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Questions and Answers
What is the role of DNA helicase during DNA replication?
What is the role of DNA helicase during DNA replication?
Which enzyme connects Okazaki fragments during DNA replication?
Which enzyme connects Okazaki fragments during DNA replication?
In what direction does DNA polymerase synthesize new DNA strands?
In what direction does DNA polymerase synthesize new DNA strands?
What is the primary role of messenger RNA (mRNA) in gene expression?
What is the primary role of messenger RNA (mRNA) in gene expression?
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Where does transcription occur in the cell?
Where does transcription occur in the cell?
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What is a function of transfer RNA (tRNA) during protein synthesis?
What is a function of transfer RNA (tRNA) during protein synthesis?
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How do certain chemotherapeutic drugs affect DNA replication?
How do certain chemotherapeutic drugs affect DNA replication?
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What is the result of effective DNA replication in a cell?
What is the result of effective DNA replication in a cell?
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What was one of the key qualities of genetic material before modern discoveries?
What was one of the key qualities of genetic material before modern discoveries?
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Who was the first to discover the genetic role of DNA?
Who was the first to discover the genetic role of DNA?
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What characteristic of DNA allows it to be accurately replicated?
What characteristic of DNA allows it to be accurately replicated?
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What type of bacteria did Frederick Griffith study to understand the genetic role of DNA?
What type of bacteria did Frederick Griffith study to understand the genetic role of DNA?
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What aspect of DNA was primarily determined by biochemists in the mid-twentieth century?
What aspect of DNA was primarily determined by biochemists in the mid-twentieth century?
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What conclusion can be drawn about DNA's ability to be transmitted?
What conclusion can be drawn about DNA's ability to be transmitted?
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Which statement regarding the characteristics of DNA is incorrect?
Which statement regarding the characteristics of DNA is incorrect?
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What did the research efforts in mid-twentieth century molecular biology lead to?
What did the research efforts in mid-twentieth century molecular biology lead to?
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What is the consequence of inheriting a faulty code for enzyme EB?
What is the consequence of inheriting a faulty code for enzyme EB?
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How does androgen insensitivity affect physical development?
How does androgen insensitivity affect physical development?
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Which types of cancer are mentioned as the deadliest in the U.S.?
Which types of cancer are mentioned as the deadliest in the U.S.?
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What initiates carcinogenesis according to the information provided?
What initiates carcinogenesis according to the information provided?
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What role do tumor suppressor genes and proto-oncogenes play?
What role do tumor suppressor genes and proto-oncogenes play?
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What key function does the p53 tumor suppressor gene serve?
What key function does the p53 tumor suppressor gene serve?
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What is a consequence of mutations in transcription factors?
What is a consequence of mutations in transcription factors?
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Which of the following best describes the nature of cancer development?
Which of the following best describes the nature of cancer development?
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What role does DNase play in the transformation of R strain bacteria?
What role does DNase play in the transformation of R strain bacteria?
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What did Avery and his co-investigators conclude about proteins and RNA based on their experiments?
What did Avery and his co-investigators conclude about proteins and RNA based on their experiments?
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Which of the following was a key finding of the Hershey-Chase experiments?
Which of the following was a key finding of the Hershey-Chase experiments?
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What is DNA composed of, as determined by Watson and Crick?
What is DNA composed of, as determined by Watson and Crick?
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In Avery's experiments, what did the large molecular weight of the transforming substance suggest?
In Avery's experiments, what did the large molecular weight of the transforming substance suggest?
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Why did Avery's team use protein-digesting enzymes in their experiments?
Why did Avery's team use protein-digesting enzymes in their experiments?
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What was labeled with 32P in the Hershey-Chase experiments?
What was labeled with 32P in the Hershey-Chase experiments?
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What do the three subunits of a DNA nucleotide consist of?
What do the three subunits of a DNA nucleotide consist of?
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What characterizes the promoter use in eukaryotic gene expression compared to prokaryotic gene expression?
What characterizes the promoter use in eukaryotic gene expression compared to prokaryotic gene expression?
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Which level of gene control involves mechanisms like DNA methylation and chromatin packing?
Which level of gene control involves mechanisms like DNA methylation and chromatin packing?
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What is the primary function of heterochromatin in eukaryotic cells?
What is the primary function of heterochromatin in eukaryotic cells?
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How does chromatin remodeling contribute to gene expression?
How does chromatin remodeling contribute to gene expression?
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What is a result of X-inactivation in mammalian females?
What is a result of X-inactivation in mammalian females?
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Why are heterozygous females described as mosaics?
Why are heterozygous females described as mosaics?
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What are euchromatin regions associated with?
What are euchromatin regions associated with?
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Which of the following best describes the overall control of eukaryotic gene expression?
Which of the following best describes the overall control of eukaryotic gene expression?
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Which components are required for the initiation of translation?
Which components are required for the initiation of translation?
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What is the role of tRNA during the elongation phase of translation?
What is the role of tRNA during the elongation phase of translation?
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During the elongation process, what occurs after the next tRNA is in place at the A site?
During the elongation process, what occurs after the next tRNA is in place at the A site?
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What energy contribution is important in the elongation process of translation?
What energy contribution is important in the elongation process of translation?
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What does translocation refer to during the elongation phase?
What does translocation refer to during the elongation phase?
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Which sites are present in the ribosome during translation?
Which sites are present in the ribosome during translation?
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What role do elongation factors play in translation?
What role do elongation factors play in translation?
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Which of the following accurately describes the tRNA at the P site during elongation?
Which of the following accurately describes the tRNA at the P site during elongation?
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Study Notes
DNA Structure and Gene Expression
- DNA, deoxyribonucleic acid, is the genetic material.
- DNA structure was determined in 1953 by James Watson and Francis Crick.
- DNA is a chain of nucleotides.
- Each nucleotide is composed of phosphoric acid, a pentose sugar (deoxyribose), and a nitrogen-containing base.
- Four possible bases in DNA are adenine (A), guanine (G), thymine (T), and cytosine (C).
- Two polynucleotide strands make up DNA's double helix.
- Strands are held together by hydrogen bonds between the complementary bases.
- Adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C).
- A purine (A or G) is always bonded to a pyrimidine (T or C).
- The DNA helix resembles a ladder.
- Sides of the ladder are sugar-phosphate backbones.
- Rungs of the ladder are complementary base pairs.
- The two DNA strands are antiparallel, oriented in opposite directions.
DNA Replication
- DNA replication is the process of copying a DNA double helix into two identical double helices.
- The double-stranded structure of DNA allows each original strand to serve as a template for a complementary strand.
- DNA replication is semiconservative.
- Each daughter DNA double helix consists of one new strand of nucleotides and one old strand conserved from the parent DNA molecule.
- Several enzymes and proteins participate in DNA replication.
- DNA helicase unwinds and "unzips" the DNA by breaking hydrogen bonds between paired bases.
- New complementary DNA nucleotides fit into place along separated strands by complementary base pairing.
- These nucleotides are positioned and joined by DNA polymerase.
- DNA polymerase uses each original strand as a template.
- DNA polymerase can only add new nucleotides to one chain.
- Leading strand follows DNA helicase
- Lagging strand is synthesized in Okazaki fragments.
- DNA ligase connects Okazaki fragments.
- Many chemotherapeutic drugs for cancer treatment stop replication, and therefore cell division.
Gene Expression
- Gene expression is the process of using a gene sequence to synthesize a protein.
- Relies on different types of RNA (ribonucleic acid): Messenger RNA (mRNA), Transfer RNA (tRNA), Ribosomal RNA (rRNA).
- Gene expression involves two processes: transcription and translation.
- Transcription takes place in the nucleus.
- A portion of DNA serves as a template for mRNA formation.
- Translation takes place in the cytoplasm.
- The sequence of mRNA bases determines the sequence of amino acids in a polypeptide.
- tRNA brings amino acids to the ribosome.
- mRNA is processed before leaving the nucleus in eukaryotic cells: addition of poly-A tail and a guanine cap, removal of introns and splicing of exons
Transcriptions (Details)
- During transcription, a gene (segment of DNA) serves as a template to produce an RNA molecule
- A segment of DNA serves as a template for mRNA.
- mRNA bases are complementary to those in DNA.
- Each three mRNA bases = codon (triplet code) for a certain amino acid.
- mRNA is processed before leaving the nucleus, removing introns, modifying ends.
- mRNA carries a sequence of codons to the ribosomes
Translation (Details)
- Translation: tRNAs bring attached amino acids to the ribosomes.
- tRNA anticodons pair with codons, causing sequencing of amino acids.
- The order of codons determines the order of tRNA entering the ribosome.
- Translation involves three steps: initiation, elongation, and termination.
Mutations and Cancer
- A gene mutation is a permanent change in the sequence of bases in DNA.
- Effects range from altered gene expression to complete protein inactivity.
- Germ-line mutations occur in sex cells and are passed to subsequent generations; some are responsible for cancer susceptibility.
- Somatic mutations, not passed to offspring, can also lead to cancer development.
- Cause of mutations can be spontaneous or induced by environmental influences like radiation, chemicals, etc.
- DNA repair enzymes work to keep mutation rate low.
- Transposons (jumping genes) are specific DNA sequences that move within or between chromosomes; can alter neighboring gene expression in new location.
- Point mutations involve a change in a single nucleotide; one type is a base substitution (one nucleotide replaced by another).
- Other point mutations are from insertions and/or deletions of nucleotides.
- Frameshift mutations (insertions or deletions) result in a completely new sequence of codons, often causing a nonfunctional protein.
- Nonfunctional proteins can have large effects on phenotype, especially enzyme proteins.
- Examples are PKU (phenylketonuria) and albinism.
- Cancer originates from a cell with an accumulating mutation that allows the cell to divide uncontrollably.
- Other factors like tumor suppressor genes and oncogenes can influence cancer development.
- p53 is frequently mutated in many types of human cancer and acts as a transcription factor to control genes, including cell cycle inhibitors.
- RB protein controls cyclin D gene expression and controls entry into S stage of cell cycle
- Cancer follows a multistep progression; usually begins as an abnormal, benign cell growth.
- Additional mutations can cause the growth to become malignant, meaning it is cancerous and able to spread
- Cancer cells are genetically unstable, do not correctly control cell cycle, lack specialization, and can escape cell death signals. These cells also may proliferate elsewhere in the body (metastasis).
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