ch 16: molecular basis of inheritance ch 17: from gene to protein ch 18: control of gene expression...

• Ch 16: Molecular Basis of Inheritance• Ch 17: From Gene to Protein• Ch 18: Control of Gene Expression• Ch 18: Gene Mutation

• 1928• Involved 2 strains of bacteria that caused pneumonia• Key concept: Transformation

• (1944)• They were able to identify DNA as Griffiths transforming principle. • Took extract (from heated smooth bacteria) and treated

it with DNAase (digests DNA) - then mixed with rough bacteria and injected into rats -> the rats lived.• In other side of experiment, treated extract with

protease (digests proteins) -then mixed with rough bacteria and injected into rats -> rat died.

• This showed that DNA, not protein, has ability to transform cells.

Scientists were able to discover that DNA was responsible for containing the genetic information responsible for an organisms biochemical make up.

1950Rules of base pairingNumber of A’s = number of T’sNumber of C’s = number of G’s

If in a DNA molecule there were 23% A,What is the % of G?

• Worked with Maurice Wilkins.• Process called x-ray diffractionis what ultimately proved the Double helix of DNA.• Died in 1958 of ovarian cancer,most likely caused by the radiationshe worked with.

• Built the first model of DNA.• Work based on previous data,including Franklin’s.• Also provided the explanation forhow DNA replicates.

• Components:– Sides– Rungs– Purines and pyrimidines

• Nucleotides

• Semi-conservative Replication

Antiparallel: one strand (5’ 3’), other strand runs in opposite, upside-down direction (3’ 5’)

• Enzymes:– DNA Helicase- “unzips” DNA/unwinds strand.

Replication fork formed here.– Leading strand.– RNA Primase- RNA primer to get replication going.– DNA Polymerase- “attaches” DNA nucleotides to

template.– Lagging Strand– Okazaki Fragments- chunks of lagging strand– DNA Ligase- links Okazaki fragments together

• One Gene / One Enzyme Hypothesis:– Genes control the production of enzymes.– Disorders such as PKU and albinism examples.– One gene / one protein (as not all enzymes are

proteins) -> one gene / one polypeptide.• DNA found in nucleus, protein synthesis occurs

in cytoplasm.• RNA must be transcribed from DNA and travel

from the nucleus to cytoplasm.

• Sugar is Ribose• Uracil replaces Thymine• Single stranded• Three Types:

– mRNA- carries message for what protein should be made from the nucleus to cytoplasm.

– tRNA- transfers amino acids to ribosomes to build the polypeptide.

– rRNA- along with proteins, makes up ribosomes.

• Occurs in the nucleus; mRNA is made.• Labeled mRNA has been

photographed leaving nucleus.• mRNA carries the code for what

proteins are needed.• Codons

– Sequence of 3 bases coding for aa’s.– 64 possible combinations of bases; some

aa’s have multiple codons.– 61 code for aa’s; 3 are stop codons.

• Promotor site, coding region, termination site.• RNA Polymerase is multi-functional.• Introns and Exons:

– Introns are intra-gene segments that are NOT expressed in the final protein. Removed by rybozymes. Occurs in nucleus.

– Exons ARE expressed in final protein. Leave nucleus as a mature mRNA molecule.

1. Initiation

Transcription factors must recognize TATA box before RNA polymerase can bind to DNA promoter

Eukaryotes:TATA box = DNA sequence (TATAAAA) upstream from promoter

2. Elongation

• RNA polymerase adds RNA nucleotides to the 3’ end of the growing chain (A-U, G-C)

2. Elongation

As RNA polymerase moves, it untwists DNA, then rewinds it after mRNA is made

3. Termination

RNA polymerase transcribes a terminator sequence in DNA, then mRNA and polymerase detach.

It is now called pre-mRNA for eukaryotes.

Prokaryotes = mRNA ready for use

• Occurs in cytoplasm when mRNA joins with a ribosome and tRNA molecules.

• mRNA is translated/converted into a polypeptide sequence.

• Remember, this is a proteins primary structure!

• Initiation– Ribosomal subunits join together at the start

codon AUG; tRNA connects to mRNA to begin process.

• Elongation– Polypeptide lengthens; a ribosome can

accommodate 3 tRNA’s.• Termination

– Occurs when ribosome reaches stop codon; no amino acid is coded for. Ribosome dissociates.

• Eukaryotic Cells mechanisms grouped by where they occur.

• Transcriptional Control– Nucleus- rate at which transcription occurs.– Due to organization of chromatin and

transcription factors that get things going.• Post-Transcriptional Control

– Nucleus- rate of processing of introns/exons and rate that it leaves the nucleus.

• Translational Control– Cytoplasm– Life expectancy of mRNA, ability to bind to

ribosomes• Post-Translational Control

– Cytoplasm– Further modification of the polypeptide

produced.

• Operon– A series of genes that code for specific

products and the regulatory elements that control those genes.

• Composed of several parts.

• Promoter– Sequence of DNA where RNA polymerase

attaches.• Operator

– Sequence of DNA where a repressor protein can attach.

– It is coded for by a regulator gene– When a repressor protein is attached

here, transcription does not occur.

• Structural Gene– One or several genes that code for

enzymes.– When transcribed, metabolic pathways

are active• Regulator Gene

– Located outside the operon. Codes for a repressor protein that binds to an operator, in turn regulating the activity of a structural gene.

What happens when

DNA is altered?

Click me

An alteration in the normal sequence of DNA.

A substance that causes an alteration in the normal sequenceof DNA.

The organism that contains an alteration in the normal sequenceof DNA.

Definitions:

Type of mutation where onlyone base in the DNA sequence is changed.

Ex: The dog ate the cat

The dog ate the carKEY: mild to severe mutation. Could result in a differentAmino acid being put into the protein (sickle cell anemia)

Types of Mutations:

Type of mutation where abase is added or deletedin the DNA sequence and every codon from thatpoint on is changed.

Ex: The dog ate the cat

Thd oga tet hec atKEY: the protein will be non-functional, probably resultingin death of the organism.

Types of Mutations:

Types of Chromosome Mutations:

1. Attachment - Virus attaches to cell 2. Entry - viral DNA/RNA enters cell3. Provirus – Viral DNA/RNA becomes part of the host cell

chromosome

4. Replication – Viral gene is replicated with every cell replication.

IN RETROVIRUSES (viruses like HIV w reverse transcriptase) - RNA is reverse-transcribed into DNA, which is integrated into the host cell's genome (when it becomes a provirus), & then undergoes the usual transcription/translation processes to express the viral genes carried by host

Restriction enzymes are endonucleases

• Bacterial enzymes • Different bacterial strains express different restriction enzymes • The names of restriction enzymes are derived from the name of the bacterial strain they are isolated from • Cut DNA into defined and REPRODUCIBLE fragments • Basic tools of gene cloning

EcoRI -  from Escherichia coli BamHI - from Bacillus amyloliquefaciens HindIII - from Haemophilus influenzae PstI -  from Providencia stuartii Sau3AI - from Staphylococcus aureus AvaI -  from Anabaena variabilis

Restriction enzymes recognize a specific short nucleotide sequence

restriction enzymes

Hind III CUTS AT SEQUENCE AAGCTT

Gene Therapy – Deliver genes to a cell that is defective. Works best on disorders that result from the loss of a single protein.

Process – Isolate the functional gene Insert the healthy gene into a viral vector

Introduce the recombinant virus to the patient Virus inserts healthy gene to defective cell

DANG!