RNA and Protein Synthesis

R N A

RIBONUCLEIC ACID

VOCABULARY

1. gene: sequence of DNA that codes for a protein and thus determines a trait

2. mRNA: RNA molecule that carries copies of instructions for the assembly of amino acids into proteins from DNA to the rest of the cell

3. rRNA: type of RNA that makes up the major part of ribosomes

4. tRNA: type of RNA molecule that transfers amino acids to ribosomes during protein synthesis

5. transcription: process in which part of the nucleotide sequence of DNA is copied into a complementary sequence in RNA

6. RNA polymerase: enzyme similar to DNA polymerase that binds to DNA and separates the DNA strands during transcription

7. promoter: region of DNA that indicates to an enzyme where to

bind to make RNA

8. intron: intervening sequence of DNA; does not code for a

protein

9. exon: expressed sequence of DNA; codes for a protein

10. codon: three-nucleotide sequence on messenger RNA that

codes for a single amino acid

11. translation: decoding of a mRNA message into a polypeptide

chain

12. anticodon: group of three bases on a tRNA molecule that are

complementary to an mRNA codon

Types of RNA

mRNA tRNArRNA

TRANSCRIPTION• During transcription, RNA polymerase

binds to DNA and separates the DNA strands. RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of RNA.

• RNA polymerase binds only to regions of DNA known as promoters

have specific base sequences signals in DNA that indicate to the

enzyme where to bind to make RNA.

TRANSCRIPTION

RNA Editing• Many RNA molecules require a bit of editing before they

are ready to go into action.

• The DNA of eukaryotic genes contains sequences of nucleotides, called introns, that are not involved in coding for proteins.

• The DNA sequences that code for proteins are called exons because they are “expressed” in the synthesis of proteins.

• When RNA molecules are formed, both the introns and the exons are copied from the DNA.

• The introns are cut out of RNA molecules while they are still in the nucleus.

• The remaining exons are then spliced back together to form the final mRNA.

Many RNA molecules have sections, called introns, editedout of them before they become functional. The remainingpieces, called exons, are spliced together. Then, a cap andtail are added to form the final RNA molecule.

• Some RNA molecules may be cut and spliced in different ways in different tissues

makes it possible for a single gene to produce

several different forms of RNA. • Introns and exons may also play a role in evolution.

makes it possible for very small changes in DNA

sequences to have dramatic effects in gene

expression

THE GENETIC CODEThe Genetic Code • The language of mRNA instructions• Consist of 20 different amino acids• With 64 possible codons Codon: consist of 3 consecutive nucleotides that specify a specific amino acid (3 bases long) Proteins are made by joining amino acids into long chains called polypeptides

• The property of a protein is determined by the order in which different amino acids are joined together to form polypeptides

TRANSLATIONTranslation

The decoding of an mRNA message into a polypeptide chain (protein) Takes place on ribosomes in the cytoplasm

• Begins when mRNA in the cytoplasm attaches to a ribosome

• Each codon of the mRNA moves through the ribosome

• Proper amino acid is brought into the ribosome by tRNA

• Amino acid is transferred to growing polypeptide chain in the ribosome

• Each tRNA carries only one kind of amino acid

• Each tRNA has 3 unpaired bases called anticodons which arecomplementary to one mRNA codon

• Works like an assembly line

• Polypeptide chain continues to grow until the ribosome reaches a stop codon

• Polypeptide chain is released Protein

TRANSLATION

PROTEIN SYNTHESIS

PROTEINSProtein

Enzymes that catalyze and regulate chemical reactions

Act as microscopic tools to build or operate a component of a living cell

Genes code for proteins that in turn determine genetic traits

MUTATIONSMutation• Changes in the genetic material• Effect on organism

Most effects are neutral Some effects are deadly Some lead to greater genetic

variability in a species• Causes

Random mistakes during DNA replication or RNA transcription Prolonged exposure to excessive radiation or harmful chemicals

• Types of Mutations Point mutation: gene mutations involving changes in one or a few

nucleotides• Occur at a single point in the DNA sequence• Include substitutions, insertions and deletions

Substitution: one base is changed to another Insertions: base is inserted into the DNA sequence Deletion: Base is deleted from the DNA sequence

Frameshift mutation: mutations that shift the “reading” frame of the genetic message by inserting or deleting a nucleotide

• May change every amino acid that follows the point of mutation• Protein may be altered so much that it is unable to perform its normal function• May lead to termination of organism (death)

Chromosomal mutation: involves changes in the number or structure of chromosomes

• May change the locations of genes on chromosomes• DELETIONS: involve the loss or all or part of a chromosome• DUPLICATION: produce extra copies of parts of a chromosome• INVERSION: reverse the direction of parts of a chromosome• TRANSLOCATION: part of one chromosome breaks off and attaches to another

Significance of Mutations

Most are neutral

Some are harmful• Cause genetic disorders• Cause many types of cancer

Some lead to greater genetic variability in a species• Polyploidy: organism has extra sets of chromosomes • Can cause plants to be stronger and larger

TYPES OF MUTATIONSGENE MUTATION

CHROMOSOMAL MUTATIONS