Bisc 333 Exam 2 Questions And
Answers Latest Update | Solved
What is a gene? CORRECT ANSWERS Figuratively: the functional unit of genetic
information that specifies the structure of a protein
Literally: a segment of DNA coding a protein sequence
Multiple genes are kept on the chromosome.
How genetic information is used: CORRECT ANSWERS Replication
Transcription
Translation
Replication CORRECT ANSWERS DNA is copied
Transcription CORRECT ANSWERS -RNA molecule is synthesized from DNA template
-mRNA, tRNA, rRNA
Translation CORRECT ANSWERS -Genetic information in mRNA is converted into
protein sequence
-Genetic code
Genetic code CORRECT ANSWERS 3 bases = 1 amino acid
Nucleic acid backbone CORRECT ANSWERS Chain of alternating deoxyribose and
phosphate
Phosphate connects the 3' sugar to the 5' carbon of the next sugar
Nucleic acid synthesis CORRECT ANSWERS Chain is extended by adding a dNTP to
the free 3' hydroxyl end (with loss of diphosphate)
Goes in the 5' --> 3' direction
Nucleic acid properties CORRECT ANSWERS Molecule is very negative because of
the phosphates
Amphapathic - why DNA hates to be single stranded
Nucleosides CORRECT ANSWERS relatively hydrophobic
Double helix CORRECT ANSWERS Formed by two polynucleotide chains of DNA
Strands run antiparallel (5'-->3' and 3'-->5')
Strands complimentary bonded by hydrogen bonds
Base Pairing CORRECT ANSWERS A--T double bonds
G--C triple bonds (why this type is highly favored in bacteria is unknown)
,Double helix structure CORRECT ANSWERS The two strands of DNA are not
equidistant to each other
Spaces are called major/minor grooves
Major grooves of DNA CORRECT ANSWERS space large enough in the helix for a
protein to fit in and recognize the sequence by feeling the tops of the bases
Bacterial Genetic Elements CORRECT ANSWERS Chromosomes
Plasmids
Viral genomes
chromosomes CORRECT ANSWERS -Long, usually one, usually circular double-
stranded DNA
-Very few introns (non-spliceosomal introns and Group II self spacing)
-Very few repetitive sequences - almost all of the DNA is used in order to shorten the
DNA replication time length
plasmids CORRECT ANSWERS short, usually circular extrachromosomal double-
stranded DNA
viral genomes CORRECT ANSWERS when infected, DNA or RNA
Linear Bacterial Chromosomes CORRECT ANSWERS Hairpin End
Covalent 5' Protein Modification
These techniques are necessary to prevent double stranded exonucleases from
chewing away at the linear ends - meaning that it must adjust having to protect itself
from its own immune system
Hairpin End CORRECT ANSWERS folds back on itself to form a rounded end
Covalent 5' Protein Modification CORRECT ANSWERS covalently attaches a protein to
protect itself
Plasmids CORRECT ANSWERS "Small" extrachromosomal DNA molecules
Usually circular - linear ones are typically found in organisms with linear chromosomes
Organism can have none, one, or many kinds - depending on organism, strain, or
conditions can vary the copy number
Different mechanisms for plasmid segregation
Plasmid encoded genes usually not essential, but provide advantage under certain
conditions
-antibiotic resistance: can be transferred to help spread the resistance
-heavy metal resistance
-virulence: get this from a different source
Critical for molecular genetic research
,Restriction Modification Systems - aka immune system CORRECT ANSWERS Bacteria
generally don't want foreign DNA in their cells (viruses)
Many bacteria have Restriction endonucleases
Restriction endonucleases recognize specific palindromic (same forward and backward)
sequences
Endonuclease CORRECT ANSWERS cut DNA from inside the cell
Exonuclease CORRECT ANSWERS cut DNA from a free end
Restriction endonucleases CORRECT ANSWERS Cleave inside their sequence
Critical for molecular genetic research
Each has a cognate methylase
cognate methylase CORRECT ANSWERS Recognizes the same sequences as the RE
Modifies one of the bases chemically so the RE can't bind (usually adds a methyl)
Prevents cleavage of own DNA
Foreign DNA isn't modified and gets degraded
Semi-conservative DNA replication CORRECT ANSWERS After replication, you have a
new strand and an old strand
Meselson-Stahl Experiment CORRECT ANSWERS Proves that replication is semi-
conservative
1) Cells are grown on heavy Nitrogen. DNA is isolated, separated on a density gradient.
2) After 1 generation (2nd replication), on N14, all chromosomes are 15N/14N.
Replicating circular chromosomes CORRECT ANSWERS Two Hypotheses:
1. Rolling circle replication
2. Theta replication
Both of these hypotheses agree with Meselson-Stahl
Rolling circle replication CORRECT ANSWERS Makes a nick in the chromosome to
give it a free 3' end which opens up a place of replication to make a strand
For some phage genomes and some plasmid conjugation: doesn't stop after one copy
which generates a huge chain - this chain has multiple copies of the genome to be cut
up
Theta replication CORRECT ANSWERS Strands pull away from the edge of the circle
towards the inside to allow for replication
For bacterial chromosomes: starts with an origin of replication where proteins begin to
pull strands apart to create replication forks
Supercoiling CORRECT ANSWERS DNA twists on itself to come under torsion
Puts molecule under stress and to relieve this stress, it tightens on itself
Helical Pitch = base pair per turn
, Positive and Negative
DNA gyrase makes negative
Topoisomerase 1 removes negative
Positive supercoiling CORRECT ANSWERS increased winding
decreased helical pitch (fewer base pairs per turn)
If this is not relieved, it can stop DNA replication or break the DNA
Negative supercoiling CORRECT ANSWERS decreased winding
increased helical pitch
DNA gyrase CORRECT ANSWERS Makes negative supercoiling
Relieves the DNA molecule from the stress of positive supercoiling
Helpful for bacteria transcription because bacterial DNA are usually held at negative
supercoiling
Topoismerase I CORRECT ANSWERS Removes negative supercoiling
Helpful for bacterial balance
Replication fork CORRECT ANSWERS Single Strand Binding Proteins (SSBP)
RNA primer (primase)
DNA polymerase III
Okazaki fragments
DNA polymerase I
DNA Ligase
DNA polymerase III CORRECT ANSWERS Major elongation polymerase
High accuracy in correcting replication errors
3' exonuclease activity which can back up and fix errors
DNA polymerase I CORRECT ANSWERS degrades RNA primer and replaces with
DNA
DNA ligase CORRECT ANSWERS seals the breaks between the fragments (very
useful for genetic research)
Correcting Replication Errors CORRECT ANSWERS DNA Polymerase III
Endonucleases can repair errors after DNA synthesis
But, we don't always want these to be absolutely perfect
Termination of Replication CORRECT ANSWERS "Catenanes"
Decatenated by Topoisomerase IV
Polymerase Chain Reaction (PCR) CORRECT ANSWERS Select portions of DNA can
be artificially amplified
A single reaction cycle:
Answers Latest Update | Solved
What is a gene? CORRECT ANSWERS Figuratively: the functional unit of genetic
information that specifies the structure of a protein
Literally: a segment of DNA coding a protein sequence
Multiple genes are kept on the chromosome.
How genetic information is used: CORRECT ANSWERS Replication
Transcription
Translation
Replication CORRECT ANSWERS DNA is copied
Transcription CORRECT ANSWERS -RNA molecule is synthesized from DNA template
-mRNA, tRNA, rRNA
Translation CORRECT ANSWERS -Genetic information in mRNA is converted into
protein sequence
-Genetic code
Genetic code CORRECT ANSWERS 3 bases = 1 amino acid
Nucleic acid backbone CORRECT ANSWERS Chain of alternating deoxyribose and
phosphate
Phosphate connects the 3' sugar to the 5' carbon of the next sugar
Nucleic acid synthesis CORRECT ANSWERS Chain is extended by adding a dNTP to
the free 3' hydroxyl end (with loss of diphosphate)
Goes in the 5' --> 3' direction
Nucleic acid properties CORRECT ANSWERS Molecule is very negative because of
the phosphates
Amphapathic - why DNA hates to be single stranded
Nucleosides CORRECT ANSWERS relatively hydrophobic
Double helix CORRECT ANSWERS Formed by two polynucleotide chains of DNA
Strands run antiparallel (5'-->3' and 3'-->5')
Strands complimentary bonded by hydrogen bonds
Base Pairing CORRECT ANSWERS A--T double bonds
G--C triple bonds (why this type is highly favored in bacteria is unknown)
,Double helix structure CORRECT ANSWERS The two strands of DNA are not
equidistant to each other
Spaces are called major/minor grooves
Major grooves of DNA CORRECT ANSWERS space large enough in the helix for a
protein to fit in and recognize the sequence by feeling the tops of the bases
Bacterial Genetic Elements CORRECT ANSWERS Chromosomes
Plasmids
Viral genomes
chromosomes CORRECT ANSWERS -Long, usually one, usually circular double-
stranded DNA
-Very few introns (non-spliceosomal introns and Group II self spacing)
-Very few repetitive sequences - almost all of the DNA is used in order to shorten the
DNA replication time length
plasmids CORRECT ANSWERS short, usually circular extrachromosomal double-
stranded DNA
viral genomes CORRECT ANSWERS when infected, DNA or RNA
Linear Bacterial Chromosomes CORRECT ANSWERS Hairpin End
Covalent 5' Protein Modification
These techniques are necessary to prevent double stranded exonucleases from
chewing away at the linear ends - meaning that it must adjust having to protect itself
from its own immune system
Hairpin End CORRECT ANSWERS folds back on itself to form a rounded end
Covalent 5' Protein Modification CORRECT ANSWERS covalently attaches a protein to
protect itself
Plasmids CORRECT ANSWERS "Small" extrachromosomal DNA molecules
Usually circular - linear ones are typically found in organisms with linear chromosomes
Organism can have none, one, or many kinds - depending on organism, strain, or
conditions can vary the copy number
Different mechanisms for plasmid segregation
Plasmid encoded genes usually not essential, but provide advantage under certain
conditions
-antibiotic resistance: can be transferred to help spread the resistance
-heavy metal resistance
-virulence: get this from a different source
Critical for molecular genetic research
,Restriction Modification Systems - aka immune system CORRECT ANSWERS Bacteria
generally don't want foreign DNA in their cells (viruses)
Many bacteria have Restriction endonucleases
Restriction endonucleases recognize specific palindromic (same forward and backward)
sequences
Endonuclease CORRECT ANSWERS cut DNA from inside the cell
Exonuclease CORRECT ANSWERS cut DNA from a free end
Restriction endonucleases CORRECT ANSWERS Cleave inside their sequence
Critical for molecular genetic research
Each has a cognate methylase
cognate methylase CORRECT ANSWERS Recognizes the same sequences as the RE
Modifies one of the bases chemically so the RE can't bind (usually adds a methyl)
Prevents cleavage of own DNA
Foreign DNA isn't modified and gets degraded
Semi-conservative DNA replication CORRECT ANSWERS After replication, you have a
new strand and an old strand
Meselson-Stahl Experiment CORRECT ANSWERS Proves that replication is semi-
conservative
1) Cells are grown on heavy Nitrogen. DNA is isolated, separated on a density gradient.
2) After 1 generation (2nd replication), on N14, all chromosomes are 15N/14N.
Replicating circular chromosomes CORRECT ANSWERS Two Hypotheses:
1. Rolling circle replication
2. Theta replication
Both of these hypotheses agree with Meselson-Stahl
Rolling circle replication CORRECT ANSWERS Makes a nick in the chromosome to
give it a free 3' end which opens up a place of replication to make a strand
For some phage genomes and some plasmid conjugation: doesn't stop after one copy
which generates a huge chain - this chain has multiple copies of the genome to be cut
up
Theta replication CORRECT ANSWERS Strands pull away from the edge of the circle
towards the inside to allow for replication
For bacterial chromosomes: starts with an origin of replication where proteins begin to
pull strands apart to create replication forks
Supercoiling CORRECT ANSWERS DNA twists on itself to come under torsion
Puts molecule under stress and to relieve this stress, it tightens on itself
Helical Pitch = base pair per turn
, Positive and Negative
DNA gyrase makes negative
Topoisomerase 1 removes negative
Positive supercoiling CORRECT ANSWERS increased winding
decreased helical pitch (fewer base pairs per turn)
If this is not relieved, it can stop DNA replication or break the DNA
Negative supercoiling CORRECT ANSWERS decreased winding
increased helical pitch
DNA gyrase CORRECT ANSWERS Makes negative supercoiling
Relieves the DNA molecule from the stress of positive supercoiling
Helpful for bacteria transcription because bacterial DNA are usually held at negative
supercoiling
Topoismerase I CORRECT ANSWERS Removes negative supercoiling
Helpful for bacterial balance
Replication fork CORRECT ANSWERS Single Strand Binding Proteins (SSBP)
RNA primer (primase)
DNA polymerase III
Okazaki fragments
DNA polymerase I
DNA Ligase
DNA polymerase III CORRECT ANSWERS Major elongation polymerase
High accuracy in correcting replication errors
3' exonuclease activity which can back up and fix errors
DNA polymerase I CORRECT ANSWERS degrades RNA primer and replaces with
DNA
DNA ligase CORRECT ANSWERS seals the breaks between the fragments (very
useful for genetic research)
Correcting Replication Errors CORRECT ANSWERS DNA Polymerase III
Endonucleases can repair errors after DNA synthesis
But, we don't always want these to be absolutely perfect
Termination of Replication CORRECT ANSWERS "Catenanes"
Decatenated by Topoisomerase IV
Polymerase Chain Reaction (PCR) CORRECT ANSWERS Select portions of DNA can
be artificially amplified
A single reaction cycle:
