Exam 2: Ch 8 Part 1: Microbial Genetics

Question 1

Chromosome

Answer 1

discrete cellular structure made of a neatly packaged DNA molecule

Question 2

Eukaryotic chromsomes

Answer 2

DNA wound around histones
located in the nucleus
diploid (pairs; 2n; all of our cells except our sex cells) or haploid (single; 1n)
linear appearance

Question 3

Prokaryotic chromosomes

Answer 3

DNA condensed into a packet by means of histone-like proteins
single circular chromosome (1n)

Question 4

Genome

Answer 4

sum total of genetic material of an organism
Most of the genome exists in the form of chromosomes
Some appear as plasmids or in certain organelles of eukaryotes
Genome of cells: composed entirely of DNA
Genome of viruses: can contain either DNA or RNA

Question 5

Gene

Answer 5

a segment of DNA that contains the necessary code to make a protein or RNA molecule
3 categories:
-Structural: code for proteins
-Regulatory: control gene expression
-Genes that code for RNA machinery in protein production

Question 6

Genotype

Answer 6

an organism’s genetic makeup

its entire complement of DNA

Question 7

Phenotype

Answer 7

the expression of the genes
the proteins of the cell and the properties they confer on the organisms
size, shape, color, environment

Question 8

Nucleotide

Answer 8

basic unit of DNA structure
covalently bond to each other in a sugar-phosphate linkage
3 parts:
-Phosphate 
-Deoxyribose sugar
-Nitrogenous base

Question 9

Nitrogenous bases and base pairing

Answer 9

pairing dictated by the formation of hydrogen bonds btwn bases

Question 10

Complimentary base pairing

Answer 10

if sequence of one strand is known, sequence of other strand is inferred

Question 11

Antiparallel arrangement (of the double helix)

Answer 11

one side of the helix runs in the opposite direction of the other (one from 5’ to 3’, and other from 3’ to 5’)
significant factor in DNA synthesis and protein production

Question 12

DNA replication

Answer 12

involves unwinding a DNA double helix and using each strand as a template for a new complimentary strand
semi conservative – since each new chromosome will have one “old” and one “new” strand

Question 13

4 things needed to replicate DNA

Answer 13

1. Original DNA template
2. Nucleotides – a pool of nucleotides is free floating in the cytoplasm
3. Enzymes – DNA polymerase, ligase
4. Energy – ATP

Question 14

DNA polymerase

Answer 14

required to successfully replicate a single strand of DNA

Question 15

DNA replication in prokaryotes

Answer 15

Certain enzymes unwind the DNA → then DNA polymerase can read the parent strand and attach a complementary nucleotide to the new strand of DNA
Nucleotides are free in the cytoplasm of prokaryotes (free in the nucleoid region of eukaryotes)

Question 16

DNA vs RNA

Answer 16

RNA:
contains ribose instead of deoxyribose
Is single stranded
There is no T in RNA (instead it is a U → A:U in RNA)
can assume secondary and tertiary levels of complexity, leading to specialized forms of RNA (tRNA and rRNA)

Question 17

Transcription

Answer 17

DNA → RNA

copying, not changing the DNA or the language

Question 18

What are the 4 things needed for RNA synthesis?

Answer 18

1. Original DNA template – chromosome w/a promoter site (DNA sequence indicating start site) and a terminator site
2. Nucleotides – G, C, A, U – Uracil is substituted for thymine
3. Enzymes – RNA polymerase
4. Energy – ATP

Question 19

RNA polymerase

Answer 19

large, complex enzyme that directs the conversion of DNA into RNA

Question 20

Template strand

Answer 20

only one strand of DNA that contains meaningful instructions for synthesis of a functioning polypeptide

Question 21

Types of RNA (mRNA, tRNA, rRNA, regulatory)

Answer 21

1. Messenger RNA (mRNA) – RNA molecule that serves as a message of the protein to be produced
2. Transfer RNA (tRNA) – transfers amino acids to ribosome
3. Ribosomal RNA (rRNA) – forms the ribosome
4. Regulatory RNA – micro RNAs, anti-sense RNAs, riboswitches, small interfering RNAs

Question 22

Initiation

Answer 22

Initiate – need RNA polymerase (the running down of RNA polymerase, recognizing the promoter and starting this process)

RNA polymerase: recognizes promoter region → begins its transcription at a special sequence (the initiator) → As the DNA helix unwinds → it moves down the DNA synthesizing RNA molecule

when RNA polyermase hits the terminator sequence = whole thing will stop and close up

Question 23

Elongation

Answer 23

During elongation the mRNA is built → assembled by adding nucleotides that are complimentary to the DNA template → proceeds in the 5’ to 3’ direction → as elongation continues → the part of the DNA already transcribed is rewound into its original helical form

Question 24

Termination

Answer 24

The polymerase recognize another code that signals the separation and release of the mRNA strand/transcript

Question 25

Translation

Answer 25

mRNA → Protein changing the language from nucleotide to amino acid occurs at the ribosome the green mRNa strand is threaded thru the ribosome the ribosome "Reads" the mRNA strand codons with the help of the genetic code and tRNA

Question 26

Codons

Answer 26

groups of 3 mRNA molecules

Question 27

tRNA

Answer 27

decoder molecule which serves as a link to translate the RNA language into a protein language One site of the tRNA has an ANTICODON which complements the codon of mRNA The other site of the tRNA has an amino acid attachment site corresponding to a specific amino acid as noted in the genetic code

Question 28

Translation and the GENETIC CODE

Answer 28

Triplet code that specifies a given amino acid We use the “genetic code” to translate mRNA nucleotide sequence (codons) into amino acid sequence which make up proteins The “genetic code” is degenerate which allows for a certain amount of mutation (more than one genetic code can code for one amino acid) There is one start codon (AUG) that codes for the amino acid methionine There are 3 stop codons (UAA, UAG, UGA) that signal the ribosome to stop translation and let go of the polypeptide chain (protein)

Question 29

Translation at ribosome level

Answer 29

− Initiation – ribosomes bind mRNA near the start codon; tRNA anticodon with attached amino acid binds to the start codon − Elongation – ribosomes move along to the next codon, allowing a new tRNA to bind and add another amino acid; two amino acids form peptide bonds − Termination – stop codon terminates translation

Question 30

Polyribosomal complex

Answer 30

a single mRNA is long enough to be fed thru more than one ribosome Permits the synthesis of hundreds of protein molecules from the same mRNA transcript Would not see this in eukaryotes

Question 31

Transcription/translation for eukaryotes is similar to prokaryotes, except:

Answer 31

AUG encodes for a different form of methionine Transcription and translation are not simultaneous in eukaryotes Eukaryotes must splice out introns to achieve a mature mRNA strand to go to the ribosome Introns can have regulatory RNA that regulate the mRNA of the exons; they also often developed from insertion of transposons

Question 32

Operons (& gene regulation)

Answer 32

Only found in bacteria Coordinated set of genes to make proteins that are needed at the same time All regulated as a single unit Either inducible or repressible

Question 33

lac operon

Answer 33

When lactose is absent: the repressor block RNA polymerase from binding to the operator and transcribing downstream genes When lactose is present: it binds to the receptor and it falls off the operator allowing RNA polymerase to bind The downstream genes are responsible for digesting lactose and are only on when lactose is present

Question 34

Phase variation

Answer 34

bacteria turn on or off a complement of genes that leads to obvious phenotypic changes New environment = new phenotype! Most often traits affecting the bacterial cell surface

Question 35

Mutations

Answer 35

a change in the sequence of DNA Possible effects of mutations: -No effect → no change in amino acid sequence -Good → new amino acid sequence; increases variability in the gene pool = evolution -Bad → new amino acid sequence (cancer can be the product of a combo of bad mutations) – making the protein unable to work (cancer can be the product of a combination of bad mutations)

Question 36

Mutagen

Answer 36

chemical or radiation that brings about mutations | mutagen mutations rate is 10-1000x the normal mutation rate

Question 37

Point mutation

Answer 37

a base is substituted in the DNA - may or may not change the amino acid Put the cat out → puc the cat out Put the cat out → put

Question 38

Frameshift

Answer 38

the addition, deletion or insertion of one or more nucleotides drastically changes the amino acid sequence reading frame of mRNA shifts Put the cat out → put hec at out

Question 39

Thymine dimers caused by radiation

Answer 39

radiation, such as X-rays and UV rays can cause dimers to form in DNA; thymine dimers can interfere with DNA replication, transcription and translation

Question 40

Ames test

Answer 40

uses bacteria to identify possible mutagens by looking for mutations to occur; once a mutagen is identified, it is tested on animals to test if it is a carcinogen