AP Bio Unit 6

What is the structure of DNA?

Molecules called nucleotides, each nucleotide has a phosphate group, sugar group, and a nitrogen base. Its made up of 2 strands forming a double helix

Role of Alfred Hershey and Martha Chase in discovering the structure of DNA

-Alfred Hershey and Martha chase performed experiments showing that DNA is the genetic material of a phage known as T2
-They designed an experiment showing only 2 components of T2 (DNA or protein) enters an E.coli cell during infection.
-They concluded that the injected DNA of the phage provides genetic information

Steps of DNA replication

-Initiation
-Elongation
-Termination

Initiation

Proteins bind to origin of replication while helicase unwinds the DNA helix and two replication forks formed at the origin of replication.

Elongation

Primer sequence is added with complementary RNA nucleotides which are replaced by DNA nucleotides

Termination

Occurs when converging replication forks meet on opposite ends of parental chromosome.

Replication

making of DNA from an existing DNA strand

Transcription

Synthesis of RNA under the direction of DNA (making a copy of a gene)

Translation

Synthesis of a polypeptide using info in the mRNA (making the gene a protein)

Gene Expression

The process by which DNA directs protein synthesis includes two stages; transcription and translation

How do mutations change the amino acid sequence of a protein?

The change of a single nucleotide in a single a DNA template strand can lead to the production of an abnormal protein.

How do eukaryotic cells modify RNA after transcription?

-enzymes in the eukaryotic nucleus modify pre mRNA (RNA processing) before the genetic messages are dispatching to the cytoplasm.
-During RNA processing, both ends of the primary transcript are altered

5 end and 3 end

-5 end gets a modified nucleotide 5cap

• 3 end gets a Poly-A-tail

What function do the modified ends share

-facilitate the export of mRNA
-protect mRNA from hydrolytic enzymes
-help ribosomes attach to the 5 end

Splicing

Removes introns and joins exons, creating an mRNA molecule with a continuous coding sequence

What are the 3 parts of an operon

-operator
-promoter
-genes of the operon

Operon

Entire stretch of DNA that includes the operator, promoter and the genes they control

Operator

The regulatory switch is a segment of DNA usually positioned within the promoter.

Promoter

The DNA sequence where RNA polymerase attaches

Repressible operon

Usually on and it's binding of a depressor to the operator and shuts off transcription (TRP operon)

Inducible operon

Usually off and a molecule called an induced inactivates the repressor and turns on transcription (lac operon)

Repressor genes

Prevents gene transcription by binding to the operator and blocking RNA polymerase

Impact of DNA methylation

Causes DNA to be more tightly packed and therefore reduces gene expression

Impact of histone acetylation

Makes chromotin less tightly packed and encourages transcription on gene expression

Role of gene regulation in embryonic development and cancers

It regulates the development and Uncontrolled gene expression results in cancers.

Components of a virus

Small infectious particle that has a nucleic acid, and enclosed in a protein coat and a membranous envelope

Lytic cycle

Ends in death of the host cell by rupturing it

Lysogenic cycle

The bacteriophages DNA becomes incorporating into the host cells DNA and its replicated along the host cells genome

Gel electrophoresis

Rapidly analyzes and compares genomes. Lab technique used to separate macromolecules primarily DNA and proteins.

Bacterial transformation

Transformation is the process by which foreign DNA is introduced into a cell. Transformation of bacteria with plasmids is important not only for studies in bacteria but also because bacteria are used as the means for both storing and replicating plasmids. Because of this, nearly all plasmids (even those designed for mammalian cell expression) carry both a bacterial origin of replication and an antibiotic resistance gene for use as a selectable marker in bacteria.

PCR

Polymerase chain reaction - used in biotechnology. Produces many copies of a specific target segment of DNA

Practical applications of DNA technology

Medical, diagnosis of disease, gene therapy, pharmaceutical products, forensics, agriculture and environmental clean up

Wilkins and Franklin

Used a technique called X-ray crystallography to study molecular structure

James Watson and Crick

Introduced an elegant double helical model for the structure of deoxyribonucleic acid or DNA

Avery, McCarty and Macleod

Announced that the transforming substances was DNA

Erwin Chagraff

Reported that DNA composition varies from one species to the next
-base composition of DNA varies between species
-in any species, the numbers of A and T bases are equal and the number of G and C bases are equal