Genetics is the study of heredity which is concerned

with how:

information in nucleic acids is expressed nucleic acids are duplicated and transmitted to

progeny these processes account for the characteristics of

progeny

The heredity material found in cells

Large molecules that are acidic in nature

Associated with the nuclear material of cells

Two types

Deoxyribonucleic Acid

Ribonucleic Acid

Is responsible for all cellular activity.

Directs the production of proteins.

Is double stranded and helical.

Is maintained by hydrogen bonds (weak bonds)

Is very stable and can survive Temperatures as high as 70 C High salt concentrations Acid environments

Ribonucleic acid (RNA) is a biologically important type of molecule that consists of a long chain of nucleotide units.

Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate. RNA is very similar to DNA, but differs in a few important structural details: in the cell, RNA is usually single-stranded.

Three types of RNA

mRNA messenger

tRNA transfer

rRNA ribosomal

mRNA messenger

Is complementary to one strand

of DNA and functions to carry the genetic material from the chromosome to the ribosome.

Transcription

tRNA transfer

Is responsible to transfer information from mRNA to rRNA.

Translation

rRNA ribosomal

Is associated with the ribosome

and accepts information from tRNA and correlates the information to synthesize proteins.

Protein Synthesis

Are constructed from a string of small molecules calledNucleotides.

Nucleotides consist of a 5-carbon sugar (pentose), one or more phosphate groups, and a base containing nitrogenous rings.

Purines

Contain 2 nitrogenous rings

Adenine and Guanine

Pyrimidines

Contain 1 nitrogenous ring

Cytosine and Thymine in DNA

Uracil replaces Thymine in RNA

Adenine always pairs with Thymine in DNA (A-T)

Uracil replaces Thymine in RNA

Guanine always pairs with Cytosine (G-C) and are

stronger bonds.

The central dogma theory of molecular biology is

represented by a simple pathway: DNA—>RNA-->protein, which demonstrates the flow of

genetic information in a living cell.

The major processes involved in this pathway are replication, transcription, and translation.

In DNA replication, the DNA polymerase enzyme replicates all the DNA in the nuclear genome in a semi-conservative manner, meaning that the double stranded DNA is separated into two and a template is made by DNA polymerase.

This allows genomic material to be duplicated so it can be evenly partitioned between two somatic cells (daughter cells) upon division.

The process in which DNA is copied into RNA by RNA Polymerase is called transcription.

Three forms of RNA are produced

here: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).

1. DNA guides the synthesis of mRNA which in turn directs the order in which amino acids are assembled into proteins.

2. DNA directs its own replication by giving rise to two complete, identical DNA molecules.

This replication is necessary because each cell must inherit a complete set of all genes in order to carry out the cell’s life processes.

Another process in this pathway is reverse transcription, which involves copying RNA information into DNA using reverse

transcriptase.

Recently, this processes has been defined and may expand the central dogma.

For example, retroviruses use the enzyme "reverse transcriptase" to transcribe DNA from a RNA template.

The viral DNA then integrates into thenucleus of the host cell. Then it is transcribed, and further translated

into proteins.

This biological process effectively adds another pathway to the central dogma of molecular biology.

Bacteria contain 1 chromosome

Many contain plasmids

When bacterial chromosomes replicate both strands are duplicated. Each strand functions as a template.

During replication, enzymes known as polymerases transport nucleotides from the cytoplasm that are complimentary to the template and fit them into place, resulting in two strands, one parental and one new one

During replication, enzymes known as polymerases transport nucleotides from the cytoplasm

that are complimentary to the template and fit them into place, resulting in two strands, one parental and one new one.

The replication is said to be semi-conservative because the parental strand is conserved (remains the same ).

DNA unwound with enzyme (replication fork)

Complementary bases added to template (parent strand) using enzyme

Replication fork moves down strand

Newly replicated DNA rewinds

Process called Semiconservative Replication

Copied in 5’ to 3’ directionPolymerase can only add nucleotides to 3’ end

In Prokaryotes, replication begins at specific site in chromosome called the origin of replication

Replication of DNA begins a specific site on the DNA template termed the origin and proceeds in both directions from the origin until nuclear division and cytokinesis take place.

Replication speed = 1000 nucleotides/sec

Transcription is the synthesis of RNA and involves the assembly of nucleotides by an enzyme, RNA polymerase.

1. RNA polymerase binds to DNA at a promoter site near the gene to be transcribed.

2. RNA polymerase travels the length

of the DNA using it as a template toduplicate.

3. The RNA polymerase continues until it reaches a termination site atwhich time the transcription is complete.

Protein synthesis is carried out in the cytoplasm.

It begins with DNA duplication by mRNA (Transcription)

mRNA then migrates to the ribosome where tRNA transfers information from mRNA to rRNA (Translation).

Protein synthesis is continuous and takes place

in three stages:

1. Initiation

2. Elongation

3. Termination

Initiation

The beginning of protein synthesis starts methionine which is the start codon.

Start codon is know as formylmethoinine (f-met).

It is coded as AUG.

Elongation

By a complex that begins with

f-met, amino acids attach to form a chain (amino acids joined repeatedly to form proteins)

Termination

Ends when the synthesis comes to a termination codon.

Termination codons are codes

as UAA, UAG, and UGA).

A codon is a group of three nucleotides in DNA which

acts as a code in the placing of an amino acid in a protein molecule.

A codon is a group of three nucleotides in DNA which

acts as a code in the placing of an amino acid in a protein molecule.

A codon is a group of three nucleotides in DNA which

acts as a code in the placing of an amino acid in a protein molecule.

AUG begins protein synthesis

UAA, UAG, UGA are termination codons.

One base pair is exchanged for another in the DNA molecule

One or more base pairs are inserted in the DNA molecule.

One or more base pairs are deleted in the DNA molecule

There is a rearrangement of sections in the DNA molecule.

There is an exchange of DNA region with another DNA molecule

(Recombination).

Some mutations harmful, some beneficial, some neutral

Some plasmids encode for genes that enhance pathogenicity of a bacterium

E-coli, plasmid encodes toxins produced and bacterial attachment to intestinal cells

Transposons: are small pieces of DNA (2,000 – 20,000 base pairs) fond in chromosomes and plasmids.

They are able to direct synthesis of copies of themselves and become incorporated into the chromosome.

Called “jumping genes” because of their ability to insert themselves into a chromosome or change their locations.

Chemical and physical agents that cause mutations.

UV light is absorbed by pyrimidines (cytosine and thymine). UV

causes adjacent thymines in the same strand to react and bond

with each other.

Thymine dimers are replication errors in transcription; if not correct , can lead to cellular death.

◦ Agents in environment that directly or indirectly cause mutation

Nitrous acid alters the chemical structures of adenine, cytosine, and guanine so that they change the base pairing which introduces mutation during DNA replication.

There are many agents in environment that directly or indirectly cause mutation

Most mutations are harmful but some are beneficial because

they introduce variability into the progeny which promotes survival.

Recombination: exchange of homologous genes on a chromosome

Transformation: genes transferred from one bacterium to Another. After cell death, some bacteria are lysed and

release cellular contents into surrounding environment. The recipient cell is in a physiological state that will allow it to take up

DNA.

Transformation occurs naturally among a few organisms..

Another form of transfer of DNA from

one cell to another.

Requires cell to cell contact andtransfer of plasmids through f-factor pili.

◦ Donor cells carry plasmid◦ Recipient cells usually do not

have plasmid

Streptococcus pneumoniae: S form encapsulated, R form non-encapsulated

◦ Experiment which placed heat killed S form with live R form.

◦ Resulted in live S form.

Transfer of genes from a donor to a recipient by

a bacteriophage