MICRO101A - Microbial Genetics 2

Supplementary Lecture

Nucleic Acids

Nucleic Acids

heredity material found in cells

Nucleic Acids

Large molecules that are acidic in nature

Nucleic Acids

Associated with the nuclear material of cells

2 Types of Nucleic Acids

• Deoxyribonucleic Acid

• Ribonucleic Acid

Deoxyribonucleic Acid

responsible for all cellular activity.

Deoxyribonucleic Acid

Very stable and can survive:

• temperatures as high as 70 C

• high salt concentrations

• Acid environments 

Deoxyribonucleic Acid

Directs the production of proteins

Deoxyribonucleic Acid

double stranded and helical

Deoxyribonucleic Acid

maintained by hydrogen bonds (weak bonds)

Ribonucleic Acid

molecule that consists of a long chain of nucleotide units

Ribonucleic Acid

 Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate

Ribonucleic Acid

single-stranded

3 Types of Ribonucleic Acid

• mRNA (messenger)

• tRNA (transfer)

• rRNA (ribosomal)

mRNA (messenger)

complementary to one strand of DNA

mRNA (messenger)

Functions  to carry the genetic material from the chromosome  to the ribosome

mRNA (messenger)

Synthesized during Transcription

tRNA (Transfer)

responsible to transfer information from mRNA to rRNA

tRNA (Transfer)

Involved in the Translation Process

rRNA (ribosomal)

associated with the ribosome

rRNA (ribosomal)

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

rRNA (ribosomal)

Involved in Protein synthesis

Nucleotides

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

2 Base Types

• Purines

• Pyrimidines

Purine

• Contain 2 nitrogenous rings

• Adenine and Guanine

Pyrimidines

• Contain 1 nitrogenous ring

• Cytosine and Thymine in DNA

• Uracil replaces Thymine in RNA

Rules for base Pairings

• 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

Central Dogma Theory

DNA >RNA-->protein

• flow of genetic information in a living cell

Central Dogma Theory

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

DNA polymerase enzyme; DNA polymerase

In DNA replication, the ____ __________ _________ 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 Replication

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

transcription

The process in which DNA is copied into RNA by RNA polymerase is called ___________.

Transcription

This process produces the 3 forms of RNA (mRNA, rRNA, & tRNA)

mRNA

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

two

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

DNA replication

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

Reverse Transcription

involves copying RNA information into DNA using reverse transcriptase

retroviruses; viral DNA

__________ use the enzyme "reverse transcriptase" to transcribe DNA from a RNA template. The_____ ___ then integrates into the nucleus of the host cell. Then it is transcribed, and further translated into proteins.

Bacteria

contain 1 chromosome and many contain plasmids

DNA Replication in Bacteria

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

DNA Replication in Bacteria; parental

During ________________, 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 ___________ and one new one

DNA Replication in Bacteria

What type of process is shown in the photo?

semi-conservative

DNA Replication in Bacteria is said to be _________ because the parental strand is conserved (remains the same ).

Steps of DNA Replication

1. DNA unwind with enzyme (replication fork)

2. Complementary bases added to template (parent strand) using enzyme

3. Replication fork moves down the strand

4. Newly replicated DNA rewinds

5. Process called semiconservative replication

DNA Replication

Copied in 5’ to 3’ direction

RNA Synthesis in Bacteria

1. involves the assembly of nucleotides by an enzyme, RNA polymerase.

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

3. RNA polymerase travels the length of the DNA using it as a template to duplicate.

4. The RNA polymerase continues until it reaches a termination site at which time the transcription is complete.

Protein Synthesis in Bacteria

1. carried out in the cytoplasm.

2. Begins with DNA duplication by mRNA (Transcription)

3. mRNA then migrates to the ribosome where tRNA transfers information from mRNA to rRNA

4. (Translation).

3 Stages of Protein Synthesis

1. Initiation

2. Elongation

3. Termination

Initiation Stage (Protein Synthesis in Bacteria)

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

Initiation Stage (Protein Synthesis in Bacteria)

• Start codon is know as formyl methionine  (f-met).

• It is coded as AUG.

Elongation Stage (Protein Synthesis in Bacteria)

By a complex that begins with f-met, amino acids attach to form a chain (amino acids joined repeatedly to form proteins)

Termination Stage (Protein Synthesis in Bacteria)

• Ends when the synthesis comes to a termination codon.

• Termination codons are codes as UAA, UAG, and UGA.

Codon

group of three nucleotides in DNA which acts as a code in the placing of an amino acid in a protein molecule

AUG

codon that begins the protein synthesis

UAA, UAG, UGA

termination codon/s

Changes in the DNA molecules can cause Mutations

• 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

Changes in the DNA molecules can cause Mutations

• 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

Plasmids

some ____ encode for genes that enhance pathogenicity of a bacterium

E. coli

Some _____ carries plasmids that encodes toxin production and bacterial attachment to intestinal cells

Transposons

are small pieces of DNA (2,000 – 20,000 basepairs) found in chromosomes and plasmids.

Transposons

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

Transposons; jumping genes

________ are called “___________” because of their ability to insert themselves into a chromosome or change their locations.

Mutagens

• 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

Mutagens

• 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.

lysed; recipient

After cell death, some bacteria are _____ and release cellular contents into surrounding environment. The ______ cell  is in a physiological state that will allow it to take up DNA.

Transformation

_________ occurs naturally among a few organisms..

Conjugation

Another form of transfer of DNA from one cell to another.

Conjugation

• Requires cell to cell contact and transfer 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.

Transduction

Transfer of genes from a donor to a recipient by a bacteriophage

Polymerase

__________ can only add nucleotides to 3’ end

Origin of replication

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

Replication of DNA; both

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

Replication speed

1000 nucleotides/sec