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Questions and Answers
Which of the following is NOT a level at which gene expression is regulated in eukaryotes?
Which of the following is NOT a level at which gene expression is regulated in eukaryotes?
The lac operon includes genes responsible for the hydrolysis of sucrose.
The lac operon includes genes responsible for the hydrolysis of sucrose.
False
What is the function of the i gene in the lac operon?
What is the function of the i gene in the lac operon?
It codes for the repressor of the lac operon.
In eukaryotic cells, the _____ helps RNA polymerase recognize start sites for transcription.
In eukaryotic cells, the _____ helps RNA polymerase recognize start sites for transcription.
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Match the following lac operon genes with their functions:
Match the following lac operon genes with their functions:
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What role does lactose play in the regulation of the lac operon?
What role does lactose play in the regulation of the lac operon?
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Eukaryotic gene expression is solely regulated by transcription factors.
Eukaryotic gene expression is solely regulated by transcription factors.
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What happens to the lac operon when glucose is present in the growth medium?
What happens to the lac operon when glucose is present in the growth medium?
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Which RNA polymerase is responsible for transcribing mRNA in eukaryotes?
Which RNA polymerase is responsible for transcribing mRNA in eukaryotes?
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In eukaryotes, primary transcripts are functional and ready for protein synthesis.
In eukaryotes, primary transcripts are functional and ready for protein synthesis.
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What process involves the removal of introns and the joining of exons in eukaryotic cells?
What process involves the removal of introns and the joining of exons in eukaryotic cells?
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RNA polymerase III is responsible for transcribing _______.
RNA polymerase III is responsible for transcribing _______.
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How many adenylate residues are typically added at the 3’-end of hnRNA during the tailing process?
How many adenylate residues are typically added at the 3’-end of hnRNA during the tailing process?
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Match the following RNA polymerases with their corresponding functions:
Match the following RNA polymerases with their corresponding functions:
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Alternative RNA splicing allows for the creation of multiple mRNA molecules from a single primary transcript.
Alternative RNA splicing allows for the creation of multiple mRNA molecules from a single primary transcript.
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What phenomenon is proposed to explain the low number of human genes compared to the high complexity of human proteins?
What phenomenon is proposed to explain the low number of human genes compared to the high complexity of human proteins?
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Which statement accurately describes the genetic code?
Which statement accurately describes the genetic code?
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Point mutations only involve changes in multiple base pairs.
Point mutations only involve changes in multiple base pairs.
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What are the three codons that function as stop codons?
What are the three codons that function as stop codons?
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Francis Crick postulated the presence of an ___ that reads the genetic code and binds to amino acids.
Francis Crick postulated the presence of an ___ that reads the genetic code and binds to amino acids.
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Match the following terms with their definitions:
Match the following terms with their definitions:
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Which of the following statements about tRNA is correct?
Which of the following statements about tRNA is correct?
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The genetic code is highly specific and differs across organisms.
The genetic code is highly specific and differs across organisms.
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What is the dual function of AUG in the genetic code?
What is the dual function of AUG in the genetic code?
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Study Notes
DNA: The Genetic Material
- DNA is the genetic material
- Bacteriophage φ×174 has 5386 nucleotides
- Bacteriophage λ has 48,502 base pairs (bp)
- Escherichia coli has 4.6 × 109 bp
- Human haploid DNA has 3.3 × 109 bp
DNA Structure
- Polynucleotide chain consists of three components:
- Nitrogenous base
- Pentose sugar (ribose in RNA, deoxyribose in DNA)
- Phosphate group
- Nitrogenous bases are of two types:
- Purines (Adenine, Guanine)
- Pyrimidines (Cytosine, Thymine in DNA, Uracil in RNA)
- N-glycosidic linkage connects a nitrogenous base to the 1' carbon of the pentose sugar, forming a nucleoside
- Examples of Nucleosides: Adenosine, Deoxyadenosine, Guanosine, Deoxyguanosine, Cytidine, Deoxycytidine, Uridine, Deoxythymidine
- Phosphoester linkage connects the phosphate group to the 5' carbon of the sugar, forming a nucleotide
- 3'-5' phosphodiester linkage connects nucleotides to create a polynucleotide chain
- Thymine is a 5-methyl uracil
DNA Structure (page 2)
- 3' end of a polynucleotide chain has a free hydroxyl group (-OH) attached to the 3' carbon of the deoxyribose sugar
- In RNA, the 2' carbon of the ribose sugar also has a hydroxyl group
- DNA has a sugar-phosphate backbone
- Nitrogenous bases project from the backbone in the 1 and 3 positions, and are perpendicular to the backbone
Chargaff's Rules
- Adenine = Thymine (A=T)
- Guanine = Cytosine (G=C)
- Adenine + Guanine = Thymine + Cytosine (A+G = T+C)
Double Helix Model of DNA Structure
- DNA consists of two polynucleotide chains wound around each other to form a double helix
- Sugar-phosphate backbones are on the outside
- Nitrogenous bases are on the inside, paired through hydrogen bonds
- Base pairing: A with T, and G with C
- Pitch of helix: 3.4 nm
- Distance between base pairs: 0.34 nm
- Antiparallel polarity: Strands run in opposite directions
- Coiled in a right-handed fashion
Packaging of DNA Helix
- DNA is not scattered; it's held within a region termed the nucleoid in prokaryotes
- In eukaryotes, DNA is packaged with proteins called histones
- Histones have a positive charge that attracts the negatively charged DNA
- A nucleosome consists of DNA wound around an octamer of eight histone proteins
- Nucleosomes form a string of beads ("beads-on-a-string") that is further compacted into chromatin fibers
- Euchromatin: less dense; transcriptionally active
- Heterochromatin: more dense; transcriptionally inactive
The Search for Genetic Material
- 1928: Frederick Griffith identified a "transforming principle" in Streptococcus pneumoniae that could transform non-pathogenic bacteria into pathogenic ones
- 1952: Alfred Hershey and Martha Chase demonstrated that DNA is the genetic material of viruses
Properties of Genetic Material: DNA versus RNA
- DNA is more stable than RNA due to the presence of thymine instead of uracil at one of the bases
- RNA is more catalytic than DNA
- RNA was the first genetic material in essential life processes
History of DNA (page 5)
- DNA identified as an acidic substance in the nucleus in 1869 by Friedrich Miescher
The Hershey-Chase Experiment (page 6)
- Confirmed that DNA is the genetic material
Models of DNA Replication (page 8)
- Conservative model: Parental strands stay together; new strands bind together
- Semi-conservative model: Parental strands separate; each serves as a template to form a new strand
- Dispersive model: Pieces of old and new DNA are mixed in both new strands
The Machinery for DNA Replication (page 9)
- DNA replication is a costly process, utilizing deoxyribonucleotide phosphates
- DNA dependent DNA polymerase catalyzes the polymerization of deoxyribonucleotides using a DNA template
- DNA polymerase moves along a template strand and polymerizes in a 5' to 3' direction
- Synthesis of one strand is continuous; synthesis of other strand is discontinuous, creating Okazaki fragments
- DNA ligase joins the Okazaki fragments
Prokaryotic DNA Replication (page 10)
Proteins initiate replication, the strands separate, and replication proceeds in both directions until the entire molecule is copied creating replication 'bubbles'
Eukaryotic DNA Replication (page 10)
- Multiple replication origins lead to multiple replication bubbles that fuse together to speed up the replication process
Transcription (page 12)
- Transcription is the process of making RNA from a DNA template
- Involves RNA polymerase binding to a promoter, unwinding the DNA double helix, and synthesizing a complementary RNA sequence (follows base-pairing rules but replaces T with U)
- Elongation: RNA polymerase moves along DNA
- Termination: RNA polymerase reaches a termination sequence
Transcription Unit (page 12)
- Promoter: RNA polymerase binding site
- Structural gene: codes for a protein
- Terminator: Transcription termination signal
Eukaryotic Transcription (page 13)
- Eukaryotic cells have three types of RNA polymerases (I, II, and III)
- Transcription factors are needed along with RNA polymerase in eukaryotes
The Transcription Process (page 14)
- Initiation: RNA polymerase binds to the promoter
- Elongation: RNA polymerase moves along DNA, synthesizing RNA
- Termination: RNA polymerase reaches a termination sequence
RNA Processing (page 16)
- Primary transcripts (pre-mRNA) contain both exons and introns and are non-functional.
- Splicing: Removal of introns, joining exons to form mature mRNA.
- Capping: Addition of a modified nucleotide to the 5' end of pre-mRNA, making it stable
- Tailing: Addition of a string of adenine nucleotides to the 3' end of pre-mRNA, making it stable
Alternative RNA Splicing (page 16)
- Multiple mature mRNA molecules can be produced from a single pre-mRNA
- Different combinations of exons are created during splicing, increasing the number of proteins that a single gene can produce
Genetic Code (page 17)
- Three-base codons specify amino acids
- Codons code for specific amino acids
- Some codons act as stop signals, signaling the end of translation
tRNA—The Adapter Molecule (page 18)
- tRNA acts as translator to transfer amino acids from cytoplasm to ribosomes during translation
- tRNA has an anticodon loop that complements the codon on mRNA
Translation (page 19)
- Translation: the process of synthesizing a polypeptide using mRNA as a template in the ribosomes
- Initiation, elongation, and termination
- Amino acids are linked together to form a polypeptide chain following the instructions in mRNA
- Ribosomes catalyze the formation of peptide bonds
- Elongation: tRNA molecules deliver the appropriate amino acids and the ribosome adds them to the growing polypeptide chain until a termination codon is reached
- Termination: the process concludes once a stop codon is encountered
Regulation of Gene Expression (page 20)
- Genes are regulated, adjusting expression in response to internal and external factors to control production of proteins
- The availability of resources, cellular conditions, and external factors influence expression
- Regulation of genes varies with prokaryotes and eukaryotes
The Lac Operon (page 20)
- Lac operon is a set of genes involved in lactose utilization in bacteria.
- It consists of a regulatory gene (i gene) and three structural genes (z, y, and a genes)
- The i gene codes for the lac repressor protein
- The z gene codes for β-galactosidase, an enzyme that breaks down lactose
- The y gene codes for permease, a protein that transports lactose into the cell
- The a gene codes for transacetylase, involved in lactose metabolism
- Operon is turned off when lactose is absent, repressor binds to the operator preventing RNA polymerase from transcribing downstream genes; active repressor blocks RNA polymerase binding
- Operon is turned on when lactose is present, lactose binds to the repressor, inactivating it
- The repressor can't bind to the operator; RNA polymerase can transcribe the structural, Z, Y, A, genes; the protein products, which function in lactose utilization, are made
Human Genome Project (HGP) (page 22)
- Launched in 1990, aimed at mapping and sequencing the entire human genome
- 3 billion base pairs in the human genome
- Estimated to have 25,000 genes
Expressed Sequence Tags (ESTs) (page 22)
- ESTs are sequences of expressed genes, which are assigned to different functional categories
DNA Fingerprinting (page 23)
- Repetitive DNA regions are used to identify individuals
- Techniques include Southern blot hybridization using radio-labeled VNTR probes (Variable Number of Tandem Repeats)
CRISPR-Cas9 System (page 23)
- Gene editing technology
- Cas9 enzyme cuts DNA at specific sites
- Guide RNA directs the Cas9 enzyme to the target gene
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Description
Explore the essential concepts of DNA as the genetic material and delve into its intricate structure. Understand the components of a polynucleotide chain and the different types of nitrogenous bases involved. This quiz covers key facts about various organisms' DNA and the structural linkages that form nucleotides.
