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Micro Ch. 9 - genetics and genes


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the study of heredity
what does genetics explore?
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

sum total of genetic material of an organism

chromosomes + mitochondria / chloroplasts and / or plasmids

where is the genome of cells?
where is the genome of viruses
in DNA or RNA but never both
genetic material made up of DNA complexed with protein
what are bacterial chromosomes like?
single and circular loops
what are eucaryotic chromosomes like?
multiple and linear
the fundamental unit of heredity responsible for a given trait

make up chromosomes

what does a gene do?
provides information for a certain cell function

as a segment of DNA it also contains the necessary code to make a protein or RNA molecule

what are the three basic categories of genes?
1. genes that code for proteins - structural genes

2. genes that code for RNA

3. Genes that control gene expression - regulatory genes

genes are on ______.

chromosomes are in ________.
the cell
all types of genes constituting the genetic makeup
the expression of the genotype creating observable traits
how many genes do the smallest viruses have?
4-5 genes
what are the genome of E.coli like?
single chromosome containing 4,288 genes


1,000 times longer than a cell

what is the genome of human cells like?
46 chromosomes containing 31,000 genes

6 feet

180,000 times longer than the cell

what is the basic unit of DNA structure?
a nucleotide
what are the 3 parts of a nucleotide?
1. a 5 carbon sugar - deoxyribose

2. a phosphate group

3. a nitrogenous base - adenine, guanine, thymine, cytosine

how do nucleotides make up the backbone of a DNA helix?
nucleotides covalently bond to form a sugar phosphate linkage
what are the base pairs and bond types that make up the strands of DNA?
adenine binds to thymine with 2 hydrogen bonds

guanine binds to cytosine with 3 hydrogen bonds

what constitutes the DNA code?
the order of the bases
what is the significance of DNA structure?
1. maintenance of code during reproduction-constancy of base pairing guarantees that the code will be retained

2. providing variety -order of bases is responsible for unique qualities of each organism

how many different enzymes are involved in duplicating DNA?
okazaki fragments
broken up pieces of DNA
why is DNA replication considered semi-conservative?
because each chromosome ends up with one new strand of DNA and one old strand
each triplet of nucleotides on the RNA specifies a particular ______.
amino acid
proteins determine____.
what is DNA a blueprint for?
telling the cell which kinds of proteins to make and how to make them
single stranded molecules made of nucleotides
what is the makeup of RNA
5 carbon sugar - ribose

4 nitrogen bases - adenine, uracil, guanine, cytosine


what are the three types of RNA?
1. messenger RNA -mRNA
messenger RNA

carries DNA message through complementary copy

the message is in triples called codons

transfer RNA

made from DNA

secondary structure creates loops
bottom loop exposes a triplet of nucleotides called anticodon which designates specifically and complements mRNA

carries specific amino acids to ribosomes

ribosomal RNA

component of ribosomes where protein synthesis occurs

how does translation elongation occur?
1. a second tRNA with the complementary anticodon fills the A site of the ribosome

2. a peptide bond is formed between the amino acids

3. the first tRNA is released and the ribosome slides down to the next codon

4. another tRNA fills the A site and a peptide bond is formed

*this process continues until a stop codon is encountered.

how does translation termination occur?
since UAA, UAG, and UGA are termination codons for which there is no corresponding tRNA, when this codon is reached, the ribosome falls off and the last tRNA is removed from the polypeptide
what is the master genetic code? and how is it represented?
the message in messenger RNA, represented by the mRNA codons and the amino acids they specify
the master genetic code is ____ and_____.
universal and redundant
what do polyribosomal complexes allow for?
the synthesis of many protein molecules simultaneously from the same mRNA molecule.
do eucaryotic transcription and translation occur simultaneously?
where does eucaryotic transcription occur?
in the nucleus
where does eucaryotic translation occur?
the cytoplasm
what is the eucaryotic start codon?

*but does not use formyl-methionine

compared to bacterial mRNA, how many proteins does a eucaryotic mRNA encode?
a single protein, unlike bacterial mRNA which encodes many
intervening sequences of noncoding DNA
what has to happen to the introns that eucaryotic DNA contain?
they have to be spliced out of the final mRNA transcript
what makes up a viral genome?
one or more pieces of DNA or RNA

contains only genes needed for production of new viruses

what are the 6 steps of viral multiplication?
1. adsorption
2. penetration
3. uncoating
4. synthesis
5. assembly
6. release

when are genes regulated to be active?
only when their products are required
a set of genes, all of which are regulated as a single unit
in procaryotes how are genes regulated?
by operons
what are the two types of operons?
inducible and repressible
inducible operon
operon is turned ON by substrate
-catabolic operons - enzymes are needed to metabolize a nutrient are produced when needed

repressible operon
genes in a series are turned OFF by the product synthesized
-anabolic operon - enzymes used to synthesize an amino acid stop being produced when they are not needed
what type of operon is a lactose operon?
what three segments make up a lactose operon?
1. regulator- gene that codes for repressor

2. control locus - composed of promoter and operator

3. structural locus - made of 3 genes each coding for an enzyme needed to catabolize lactose

what are the three genes that make up the structural locus for lactose operons? what is their function?
beta galactosidase - hydrolyzes lactose

permease - brings lactose across cell membrane

beta galactosidase transacetylase - function is uncertain

when is the lac operon normally off? what is happening?
in the absence of lactose
the repressor binds with the operator locus and blocks transcription of downstream structural genes
when is the lac operon on? what is happening?
when lactose is present
the binding of lactose to the repressor protein changes its shape and causes it to fall off the operator

RNA polymerase can bind to the promoter

structural genes are transcribed

when is the only time a lac operon is able to function?
in the ABSENCE of glucose
what type of operon is an arginine operon?
is the arginine operon usually on or off? when will it do the opposite?
it is normally on and will be turned off when nutrient is no longer needed
how does the arginine operon turn off?
when excess arginine is present, it binds to the repressor and changes it. then the repressor binds to the operator and blocks arginine synthesis
which antibiotics affect transcription and translation?
Actinomycin D

how does Rifamycin affect transcription and translation?
it binds to RNA polymerase
how does Actinomycin D affect transcription and Translation?
binds to DNA and halts mRNA chain elongation
how does erythromycin and spectinomycin affect transcription and translation?
they interfere with attachment of mRNA to ribosomes
how do chloramphenicol, linomycin and tetracycline affect transcription and translation?
they bind to ribosome and block elongation
how does streptomycin affect transcription and translation?
it inhibits peptide initiation and elongation
a change in phenotype due to a change in genotype
wild type or wild strain
a natural, non mutated characteristic
mutant strain
an organism that has a mutation
what are the characteristics of a mutant strain?
they show variance in morphology, nutritional characteristics, genetics, control mechanisms, resistance to chemicals, etc.
what are two types of causes of mutations?
spontaneous and induced
spontaneous mutations
random change in the DNA due to errors in replication that occur without known cause
induced mutation
results from exposure to known mutagents, physical (primarily radiation), or chemical agents that interact with DNA in a disruptive manner
point mutation
addition, deletion or substitution of a few bases
missense mutation
causes changes in a single amino acid
nonsense mutation
changes a normal codon into a stop codon
silent mutation
alerts a base but does not change the amino acid

when expressed it changes the protein

back - mutation
when a mutated gene reverses to its original base composition
frameshift mutation
when the reading frame of the mRNA is altered by the addition or deletion of nucleotides in a newly synthesized DNA
bad guys like teratogens
what are some of the enzymatic repair mechanisms DNA has for mutations?
DNA polymerase
Mismatch repair
Light repair
Excision repair

how does DNA polymerase help repair mutations?
it proofreads nucleotides during DNA replication
how does mismatch repair help repair damaged DNA?
locates and repairs mismatched nitrogen bases that were not repaired by DNA polymerase
how does light repair help repair damaged DNA from mutations?
it helps repair DNA from UV light damage
how does excision repair work in helping damaged DNA?
it locates and repairs incorrect sequence by removing a segment of the DNA and then adding the correct nucleotides.
any compound known to be mutagenic
what test screens agricultural, industrial and medicinal compounds?
Ames test
indicator organism of the Ames Test
Salmonella typhimurium that has lost the ability to synthesize histidine
what are the positive effects of mutations?
any change that creates an advantage during selection pressure will be retained by the population

organisms with mutations that are beneficial in their environment can readily adapt, survive and reproduce

what are the negative effects of mutations?
mutations leading to nonfunctional proteins are harmful, and possibly fatal
when does genetic recombination occur?
when an organism acquires and expresses genes that originated in another organism
3 means for genetic recombination in bacteria
1. conjugation
2. transformation
3. transduction

transfer of a plasmid or chromosomal fragment from a donor cell to a recipient cell via a direct connection
what do gram -negative cell donors have?
a fertility plasmid (F plasmid, F factor) that allos the synthesis of a conjugation (sex) pilus
recipient cell of conjugation
a related species or genus without a fertility plasmid
how does conjugation happen?
a donor transfers fertility plasmid to recipient through a pilus
in conjugation, what happens to a portion of the chromosome and portion of the fertility plasmid?
they are transferred to the recipient
chromosome fragments from a lysed or burst cell are accepted by a recipient cell

the genetic code of the DNA fragment is acquired by the recipient

do donor and recipient cells have to be related in transformation?
bacteriophage serves as a carrier of DNA from a donor cell to a recipient cell
what are the two types of transduction?
generalized and specialized
generalized transduction
RANDOM fragments of disintegrating host DNA are picked up by the phage during assembly

any gene can be transmitted this way

specialized transduction
a highly SPECIFIC part of the host genome is regularly incorporated into the virus
specialized DNA segments that have the capability of moving from one location in the genome to another

"jumping genes"

what do transposons or "jumping genes" do?
cause rearrangement of the genetic material
in which ways can transposons or "jumping genes" move?
can move from one chromosome site to another

from a chromosome to a plasmid

from a plasmid to a chromosome

are transposons or "jumping genes" beneficial or harmful?
can be either

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