Genetics – Microbiology Test Questions Flashcard

Heredity
the transmission of genetic information from an organism to its progeny (offspring).
Chromosomes
a circular (prokaryotes) or linear (eukaryotes) molecule of DNA and proteins that contains genes

DNA structure

arranged in a double helix
contains deoxyribose sugar and phosphate backbone
composed of nucleotides (A, T, C, G)
Antiparallel strand orientation
Strands are complementary

nucleotides

DNA- ATCG

RNA-AUCG

Genes

a segment of DNA specifying a particular product (usually a protein)

Alleles

 different variations of the same gene
Mutation
permanent alteration in DNA

 

Genetic information transfer

 

 the Central Dogma of molecular biology

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Replication
DNA synthesis; existing DNA used as a template to make new DNA

 

Transcription

 

RNA synthesis; existing DNA (genes) used as a template to make RNA (rRNA, mRNA, and tRNA).
Translation
Protein synthesis; RNA molecules are used to form proteins from amino acids
What Direction does DNA replication take place?
Always occurs in a 5’ to 3’ direction
What direction does the two replication forks move?
Bidirectionally (progress in two directions simutaneously)
What are required enzymes for DNA replication?

Gyrase
Helicase
DNA polymerase
Ligase

 

Gyrase

 

 unwinds the DNA double helix.

Helicase

“unzips” the two strands of DNA (breaking of hydrogen bonds that hold the strands together).
DNA polymerase
adds nucleotides to synthesize a new DNA strand (daughter strand) from the template strand (parental strand)

Ligase

 seals the “nick” where replication forks meet (adds the final phosphodiester bond).

 

Leading strand synthesis

replication is continuous because the replication fork is already moving in a 5’ à 3’ direction for the leading strand.

Lagging strand synthesis

 replication is discontinuous (via the synthesis of Okazaki fragments) because the replication fork is moving in a 3’ à 5’ direction for the lagging strand, which does not work for DNA polymerase.

RNA Synthesis- Transcription is catalyzed by this

 

RNA Polymerase

Promoter sequences

site on a gene where RNA polymerase binds and begins transcription

3 RNA types

 

ribosomal RNA (rRNA)
messenger RNA (mRNA)
transfer RNA (tRNA)

ribosomal RNA (rRNA): 

component of ribosomes

messenger RNA (mRNA)

template for protein synthesis

transfer RNA (tRNA)

brings amino acids to the ribosome for the growing polypeptide

 

Eukaryotic

 

genes contain introns that are excised
RNA synthesis in nucleus; protein synthesis in cytoplasm

Prokaryotic

no introns in genes
RNA and protein are synthesized in the cytoplasm

mRNA codons

determine the amino acid sequence of a protein.

tRNA anticodons – 

complementary to the codons of mRNA

A tRNA carrying an amino acid 

is “charged”. An uncharged tRNA is not bound to an amino acid.

rRNA 

component of ribosomes, which catalyze protein synthesis.

Ribosomes: Small

(30S) subunit

composed of 16S rRNA and 21 proteins

Ribosomes Large

(50S) subunit
composed of 5S rRNA, 23S rRNA, and 31 proteins

Enzyme Repression  

enzymes to metabolize a substrate are not made if the substrate is not present 

Enzyme Induction 

– enzymes to metabolize a substrate are made if the substrate is present.

Point mutations

Missense

Nonsense

Silent

Missense

base change results in a new codon that dictates a different amino acid.

Nonsense

: base change results in a stop codon that terminates translation.

 

Silent

: base change results in a new codon that does not change the amino acid.

 

Frameshift

caused by the deletion (–1)  or insertion (+1) of a base.
Causes of DNA mutations

Spontaneous errors during DNA replication

Chemical mutagens
base analogs – mimic nitrogenous bases
acridine derivatives – cause frameshifts

 

UV Radiation
causes thymine dimers

Start Codon
AUG
Stop Codon

UAA

UAG
UGA

Name three types of rRNA

16S

23S

5S

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