Micro Ch. 9 - genetics and genes
Terms
undefined, object
copy deck
- genetics
- 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 - genome
-
sum total of genetic material of an organism
chromosomes + mitochondria / chloroplasts and / or plasmids - where is the genome of cells?
- DNA
- where is the genome of viruses
- in DNA or RNA but never both
- chromosomes
- 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
- genes
-
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
- chromosomes are in ________.
- the cell
- genotype
- all types of genes constituting the genetic makeup
- phenotype
- 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
1mm
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?
- 30
- 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____.
- phenotype
- what is DNA a blueprint for?
- telling the cell which kinds of proteins to make and how to make them
- RNA
- single stranded molecules made of nucleotides
- what is the makeup of RNA
-
5 carbon sugar - ribose
4 nitrogen bases - adenine, uracil, guanine, cytosine
phosphate - what are the three types of RNA?
- 1. messenger RNA -mRNA
- mRNA
-
messenger RNA
carries DNA message through complementary copy
the message is in triples called codons - tRNA
-
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 - rRNA
-
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?
- no.
- where does eucaryotic transcription occur?
- in the nucleus
- where does eucaryotic translation occur?
- the cytoplasm
- what is the eucaryotic start codon?
-
AUG
*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
- introns
- 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
- operons
- 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?
- inducible
- 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?
- repressible
- 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?
-
Rifamycin
Actinomycin D
Erythromycin
Spectinomycin
Chloramphenicol
Linomycin
Tetracycline
Streptomycin - 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
- mutation
- 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
- mutagens
- 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.
- carcinogenic
- 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 - conjugation
- 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
- transformation
-
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?
- no
- transduction
- 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
- transposons
-
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