BIMM 100 Midterm questions with
verified answers
Structure of DNA - correct answer ✔✔ -DNA/RNA are chains of nucleic acids
-5' to 3' directionality; phosphate at 5' end and hydroxyl group at 3' end
-Proposed by Watson and Crick
-Consists of two long helical strands that are coiled around a common axis to form a double
helix
-DNA strands composed of nucleotides (aka bases), which are A, T, C, and G.
EXPERIMENT: How do we know that DNA is the genetic material? - correct answer ✔✔ -The
Hershey-Chase Experiments
Used differential labeling --> used radioactive sulfur that only labeled protein (protein has sulfur
in cysteine and methionine; DNA doesn't have sulfur); DNA was labeled with radioactive
phosphorus
Phage released its genetic material into bacterium --> phage labeled with radioactive
phosphorus appeared in the cell
Chargaff's Rules - correct answer ✔✔ -#purines=#pyrimidines
-A=T and C=G but A+T does not equal C+G
Role of transcription factors - correct answer ✔✔ -DNA binding proteins that bind to specific
sequences of DNA and act as switches, either activating or repressing transcription of particular
genes
Structure of a nucleotide - correct answer ✔✔ -Phosphate group
-Pentose sugar (ribose in RNA and deoxyribose in DNA)
,-Nitrogenous base
Purines vs. pyrimidines - correct answer ✔✔ -Purines: adenine and guanine
-Pyrimidines: cytosine, thymine, and uracil
Central dogma - correct answer ✔✔ DNA -> RNA -> Protein
How can DNA be denatured? - correct answer ✔✔ -Increasing the temperature of a solution of
DNA --> hydrogen bonds break and strands separate
-Near the denaturation temperature, a small increase in the temperature causes a rapid loss of
the weak interactions holding the strands together
-Melting temperature (Tm) depends on several factors:
Molecules with greater proportion of G-C pairs require higher temperatures to denature
because of the three hydrogen bonds, which make them more stable than A-T
-Low ion concentration, agents that destabilize hydrogen bonds (formamide or urea), and
extremes of pH denature DNA at low Tm
-Low pH: bases are protonated (+ charged) and repel
-High pH: bases lose protons (- charged) and also repel
Melting temperature (Tm) - correct answer ✔✔ -Point where we think the DNA is half-
denatured
-As G-C pairs increase, Tm increases
How can we detect the denaturation of DNA? - correct answer ✔✔ -Based on the absorption of
260 nm light, you can tell if the DNA is single or double stranded because base pairing
interations (double stranded) don't absorb light, but the single strands do
Gene - correct answer ✔✔ The entire nucleic acid sequence that is necessary for the synthesis
of a functional product
, -Includes everything you need to make the gene product: coding region that gets translated,
transcribed non-coding regions, transcriptional control regions, splice sites, and polyA sites
Poly-A sites and splice sites - correct answer ✔✔ -Poly-A sites: sequences that specify 3'
cleavage and polyadenylation
-Splice sites: splicing of primary RNA transcripts
Introns vs. exons - correct answer ✔✔ -Exons: coding regions
-Introns: noncoding regions
-During transcription, the entire gene is copied into pre-mRNA (includes introns and exons), but
during the process of RNA splicing, introns are removed and exons joined to forma contiguous
coding sequence
Solitary vs. duplicated genes - correct answer ✔✔ -Solitary genes: roughly 25-50% of these
protein-coding genes are represented only once in the haploid genome; not found in any other
gene family
-Duplicated genes: constitute the second group of protein-encoding genes; they have close but
nonidentical sequences that often are located within 5-50 kb of one another; gene families
encode closely related proteins
ex. Hemoglobin: HBB and HBD evolve in adults that have a lower affinity for oxygen so that it
can deposit it into our tissues, while HBG1 and HBG2 are in fetuses and have a high affinity for
oxygen, stripping it from the mother's blood so the fetus can have a lot of oxygen
How can genes get duplicated? - correct answer ✔✔ 1. Unequal recombination- afforded by
repeat sequences scattered around our genome
Unequal crossing over leads to one chromosome with two β-globin genes and one chromosome
with none
2. Exon shuffling creates new genes
verified answers
Structure of DNA - correct answer ✔✔ -DNA/RNA are chains of nucleic acids
-5' to 3' directionality; phosphate at 5' end and hydroxyl group at 3' end
-Proposed by Watson and Crick
-Consists of two long helical strands that are coiled around a common axis to form a double
helix
-DNA strands composed of nucleotides (aka bases), which are A, T, C, and G.
EXPERIMENT: How do we know that DNA is the genetic material? - correct answer ✔✔ -The
Hershey-Chase Experiments
Used differential labeling --> used radioactive sulfur that only labeled protein (protein has sulfur
in cysteine and methionine; DNA doesn't have sulfur); DNA was labeled with radioactive
phosphorus
Phage released its genetic material into bacterium --> phage labeled with radioactive
phosphorus appeared in the cell
Chargaff's Rules - correct answer ✔✔ -#purines=#pyrimidines
-A=T and C=G but A+T does not equal C+G
Role of transcription factors - correct answer ✔✔ -DNA binding proteins that bind to specific
sequences of DNA and act as switches, either activating or repressing transcription of particular
genes
Structure of a nucleotide - correct answer ✔✔ -Phosphate group
-Pentose sugar (ribose in RNA and deoxyribose in DNA)
,-Nitrogenous base
Purines vs. pyrimidines - correct answer ✔✔ -Purines: adenine and guanine
-Pyrimidines: cytosine, thymine, and uracil
Central dogma - correct answer ✔✔ DNA -> RNA -> Protein
How can DNA be denatured? - correct answer ✔✔ -Increasing the temperature of a solution of
DNA --> hydrogen bonds break and strands separate
-Near the denaturation temperature, a small increase in the temperature causes a rapid loss of
the weak interactions holding the strands together
-Melting temperature (Tm) depends on several factors:
Molecules with greater proportion of G-C pairs require higher temperatures to denature
because of the three hydrogen bonds, which make them more stable than A-T
-Low ion concentration, agents that destabilize hydrogen bonds (formamide or urea), and
extremes of pH denature DNA at low Tm
-Low pH: bases are protonated (+ charged) and repel
-High pH: bases lose protons (- charged) and also repel
Melting temperature (Tm) - correct answer ✔✔ -Point where we think the DNA is half-
denatured
-As G-C pairs increase, Tm increases
How can we detect the denaturation of DNA? - correct answer ✔✔ -Based on the absorption of
260 nm light, you can tell if the DNA is single or double stranded because base pairing
interations (double stranded) don't absorb light, but the single strands do
Gene - correct answer ✔✔ The entire nucleic acid sequence that is necessary for the synthesis
of a functional product
, -Includes everything you need to make the gene product: coding region that gets translated,
transcribed non-coding regions, transcriptional control regions, splice sites, and polyA sites
Poly-A sites and splice sites - correct answer ✔✔ -Poly-A sites: sequences that specify 3'
cleavage and polyadenylation
-Splice sites: splicing of primary RNA transcripts
Introns vs. exons - correct answer ✔✔ -Exons: coding regions
-Introns: noncoding regions
-During transcription, the entire gene is copied into pre-mRNA (includes introns and exons), but
during the process of RNA splicing, introns are removed and exons joined to forma contiguous
coding sequence
Solitary vs. duplicated genes - correct answer ✔✔ -Solitary genes: roughly 25-50% of these
protein-coding genes are represented only once in the haploid genome; not found in any other
gene family
-Duplicated genes: constitute the second group of protein-encoding genes; they have close but
nonidentical sequences that often are located within 5-50 kb of one another; gene families
encode closely related proteins
ex. Hemoglobin: HBB and HBD evolve in adults that have a lower affinity for oxygen so that it
can deposit it into our tissues, while HBG1 and HBG2 are in fetuses and have a high affinity for
oxygen, stripping it from the mother's blood so the fetus can have a lot of oxygen
How can genes get duplicated? - correct answer ✔✔ 1. Unequal recombination- afforded by
repeat sequences scattered around our genome
Unequal crossing over leads to one chromosome with two β-globin genes and one chromosome
with none
2. Exon shuffling creates new genes
