LESSON 14: BACTERIAL GENETICS Flashcards by Rominez, Atasha Ann F.

is the science of heredity; it includes the study of genes and information it carries.

Genetics

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How genes are replicated and transferred to other organisms
or how particular genes are expressed in an organism and how does it influence its
characteristics

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is the genetic information that a cell carry that includes chromosomes and plasmid.

genome

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are containing DNA that carry
hereditary information; the chromosomes carry the genes.

Chromosomes

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are segments of DNA (except in RNA viruses) that code for functional products.

GENES

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A DNA or deoxyribonucleic acid is a macromolecule composed of repeating units called

nucleotides

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nucleotide is consist of of a

Nitrogenous base (adenine, thymine, cytosine or guanine),
Deoxyribose (a pentose sugar), and a Phosphate group

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The cells DNA exist as long strands of nucleotides twisted together in pairs to form a

Double helix

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Each strand has a string of sugar and phosphate group and nitrogenous base attached to each sugar.

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The two strands are held together by

hydrogen bonds

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DNA
The base pairs are
(Thymine and adenine)
(Cytosine and guanine)

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These strands have two designated ends called 5’ and 3’ (you can read that as 5 prime end and 3 prime end).
These numbers indicate end-to-end chemical
orientation.

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is the end, which joins a phosphate group that attaches to another nucleotide.

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end is important as during replication the new nucleotide is added to this end.

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In terms of direction, if one strand is 5’ to 3’ while reading from left
to right, the other strand will be 3’ to 5’. Simply put, the strands run in opposite
directions. This orientation is kept for easy binding between nucleotides of the
opposite strands.

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is the genetic makeup of an organism that codes for all its characteristics.
It is the organisms collection of genes.

Genotype

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actual expressed properties of an organism
or the manifestation of a genotype

phenotype

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A typical bacterial chromosome have a single circular DNA molecule and associated proteins.

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The chromosome is folded and looped and attached to the plasma membrane of a bacteria.

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The flow of genetic information from one generation to the next is made possible through DNA replication, or mRNA transcription.

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If there is adenine in the parent or old
strand, complementary thymine will be added to the new strand.
Similarly, if there is cytosine in the parent strand, complementary guanine will be copied into the new daughter strand.

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To summarize DNA replication

-the two strands uncoil and permanently
separate from each other.
- The base sequence of parent or old strand directs the base sequence of new or daughter strand.

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initiated at the origin of replication.

DNA replication

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Before the DNA synthesis begins, both the parental strands must unwind (due to an enzyme called
and separate permanently into single stranded state made possible by enzyme helicase

topoisomerase or gyrase

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Primers are short sequences of RNA, around 10 nucleotides in length

Primase synthesizes the primers.

The next step involves the addition of new complementary strands. The choice of nucleotides to be added in the new strand is dictated by the sequence of bases on the template strand.

New nucleotides are added one by one to the end of growing strand by an enzyme called D

DNA polymerase

The strand, which is synthesized in the same direction as the replication fork, is known as the

‘leading’ strand.

The DNA polymerase has to attach only once and it can continue its work as the replication fork moves forward.

for the strand being synthesized in the other direction, which is known as the ---- the polymerase has to synthesize one fragment of DNA thus creating many fragments as it moves towards the replication fork.

‘lagging’ strand

These fragments are known as

Okazaki fragments

These gaps are filled by

ligase

Reiji okazaki

When DNA polymerase is adding nucleotides to the lagging strand and creating Okazaki fragments, it at times leaves a gap or two between the fragments

The Replication process is finally complete once all the primers are removed and Ligase has filled in all the remaining gaps.

This process gives us two sets of genes, which will then be passed on to two daughter DNA molecules which are identical to the parent molecule.

The information in a DNA are used to make proteins that controls cell activities.

the synthesis of a complimentary strand of RNA from a DNA template.

transcription

The encoded information is then used by cell to synthesize protein in a process called

translation

wherein genetic information in DNA is copied or transcribed into a complimentary base sequence of RNA.

transcription

carries the coded information for making specific proteins from DNA to ribosomes, where proteins are synthesized.

Messenger RNA (mRNA)

There are three types of RNA in a bacterial cell:

messenger RNA, ribosomal RNA, and transfer RNA

The process of transcription is similar to DNA replication wherein it also uses complementary base pairing as a guide, except that thymine is replaced by a uracil to pair with adenine in an RNA strand

Protein synthesis is called

translation

because it decodes and translates the genetic codes (codons) made during transcription into specific proteins which consists of a series of amino acids.

Sense codons codes into a particular amino acid while nonsense codons signal the ends of protein synthesis thus it is also called

stop codons

The site of translation is the

ribosomes

while transfer RNA (tRNA) recognize the specific codon and transport the corresponding

amino acid

The functions of the ribosomes are to direct the orderly binding of tRNAs to codons and to assemble the amino acids brought there into a chain, ultimately producing protein.

is a regulatory mechanism that inhibits gene expression and decreases synthesis of enzymes, usually in response to overabundance of an end-product (protein).

repression

RNA synthesis starts at a site in the strand called

promoter

until it reaches a site on the DNA called

terminator

is the process that turns on the transcription of genes.

induction

is a change in the base sequence of a DNA which sometimes cause a change in the end-product (protein)

mutation

a single base in one point of a DNA is replaced with another

1. Base mutation (point mutation):

Types of mutation:

1. Base mutation (point mutation): 2. Missense mutation: 3. Frame-shift mutation:

happens when as a result of base mutation, an incorrect amino acid is inserted into the synthesized protein.

Missense mutation

when one or a few nucleotide pairs are inserted or deleted in the DNA

Frame-shift mutation

are environmental agents that directly or indirectly cause mutations

Mutagens

mutagens examples:

1.Chemical mutagens 2. Radiation

Examples of chemical mutagens:

1. nitrous acid 2. nucleoside analog 3. aflatoxins

exposure of bacteria to nitrous acid can convert the base adenine (A) to a form no longer unpairable with thymine at a random location.

also have altered base-pairing property

nucleoside analog

Radiation examples:

1.Xrays and gamma rays 2. . Ultraviolet (UV) light

are potent mutagens due to their ability to ionize atoms

Xrays and gamma rays

a frame-shift mutagen and also a potent carcinogen.

aflatoxin

harmful (at 260 nm wavelength) due to its ability to form covalent bonds between bases.

ultraviolet (UV)

Cell damage due to UV light can be repaired by photolyases or light repair enzymes by destroying covalent bonds to return its original sequence.

is the exchange of genes between two DNA molecules to form new combinations of genes on a chromosome that results to genetic diversity in a population.

Genetic recombination

occurs when genes are passed from an organism to its offspring (plants and animals).

Vertical gene transfer

the transfer involves a donor cell that gives a portion of its DNA to a recipient cell.

Horizontal gene transfer

The recipient cell that incorporates donor DNA to its own DNA is called

recombinant

In bacteria, genetic recombination results from these three types of gene transfer :

1. Transformation 2. Conjugation 3. Transduction

is the transfer of genes from one bacterium to another as “naked” DNA in a solution.

Transformation

in bacteria is a mechanism by which genetic material is transferred by a plasmid.

conjugation

A is a circular piece of DNA that replicates independently from the cells chromosome.

plasmid

is a genetic transfer wherein bacterial DNA is transferred from a donor cell to recipient cell inside a virus that infects bacteria called bacteriophage,

transduction

requires cell to cell contact, only donor cell must carry the plasmid.

conjugation

is an extrachromosomal genetic element that is capable of autonomous replication in the cytoplasm of a bacterial cell.

plasmid

The plasmids can also be present as integrated with bacterial chromosomes, and plasmids integrated with host chromosome are known as

Episomes

Plasmids are present in both Gram-positive and Gram-negative bacteria.

Many plasmids control medically important properties of pathogenic bacteria. These include

(a) resistance to one or several antibiotics, (b) production of toxins, and (c) synthesis of cell surface structures required for adherence or colonization.

transfer antibiotic resistant genes to some organism.

R plasmid

2 categories of plasmid:

1. Transmissibility 2. Nature of plasmid

cell to cell genetic transfer through conjugation

Transmissible

Responsible for synthesis of the sex pilus and for the synthesis of enzymes required for their transfer.

a. transmissible

empty of genes, thus unable to transfer

b. non- transmissible

nature of plasmid

a. F factor b. R (resistance) factor c. Col factor

contains the genetic information, essential for controlling mating process of the bacteria during conjugation.

f factor

These genes determine (a) expression of pili, (b) synthesis and transfer of DNA during mating, (c) interference with the ability of F bacteria to serve as recipients, and (d) other functions.

2 sizes; large plasmid (mol. wt. 60 million); contains R factor and are conjugative, while small plasmids (mol. wt. 10 million)contains “r” factor and non-conjugative

is responsible for conjugational transfer

resistance transfer factor

R factor consists of two components:

The resistance transfer factor (RTF) and resistant determinant (r)

carries resistance for one of the several antibiotics

R determinants

or colicinogenic factor, resembles the F factor in promoting conjugation, leading to self-transfer and also at times transfer of segments of chromosomes

col factor

encodes for production of colicins, which are antibiotics-like substances that are specifically and selectively lethal to other enteric bacteria.

They also encode for production of diphthericin and pyocyanin produced by which are substances similar to colicins.

diphtheriae and Pseudomonas pyocyanea,