RNA and Protein Synthesis

Chapter 12, section 3

The Structure of RNA“Central Dogma” of Biology:DNA is “read” by RNA which then travels to the ribosomes to make proteins.

DNA RNA Proteins

The Structure of RNA RNA, like DNA, is made up of

nucleotides However, there are 4 major

differences between DNA and RNA: RNA has ribose instead of

deoxyribose RNA has uracil instead of thymine RNA is single-stranded instead of

double-stranded RNA is able to leave the nucleus.

3 Types of RNA Messenger RNA (mRNA) – carries the

message from the DNA to the ribosomes Ribosomal RNA (rRNA) – make up part

of the structure of a ribosome Transfer RNA (tRNA) – transfers amino

acids to the ribosomes

Transcription DNA mRNA Making RNA from DNA (in the

nucleus) RNA polymerase binds to DNA

and begins building a complementary strand of mRNA A will now pair with U, T still pairs

with A C and G still pair with each other

Why mRNA? mRNA can leave the nucleus!

Transcription

The Genetic Code DNA and RNA are “read” 3 bases at

a time A codon is a 3 base sequence that

codes (“signals”) for a specific amino acid There are 64 possible codons (3 letter

combinations) Proteins are made of amino acids There are 20 different amino acids

Practice Transcription… DNA – AGC TCC GAT GCA TAC TTG CCA mRNA– UCG AGG CUA CGU AUG AAC GGU

DNA – GCC AGT GCT TAC GAA CTG AGT mRNA– CGG UCA CGA AUG CUU GAC UCA

The Genetic Code RNA sequence:

UCGAGGCUA Separate into codons:

UCG-AGG-CUA Identify the “signaled” amino

acids: Serine-Arginine-Leucine

The Genetic Code

Translation mRNA Proteins Making of proteins using the

instructions from the mRNA message (“translating the code”)

Occurs at the ribosomes

Translation1. Following transcription, mRNA

leaves the nucleus and enters the cytoplasm.

2. The mRNA attaches to the ribosome

3. The tRNA brings the proper amino acid to the ribosome

Anticodon – sequence of bases on the tRNA that pair with the mRNA

Translation4. The amino acids form a peptide

bond to hold them together The next amino acid is brought in and is attached

5. This continues until the ribosome reaches a stop codon

6. The completed protein (polypeptide chain) is then released

Translation

Mutations Changes in the DNA sequence

that affect genetic information Gene mutations – result from

changes in a single gene. A gene carries the “recipe” for a single protein.

Chromosomal mutations – involve changes in whole chromosomes

Body-cell v. Sex-cell Mutation Somatic cell mutations are not passed on to the next generation. Mutations that occur in sex cells are passed on to the organism’s offspring and will be present in every cell of the offspring.

Mutations

Gene Mutations Point mutations – a mutation

that occurs at a single point (only 1 nitrogen base) Substitution – a single nucleotide is

substituted for another one (A instead of G)

Frameshift mutations– a mutation that occurs when a nucleotide is inserted or deleted Insertion – a nucleotide is added Deletion – a nucleotide is removed

Gene Mutations Insertions and deletions cause

frameshift mutations because they shift the “reading frame” of the genetic message.

Gene Mutations