Chapter 12-3:RNA and Protein Synthesis

What is a gene?

• A gene is a set of DNA instructions that control the synthesis of proteins within the cell.

• This process, called protein synthesis, involves 2 steps: transcription and translation.

How does a gene work?• DNA cannot leave the nucleus, so a copy is

made in the form of a similar nucleic acid called RNA (ribonucleic acid) during transcription. After DNA is used to make RNA, the RNA is then used to make proteins during translation by ribosomes in the cytoplasm.

How is DNA different from RNA?

RNA is a nucleic acid similar to DNA with 3 differences:

1. RNA contains the sugar ribose and DNA contains the sugar deoxyribose

2. RNA is single-stranded, DNA is double-stranded

3. RNA contains uracil instead of thymine. Uracil, like thymine, is a pyrimidine (contains one ring).

How is DNA different from RNA?

Three types of RNA1. messenger RNA

(mRNA):

carries a copy of the information in DNA.

This type of RNA acts as a “messenger” bringing the information in the DNA to the ribosome.

2. ribosomal RNA (rRNA):

this RNA is found with ribosomes.

Recall that ribosomes synthesize proteins.

Ribosomes are made of both proteins and rRNA.

2 subunits

3. transfer RNA (tRNA):

this RNA brings amino acids to the ribosome to be added to the polypeptide chain that is being made at the ribosome.

There is one tRNA for each of the 20 amino acids.

Label this figure on your notes!

Transfer RNA

anticodon

tRNA

Amino acid

Central Dogma of Molecular Biology

• See board

Transcription1. Transcription is the process in which the nucleotide sequence

of DNA is copied, or transcribed into a complementary nucleotide sequence of RNA.

2. DNA is like the “master plan” and RNA is like the “blueprint.” The master plan stays in the nucleus (the office) and the blueprint can be taken to the ribosome (construction site).

3. Because DNA is in the nucleus, transcription occurs in the nucleus of the cell.

4. When transcription is finished, the RNA moves to the cytoplasm. DNA cannot leave the nucleus!!

Transcription5. The enzyme RNA polymerase

is used to make RNA. RNA polymerase:

A. binds to the DNA,

B. separates the DNA, and

C. uses only one strand of DNA as a template to make a complementary RNA strand. RNA Polymerase reads 3’ 5’

Transcription

RNApolymerase

DNARNA

How does RNA look different than DNA?Do RNA and DNA leave the nucleus?

D. Once RNA is made, the RNA detaches from the template strand, leaves the nucleus through nuclear pores, and enters the cytoplasm of the cell

Video Clip: Transcription

Translation

1. RNA is used to make protein in a process called translation.

2. Remember that proteins, a.k.a. polypeptides, are macromolecules made of monomers called amino acids.

3. The Genetic Code

a. In RNA, the nucleotides are read in “words” made of 3 nucleotide “letters”. Each “word” is called a codon and contains the genetic code for one amino acid.

Move from the inside out!

b. The first “word” or start codon is always the same for every protein. It is always AUG. Using the genetic code wheel you can figure out which amino acid a codon represents. What amino acid is associated with the codon AUG?

c. There are a total of 20 different amino acids that can be arranged in different ways to make different proteins.

Methionine

Activity 1

Translation in cytoplasm

Transcription in nucleus

Translation4. During translation, ribosomes decode the mRNA message

(made of nucleotides) to make polypeptide chains (made of amino acids). Ribosomes read 5’ 3’ on the mRNA.

5. Before translation can occur, mRNA must be made from DNA in transcription. Transcription occurs in the nucleus, then the mRNA travels out of the nucleus into the cytoplasm.

6. Translation is done by ribosomes in the cytoplasm. nuclear pore

The steps in translation include:

1. Two subunits of the ribosome attach to the mRNA.

2. Ribosomes read 5’ 3’. As each codon of the mRNA moves through the ribosome, the correct amino acid is brought to the ribosome by tRNA.

3. Each tRNA molecule has a group of three nucleotides called the anticodon. These three nucleotides pair with the nucleotides in the codon. The tRNA molecule also has an amino acid attached.

Transfer RNA

amino acid

Anticodon(3 bases)

4. Peptide bonds form between amino acids to form the polypeptide chain in a process called elongation because it makes the polypeptide chain longer.

– This forms a peptide bond between the amino acids. This is why proteins are called polypeptides.

– The empty tRNA molecule exits the mRNA and is recycled by the cell and can bind another amino acid.

5. The ribosome continues to match the codons in the mRNA with anticodons in tRNA until it reads a codon in the mRNA that says “stop.” A tRNA for “stop” does not carry an amino acid. No peptide bond will form, so the ribosome releases the mRNA and the protein.

6. Polypeptide will start to coil and bend, forming the 3-D shape of proteins (recall the 4 level of protein structure)

Video Clip: Translation

Why are proteins important?Each protein has a specific function within living cells. Some functions of proteins are:1. acting as enzymes, to speed up and regulate

chemical reactions.

2. making pigments that determine flower color in plants

3. determining your blood type.

4. regulating cell growth and development.

Where in the cell does transcription occur?-Nucleus

Where in the cell does translation occur? -Cytoplasm

Chapter 12-4:Mutations

Mutations are changes in the genetic code. They come from mistakes that cells have made in copying their own DNA. If a cell has a mutation, all of its daughter cells will have that same mutation.

How many cells will have the mutation?

Kinds of mutations

Mutations come in many shapes and sizes.

1. Mutations that produce a change in a single gene are called gene mutations.

2. Other mutations produce changes in whole chromosomes (and affect many genes). These mutations are called chromosomal mutations.

1. Point mutations: involve changes in one or a few nucleotides at one point in the DNA sequence.

a. Substitutions: where one base is changed to another. These usually affect only one amino acid.

Gene mutations: affect one gene

Original DNA:

The fat cat ate the rat.

Mutant DNA:

The fat hat ate the rat.(substitution)

Substitution

b. Frameshift mutations (Insertions or Deletions): an extra base is added or removed. These usually affect a large part of the protein. Remember, bases are read in groups of three, but if one base is added or removed, this shifts the “reading frame” of the genetic code and can change all amino acids after the site of the mutation

Insertion

Original DNA:

The fat cat ate the rat.

Mutant DNA:

The fat cat tat eth era t. (insertion)

b. Frameshift mutations (Insertions or Deletions): an extra base is added or removed. These usually affect a large part of the protein. Remember, bases are read in groups of three, but if one base is added or removed, this shifts the “reading frame” of the genetic code and can change all amino acids after the site of the mutation

Deletion

TAG CAT GGA AT

AUC GUA CCU UT

Val Pro Ile

Video Clip: Point Mutations

c. Can change the locations of genes on chromosomes

i. Inversion: reverses the direction of parts of the chromosomes

ii. Translocation: part of one chromosome breaks off and attaches to another.

2. Chromosomal mutations: involve changes in the number or structure of the chromosomes.

Video Clip: Translocation and Inversion

d. Can change the number of copies of some genes

i. Deletion: a part of the chromosome is lost

ii. Duplication: there is an extra copy of part of the chromosome

Video Clip: Duplication and Deletions

  Effects of Mutations

1. Neutral: No effect on protein function

2. Harmful: Cause genetic diseases

3. Beneficial: Plants with extra sets of chromosomes are larger and stronger

4. Any new trait in a population, good or bad, is a result of a mutation.

AUG .