Central Dogma of Molecular Biology

Gene Expression

• How does a cell control the timing and choice of synthesizing a particular protein?

• A gene is expressed when it is transcribed (a.k.a. turned on or activated)

Ch. 10, Sect. 4 – Protein Synthesis

• RNA – single stranded– Uracil instead of

thymine– Ribose instead of

deoxyribose– Shorter than DNA– Folds to form some

double-stranded regions (A-U, C-G)

Types of RNA

• Messenger RNA – carries DNA’s message

• Ribosomal RNA – makes up ribosomes

• Transfer RNA – transfers amino acids to a growing protein

Transcription – in the nucleus

1. Initiation – RNA polymerase binds to promoter on DNA; DNA unwinds

2. Elongation – RNA polymerase moves along the DNA, adding complementary free-floating nucleotides

3. Termination – RNA polymerase reaches STOP signal and falls off

Ch. 11, sect. 1: Turning genes on

• Promoter Region (on DNA) = RNA polymerase binding site (TATA box)

• Transcription Factors (proteins) – help to position RNA polymerase

• Transcription process results in a pre-mRNA strand complementary to gene sequence

Pre-mRNA RNA

• Pre-mRNA contains introns and exons– introns are not translated– exons are translated

• Spliceosomes cut out the introns and bond the exons together– ** exons are the parts that exit the nucleus

as mRNA **

Genetic Code

• Base sequence determines the protein made

• Each 3-nucleotide sequence in mRNA = codon– Codes for one particular amino acid (there are

20) or the STOP signal

• tRNA has a strategically placed anticodon (complementary to codon)– each tRNA holds one particular amino acid

Translation – in cytoplasm

• Initiation – tRNA+methionine and ribosome attach to mRNA

• Elongation – Ribosome moves 3 base pairs down the mRNA and docks the next tRNA+AA [peptide bond]

– polypeptide grows as the ribosome moves along mRNA

• Termination – ribosome reaches STOP– All components separate

From DNA to a Physical Trait

• Scientists mapped DNA

• Knowing location and sequence of gene can help with cure or treatment

Ch. 12 sect. Genetic Disorders

• Carcinogen = cancer-causing agent – chemical (components in tobacco smoke)

– radiation (UV rays, X-rays)

– viral (Human papilloma virus)

• Mutation = change in base sequence of DNA– germ [passed on to offspring], autosomal

[affects organism], lethal [death pre-birth], beneficial [phenotypic change helps organism]

Chromosomal Mutations – During Cell Division

• Deletion

• Inversion

• Translocation

• Nondisjunction

• Point Mutations – occur on a single gene– Substitution (wrong nucleotide) may or may

not change the corresponding amino acid

– Deletion or insertion results in a frameshift

• Codons are grouped incorrectly

Gene Mutations – During DNA Replication or transcription

Prenatal Genetic Testing

• Looks for gene markers • Amniocentesis – analyzes

cells from amniotic fluid

• Chorionic Villi – tests fetal cells

- Good genes put into a virus- Virus injected into fetus- Virus infects fetus, giving it the good gene

Genetic Modification

• GMO or no???