the G

THE DOB ITT HEC AT

–  This mutation would cause nearly every amino acid after the deletion to be changed.