Genetics is the study of heredity which is concerned with how: information in nucleic acids is...
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Transcript of Genetics is the study of heredity which is concerned with how: information in nucleic acids is...
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