Ch. 8 Microbial Genetics and Genes
Genome of all non viral cells are
DNA
Repressible (operon)
(repression) genes in a series are turned OFF by the product synthesized: -anabolic operon
RNA consist of
-5 carbon sugar is ribose -One of 4 nitrogenous bases - adenine, uracil (instead of thymine), guanine, or cytosine -Phosphate
some other traits acquired by conjugating bacteria
-Drug or antibiotic resistance (acquired first by random mutation in the DNA that gives bacteria a selective advantage in its environment) -New enzymes -Toxin production -Metal resistance
Translation
-Each "triplet" of nucleotides on the mRNA, called a codon, specifies a particular amino acid. The information contained in the mRNA molecule is used to produce proteins in a process called translation, which occurs in the ribosome (which is in the cytoplasm).
examples of conjugation
-Gram-negative cells have a fertility factor, which is a plasmid that contains genes that code for the synthesis of a conjugative pilus -Recipient cell is a related species or genus without a fertility factor -Donor replicates its plasmid and then transfers fertility factor to recipient through its pilus; now recipient can synthesize pili, thus acquiring a new ability to initiate "sex" (to conjugate)
Transcription
-Information stored on the DNA molecule is conveyed to "messenger RNA" molecules (mRNA) through the process of transcription (occurs at the chromosome)
DNA Replication
-Making an exact duplicate of the DNA involves 30 different enzymes -Begins at an origin of replication
the master genetic code
-Represented by the mRNA codons and the amino acids they specify -Code is universal -Code is redundant (repetitious)
Application of the DNA code
-The enzyme RNA polymerase binds the DNA at the starting point of the gene to be transcribed, and begins binding together nucleotides that are complementary but in the same sequence as those within the DNA template strand, forming the mRNA segment. -The mRNA segment then moves to a ribosome where the code is translated into a protein. (Note: "AUG" is always the first triplet of nucleotides in the mRNA, and always codes for the first amino acid in a protein, so the first triplet in the template strand is "TAC".)
a gene is
-The fundamental unit of heredity responsible for a given trait -Site on the chromosome that provides information for a certain cell function -Segment of DNA (a specific sequence of nucleotides) that contains the necessary code to make a protein or RNA molecule
a mutation can result IN:
-a variance in morphology -nutritional characteristics -genetic control mechanisms -resistance to chemicals -antibiotics, etc.
DNA polymerase
-adds nucleotides -Both strands are copied (synthesized) -removes the RNA primers and replaces them with DNA -Separation of the daughter molecules is complete
transduction
-bacteriophage serves as a carrier of new genes by acquiring random fragments of the host cell's DNA during assembly of new viruses within the host cell
Transformation
-chromosome fragments from a lysed cell are accepted by a recipient cell that has special DNA-binding proteins on its cell wall; the genetic code of the DNA fragment is acquired by the recipient and inserted into its own chromosome -Donor and recipient cells can be unrelated species
lactose operon is made of what?
3 genes each coding for an enzyme needed to catabolize lactose : -b-galactosidase -permease -b-galactosidase transacetylase
smallest virus has how many genes?
4-5
human cell (gene size)
46 chromosomes containing 31,000 genes; 6 feet long
Each nucleotide consists of 3 parts
A 5 carbon sugar - (deoxyribose) A phosphate group One of 4 nitrogenous bases
Mutations definition
A change in phenotype due to a change in genotype (i.e., a change in the nitrogenous base sequence of DNA)
mutant strain
An organism that has a mutation
nucleotide
Basic unit of DNA structure is a
Genome of viruses are
DNA or RNA
what turns on the Lac Operon?
Lactose: -Binding of lactose to proteins covering and blocking the DNA code turns the genes "on" and genes are transcribed.
DNA definition?
Nitrogenous bases covalently bond to a carbon of each sugar and span the center of the molecule to pair with an appropriate complementary base on the other strand
the "backbone"
Nucleotides covalently bond (share electrons) in an arrangement that forms a sugar-phosphate linkage
what constitutes the DNA code?
Order of bases
repair of mutations
Since mutations can be potentially fatal, the cell has several enzymatic repair mechanisms in place to find and repair damaged DNA (uses DNA polymerase)
what is RNA
Single-stranded molecule made of nucleotides
wild type (wild strain)
The natural, non-mutated characteristic of a mutation
what does a mutation result FROM?
a deleted, added, or substituted nucleotide, which changes the sequence and thus the code
operons
a set of genes, all of which are regulated as a single unit
catabolic operon
a set of structural genes that code for the synthesis of an enzyme needed to metabolize (break down, catabolize) a nutrient; this inducible operon is "induced" when the substrate (nutrient) is present;
anabolic operon
a set of structural genes that code for the synthesis of an enzyme used to synthesize (anabolism) products, such as an amino acid; this repressible operon is "repressed" by the product of which the enzyme catalyzes the production of. (as the product accumulates, it turns off the very gene that produces it, so that too much is not produced.)
bacterial chromosomes are
a single circular loop
what does each DNA strand provide?
a template for the exact copying of a new strand
what is an anticodon?
a triplet of nucleotides that binds to a complementary codon in the mRNA. Hence the amino acids are brought to the ribosomes in the proper order, and then bonded together in the proper sequence.
bacteriophage
a virus that infects bacteria
what does viral genome require?
access to host cell's genetics and metabolic machinery to instruct the host cell to synthesize new viral particles
4 nitrogenous bases (DNA)
adenine, guanine, thymine, or cytosine
4 nitrogenous bases (RNA)
adenine, uracil (instead of thymine), guanine, or cytosine
Methionine
all amino acids start with AUG (a start codon)
There exist a specific tRNA molecule for each kind of
amino acid
each tRNA carries?
an anticodon
bacteriophages produce
an enzyme that breaks up the host cell DNA
mutagens
are physical (primarily radiation) or chemical agents that interact with DNA in a disruptive manner
mRNA characteristics
are relatively short single-stranded segments of nucleotides that code for proteins
example of phenotype
blue eyes
what do tRNA (transfer RNA) do?
bring the proper amino acids to the ribosomes, in the sequence encoded in the mRNA. (during translation)
what does perm ease do?
brings lactose across cell membrane
Upon infecting a new host bacterial cell, what happens to the new genes?
can be inserted into the recipient cell's genome
Organisms with mutations that are beneficial in their environment can
can readily adapt, survive, and reproduce - these mutations are the basis of changes in populations (evolution)
Genomes include
chromosomes w/DNA + the DNA in mitochondria/chloroplasts and/or plasmids
Guanine always binds to
cytosine with 3 hydrogen bonds
Providing variety
differences in the order of bases responsible for variable traits and unique qualities of each organism
induced mutations result from
exposure to known mutagens
Chromosomes are subdivided into
genes
structural genes
genes that code for proteins
regulatory gene
genes that control gene expression
example of genotype
genes that express blue eye color
All types of genes constitute the genetic makeup
genotype
Mutations leading to nonfunctional proteins are
harmful; possible fatal
what does b-galactosidase do?
hydrolyzes lactose
example of catabolic operon
if the substrate lactose (a sugar) is present, bacteria induces the operon that codes for the synthesis of lactase; lactase is the enzyme that catalyzes the breakdown of lactose.
Lactose Operon is which class of operons?
inducible
RNA primer
is synthesized at the origin of replication (short strand of RNA that serves as a starting point for adding nucleotides)
what is semiconservative?
it preserves the exact sequence of genes in the original parent molecule, because each chromosome ends up with one new strand of DNA and one old strand.
Eukaryotic chromosomes are
multiple and linear
Genetic recombination
occurs when an organism acquires and expresses genes that originated in another organism
Lac Operon is normally off or on?
off: -In the absence of lactose, transcription is blocked so that genes encoding the enzymes are not active
Viral genome
one or more pieces of DNA or RNA; generally contains only genes needed for production of new viruses
mRNA is transcribed from
only one strand of DNA, the template strand, which contains the gene
The expression of the genotype creates observable traits
phenotype
DNA polymerase
proofreads nucleotides during DNA replication
DNA complexed with
protein constitutes the genetic material as chromosomes
Spontaneous mutations
random change in the DNA due to errors in replication that occur without known cause
Transformation is a useful tool for what?
recombinant DNA technology (genes from humans and other organisms can be inserted into a plasmid and then introduced into bacteria through transformation; as the bacteria reproduces, it replicates its entire genome, including the new plasmid, before dividing into two new daughter cells. Using this recombination technique, many copies of a gene can be made.)
DNA replication is what?
semiconservative
E. coli (gene size)
single chromosome containing 4,288 genes and is 1 mm in length
what may happen during assembly of new viruses?
some of the viral assemblies may take up one of the host cell's DNA fragments instead of the viral DNA or RNA
Genome
sum total of genetic material, including both DNA and the chromosomal structures that package the DNA within a cell
Substrate
the reactant molecule(s) that an enzyme binds to, causing a reaction and forming products
Genetics
the study of heredity
Adenine binds to
thymine with 2 hydrogen bonds
conjugation
transfer of a plasmid or chromosomal fragment (DNA) from a donor cell to a recipient cell via a direct connection (pilus)
what does b-galactosidase transacetylase do?
uncertain function
what is selection pressure?
when the environment selecting one feature over another in favor of survival and enhanced reproduction
Any change in genes that confers an advantage during selection pressure
will more likely be retained by the population, and passed on to offspring.
Maintenance of code during reproduction
Constancy of base pairing guarantees that the code will be retained
how does regulation of protein synthesis work in prokaryotes?
by operons
Helicase
(enzyme) unwinds and unzips the DNA double helix
Inducible
(induction) operon is turned ON by the presence of the substrate: -catabolic operon -substrate
from DNA to Protein
1. A protein's primary structure determines its shape and function 2. Proteins determine phenotype. Living things are largely what their proteins make them. 3. DNA is mainly a blueprint that tells the cell which kinds of proteins to make and how to make them.
3 means for genetic recombination in bacteria
1. Conjugation 2. Transformation 3. Transduction
2 types of operons
1. inducible 2. Repressible
Significance of DNA Structure
1.Maintenance of code during reproduction 2.Providing variety
The science of genetics explores
1.Transmission of biological traits from parent to offspring 2.Expression and variation of those traits 3.Structure and function of genetic material 4.How this material changes
Three basic categories of genes
1.structural genes 2.Genes that code for RNA 3. regulatory genes
regulation of protein synthesis and metabolism
Genes are regulated to be active only when their products are required (In other words, we only want to transcribe and translate a gene when the protein it codes for is needed.)
nontemplate strand
The other complementary DNA strand (opposite of the template strand).
what is DNA
Two strands twisted into a double helix
