Microbiology- Chapter 9 ( Microbial Genetics)

Front 1

where is genetic information found in prokaryotes?

Back 1

chromosomes, plasmids

Front 2

Where is genetic information found in eukaryotes?

Back 2

chromosome, mitochondria, chloroplasts, plasmids

Front 3

WHere is genetic info found in viruses?

Back 3

DNA & RNA

Front 4

What are the levels of genetic research?

Back 4

organismal, cell, chromosome, molecular

Front 5

How many genes does E.Coli, and human cell have?

Back 5

E. coli 4,288 genes
Human cell: 30,000 - 40,000
size of the cell of E. coli (1 um - diameter)
Size of stretched out DNA - 1mm (1000 times longer than size of cell)

Front 6

How is DNA packaged?

Back 6

DNA molecule is tightly packed in the form of chromosome

Front 7

Describe the structure of DNA.

Back 7

DNA Molecule - double helix
composed of nucleotides:
nucleotides are composed of
bases:
purine (adenine, guanine)
pyrimidine (cytosine, thymine)
strand:
deoxyribose sugar
phosphate group

Single strands of DNA have opposite orientation (3’ and 5’)

Front 8

What is the overall process of DNA replication?

Back 8

double helix unwinds - unzipping hydrogen bonds
bases of single stranded DNA exposed
Replication fork is formed
synthesis of the new strand by attachment of complementary nucleotides
Enzymes involved in DNA Replication
helicase - untwists the DNA helix by braking the H bonds
Primase - synthesis of RNA primer
DNA polymerase III - adding bases to the new DNA
Ligase - joining of the DNA fragments
Gyrase - supercoiling

Front 9

Describe DNA replication in detail.

Back 9

Short RNA primer attached to the origin of replication
complementary nucleotides attach themselves to the exposed bases (A-T, C-G)
DNA polymerase III joins the added nucleotide into a growing DNA strand
Semiconservative replication (double stranded DNA contains one old and one new strand)
Additional Info
leading strand is synthesized continuously
lagging strand is synthesized in pieces (Okazaki fragments)
synthesis starts with a short RNA primer
The strands are synthesized in the 5’ to 3’ direction
DNA polymerase I removes RNA primers
Lygase joins the fragments
Bidirectional -

Front 10

What is the flow of genetic information?

Back 10

1. DNA replication - reproduction of cells
2. transcription - information contained within DNA is copied -> RNA
3. translation - polypeptides synthesized from RNA nucleotide sequences -> amino acid sequence of protein

Front 11

What are the forms of RNA?

Back 11

messenger (RNA (mRNA)
ribosomal RNA (rRNA)
transfer RNA (tRNA)
small RNA’s (regulatory function)
Primer RNA
Ribozymes - RNA enzymes

Front 12

Describe transcription.

Back 12

Synthesis of RNA from DNA as a template :
messenger RNA (mRNA) is formed by transcription of a portion of DNA (gene)
Sequence of nucleotides from DNA are rewritten in RNA

Process:
RNA polymerase binds to DNA segment (known as “promoter”)
Unwinds the double helix of DNA
One DNA strand acts as a template for synthesis of RNA
RNA polymerase puts free nucleotides forming RNA chain
As the polymerase moves along the DNA new strand RNA grows
When the RNa polymerase reaches the sites of DNA called terminator - the transcription ends - RNA polymerase and new RNA strand are released

Front 13

Describe translation.

Back 13

The process of translating nucleic acids language into the language of proteins (sequence of AA)
Codons are groups of three nucleotides (mRNA)
The sequence in the codon determines which AA will be incorporated into a protein
Takes place in the Ribosomes

Front 14

Describe protein synthesis.

Back 14

ribosomes moves along mRNA and reads the codons
Transfer RNA (tRNA) has a sequence of three bases - anticodons complementary to codons
For each AA there is a specific tRNA
The first tRNA recognizes the start codon and brings methionine

Front 15

Describe elongation and termination.

Back 15

peptide bonds are formed between amino acids - polypeptide is formed
blank tRNA discharged
when nonsense codon is reached, translation is terminated
ribosome is separated into its subunits

Front 16

what is Simultaneous Transcription and Translation

Back 16

ast process
more than one ribosome reads one mRNA molecule
Most genes (75%)are constitutive - their products are produced constantly
other genes are regulated so they are only transcribed and translated when needed

Front 17

How is Transcription and Translation in Eukaryotes?

Back 17

the introns - non protein coding segments of DNA are transcribed but not translated
the genes need to be processed
the introns are cut out

Front 18

What is repression?

Back 18

Mechanisms of Genetic Control
repression
inhibition of gene expression
meditated by a protein - repressor

Front 19

What is induction?

Back 19

Mechanisms of Genetic Control:
Induction
The triggering of a specific gene by an inducer molecule (which acts directly or indirectly by affecting an RNA polymerase molecule)

Front 20

what is the Operon Model of Gene Expression?

Back 20

Inducible operon - lactose operon - must be activated by inducers
Functional genes consists of
regulatory genes
operon
control region
promoter - RNA polymerase initiates transcription
operator - go or stop signal
Structural genes
b-galactosidase
lac permease
transacetylase

Hint 20

http://www.mun.ca/biochem/courses/4103/topics/operon.html

Front 21

What is a mutation?

Back 21

change in the genetic material
during the replication of DNA - an error in base sequence may occur - mutation
it can be:
spontaneous
induced
Mutation can have beneficial or deleterious (lethal) effects)
beneficial - mutant enzyme - enhanced activity (rare)
lethal - lost activity of the enzyme (almost always)

Front 22

what are the causes of mutations?

Back 22

Causes
spontaneous
induced (mutagens - chemicals, radiation)
significance of mutation in microbes

Front 23

what are the Categories of Mutations?

Back 23

point mutation - substitution, insertions, and deletions of a single base in the DNA
Missense mutation - substitution of one AA (inactive or reduced activity protein)
Nonsense mutation - creating a stop codon in the middle protein
frameshift mutation - deletion or insertion of a single nucleotide or DNA fragment; causes changes in many AA’s

Front 24

what are mutagens?

Back 24

chemicals - nitrous acid (converts adenine into form that pairs with C instead T)
Nucleoside analogs (molecules that are structurally similar to normal bases)
Radiation
x-rays, gamma rays (errors in replication; physical damage of DNA)

Front 25

what is the AMES test?

Back 25

AMES Test - Identifying Carcinogens by Using Bacteria
The method uses bacterium Salmonella which is a histidine auxotroph mutant (can not grow without His)
In the presence of a mutagen, it can undergo back - mutation
Salmonella is grown in the presence and absence of suspected mutagen
90% of substances found to mutagenic by AMES test are also carcinogenic
this method is widely used

Front 26

what is transformation?

Genetics

Back 26

fragments of the DNA are transferred from one microorganism to another one - incorporated into genome
experimentally shown (but not understood) by Frederick Griffith in England in 1928

Front 27

what is conjugation?

Genetics

Back 27

“sexual contact” between two mating cells
donor cell has sex pilli and F+ (fertility factor)
a gene located on the plasmid
DNA is transferred from one cell to another through sex pillus

Front 28

Describe transduction.

Back 28

the transfer of genetic material from one bacterium to another by means of a bacteriophage vector

Front 29

Describe transponsons.

Back 29

A DNA segment with an insertion sequence at each end, enabling it to migrate to another plasmid, to the bacterial chromosome or to a bacteriophage.

Front 30

what is a phenotype?

Back 30

phenotype - manifestation of genotype (ability to perform particular chemical reaction)

Front 31

what is a genotype?

Back 31

genotype - the sum of all genes (Genetic make-up)

Front 32

what is a gene?

Back 32

a segments of DNA that codes for a functional product (protein)

Front 33

what is a chromosome?

Back 33

cellular structure in which the DNA molecule is packaged