Ribonucleic Acid (RNA) & Protein SynthesisMs. Napolitano & Mrs. HaasCP biology

Think About It!Imagine that we (Ms. Napolitano & Mrs. Haas) are the best bakers ever, and we made a cookbook of delicious cookie recipes. You all would like a copy of our famous chocolate chip cookie recipe, but we only have one cookbook. So, we decide to loan it out to one student at a time. The cookbook can be around from person to person.

1. What are some of the problems with this form of sharing information?

2. What is a more efficient way of getting the recipe to each student?

3. What problems can occur during the copying process?

Recall: DNA Structure

A T

C G

Double helix

Genes

Genes – coded DNA instructions that control the production of proteins within the cell

Part I: RNA Structure

RNA Structure

Long chain of nucleotidesSugar

Phosphate

Nitrogenous base

Differences between DNA & RNA:

In RNA:1. Sugar is ribose (instead of deoxyribose)

2. Single stranded (instead of double stranded)

3. Contains uracil (instead of thymine)

Types of RNA

Messenger RNA (mRNA)Carries copies of DNA instructions out of the nucleus

Ribosomal RNA (rRNA)Make up ribosomes

Transfer RNA (tRNA)Transfers amino acids to the ribosome that are coded in the mRNA

Part II: Protein Synthesis

Protein Synthesis

How proteins are made

Need instructions from DNA

Made of 2 parts:1. Transcription

2. Translation

Transcription

Copying of the DNA sequence

Occurs in the nucleus

Makes a complimentary strand of mRNA

Uses protein RNA PolymeraseSeparates DNA strand

Uses 1 strand of DNA as a template to make mRNA

Starts at a promoter – specific sequence of DNA

RNA Editing

DNA contains segments of intronsNot involved in protein coding

Exons code for proteins

Introns are cut out of the mRNA sequence after transcription

Exons are spliced together

The Genetic Code

The genetic code is read just 3 letters at a time

Codon – 3 consecutive nucleotides that specify for a single amino acid

Ex: Consider the RNA sequence UCGCACGGU

This would be read UCG-CAC-GGU

3 different codons: UCG, CAC, & GGU

Codons represent different amino acidsUCG= serine

CAC = histidine

GGU = glycine

The Genetic Code

Since 4 different bases, 43 = 64 possible codons

Some amino acids have more than one codon choice

AUG is always a “start” codonWhere protein synthesis begins

3 stop codons (end of protein synthesis):1. UGA

2. UAA

3. UAG

Codon Wheel

Codon Chart

Translation

Recall: During transcription, mRNA code was made from DNA, mRNA proofread (introns cut out)

Translation – decoding of mRNA to produce proteins

mRNA moves from the nucleus to the ribosomes

Steps of Translation

1. mRNA attaches to the ribosome.

2. As each codon moves through the ribosome, the proper amino acid is brought in by tRNA.• Each tRNA carries only 1 type of amino acid• tRNA has 3 unpaired bases (anticodon)

that is complementary to mRNA codons

3. Peptide bonds form between amino acids & tRNA is released.

4. Polypeptide chain grows until a stop codon is reached.

Translation

Example of Protein Synthesis

DNA strand: TAACGAGGTACT

Transcription (nucleus): mRNA formed by base pairing

mRNA strand: AUUGCUCCAUGA

Translation: mRNA moves to ribosome, read as codons

AUU-GCU-CCA-UGA

Using codon chart, find amino acids that match

Isoleucine-Alanine-Proline-Stop

this is our new protein!

Part III: Mutations

Mutations

Mutations – changes in genetic material

Point mutations – occur at a single DNA point

Substitutions

Frameshift mutations – shift the reading frame of the genetic message

Dangerous! Could change every following amino acid

Insertions

Deletions

Substitution

Point mutation

One base is changed to a different base

May/may not affect the protein code

Insertions

Frameshift mutation

An extra base pair is (or extra base pairs are) added

Deletions

Frameshift mutation

A base pair is (or base pairs are) removed

Chromosomal Mutations

Chromosomal mutations – changes in the number or structure of chromosomes

Types:Deletion – loss of part of a chromosome

Duplication – extra copies of part of a chromosome

Inversion – reverses the direction of part of the chromosome

Translocation – part of the chromosome breaks off & attaches to another

Chromosomal Mutations

Significance of Mutations

Most mutations do not have an effect on gene expression

Can be very harmful or fatalCystic fibrosis

Sickle cell anemia

Cancer

Source of genetic variabilityResistance to HIV

Polyploidy – extra sets of chromosomesBeneficial in plants – larger and stronger than diploid plants