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Questions and Answers

What is the role of DNA helicase during DNA replication?

  • Adds nucleotides to the lagging strand
  • Unwinds the DNA double helix (correct)
  • Connects the sugar-phosphate backbone
  • Synthesizes Okazaki fragments

Which enzyme connects Okazaki fragments during DNA replication?

  • RNA polymerase
  • DNA ligase (correct)
  • DNA polymerase
  • Helicase

In what direction does DNA polymerase synthesize new DNA strands?

  • 3' to 5'
  • 5' to 3' (correct)
  • In both directions simultaneously
  • Randomly, based on nucleotide availability

What is the primary role of messenger RNA (mRNA) in gene expression?

<p>Serves as a template for protein synthesis (D)</p> Signup and view all the answers

Where does transcription occur in the cell?

<p>In the nucleus (D)</p> Signup and view all the answers

What is a function of transfer RNA (tRNA) during protein synthesis?

<p>Brings amino acids to the ribosome (D)</p> Signup and view all the answers

How do certain chemotherapeutic drugs affect DNA replication?

<p>They act as nucleotide analogs (B)</p> Signup and view all the answers

What is the result of effective DNA replication in a cell?

<p>Formation of identical double helix molecules (D)</p> Signup and view all the answers

What was one of the key qualities of genetic material before modern discoveries?

<p>It could store information for development. (D)</p> Signup and view all the answers

Who was the first to discover the genetic role of DNA?

<p>Frederick Griffith (B)</p> Signup and view all the answers

What characteristic of DNA allows it to be accurately replicated?

<p>Its ability to form double-stranded structures. (B)</p> Signup and view all the answers

What type of bacteria did Frederick Griffith study to understand the genetic role of DNA?

<p>Streptococcus pneumoniae (D)</p> Signup and view all the answers

What aspect of DNA was primarily determined by biochemists in the mid-twentieth century?

<p>The structure and formation of DNA. (B)</p> Signup and view all the answers

What conclusion can be drawn about DNA's ability to be transmitted?

<p>It is stable and transmitted with high accuracy. (C)</p> Signup and view all the answers

Which statement regarding the characteristics of DNA is incorrect?

<p>DNA can only be found in prokaryotic organisms. (D)</p> Signup and view all the answers

What did the research efforts in mid-twentieth century molecular biology lead to?

<p>Knowledge of DNA as genetic material. (C)</p> Signup and view all the answers

What is the consequence of inheriting a faulty code for enzyme EB?

<p>Inability to produce melanin (A)</p> Signup and view all the answers

How does androgen insensitivity affect physical development?

<p>Female secondary sexual characteristics develop in genetic males (D)</p> Signup and view all the answers

Which types of cancer are mentioned as the deadliest in the U.S.?

<p>Lung, colorectal, and breast cancer (B)</p> Signup and view all the answers

What initiates carcinogenesis according to the information provided?

<p>Loss of tumor suppressor gene activity (C)</p> Signup and view all the answers

What role do tumor suppressor genes and proto-oncogenes play?

<p>They control the activity of transcription factors. (A)</p> Signup and view all the answers

What key function does the p53 tumor suppressor gene serve?

<p>Controls genes that inhibit cell cycle progression (A)</p> Signup and view all the answers

What is a consequence of mutations in transcription factors?

<p>Potential contribution to cancer development (D)</p> Signup and view all the answers

Which of the following best describes the nature of cancer development?

<p>It is a result of accumulating mutations over time (C)</p> Signup and view all the answers

What role does DNase play in the transformation of R strain bacteria?

<p>It prevents transformation by digesting DNA. (C)</p> Signup and view all the answers

What did Avery and his co-investigators conclude about proteins and RNA based on their experiments?

<p>Neither proteins nor RNA are the genetic material. (A)</p> Signup and view all the answers

Which of the following was a key finding of the Hershey-Chase experiments?

<p>Viral DNA entered the bacteria while viral protein did not. (B)</p> Signup and view all the answers

What is DNA composed of, as determined by Watson and Crick?

<p>A chain of nucleotides. (B)</p> Signup and view all the answers

In Avery's experiments, what did the large molecular weight of the transforming substance suggest?

<p>It suggested that genetic variability exists. (A)</p> Signup and view all the answers

Why did Avery's team use protein-digesting enzymes in their experiments?

<p>To confirm that proteins are not genetic material. (D)</p> Signup and view all the answers

What was labeled with 32P in the Hershey-Chase experiments?

<p>Viral DNA. (A)</p> Signup and view all the answers

What do the three subunits of a DNA nucleotide consist of?

<p>Phosphoric acid, a pentose sugar, and a nitrogen-containing base. (B)</p> Signup and view all the answers

What characterizes the promoter use in eukaryotic gene expression compared to prokaryotic gene expression?

<p>Eukaryotic genes each have their own promoter. (B)</p> Signup and view all the answers

Which level of gene control involves mechanisms like DNA methylation and chromatin packing?

<p>Pretranscriptional control (A)</p> Signup and view all the answers

What is the primary function of heterochromatin in eukaryotic cells?

<p>To keep genes turned off (B)</p> Signup and view all the answers

How does chromatin remodeling contribute to gene expression?

<p>It pushes nucleosomes aside to allow DNA access. (B)</p> Signup and view all the answers

What is a result of X-inactivation in mammalian females?

<p>One X chromosome is randomly inactivated in a cell. (C)</p> Signup and view all the answers

Why are heterozygous females described as mosaics?

<p>They have patches of cells expressing different X chromosomes. (B)</p> Signup and view all the answers

What are euchromatin regions associated with?

<p>Active genes that are loosely packed. (D)</p> Signup and view all the answers

Which of the following best describes the overall control of eukaryotic gene expression?

<p>It occurs at multiple levels, providing diverse regulation. (D)</p> Signup and view all the answers

Which components are required for the initiation of translation?

<p>Small ribosomal subunit, mRNA, initiator tRNA, large ribosomal subunit (A)</p> Signup and view all the answers

What is the role of tRNA during the elongation phase of translation?

<p>To transfer amino acids and match anticodons to mRNA codons (D)</p> Signup and view all the answers

During the elongation process, what occurs after the next tRNA is in place at the A site?

<p>The peptide chain is transferred to the tRNA at the A site (D)</p> Signup and view all the answers

What energy contribution is important in the elongation process of translation?

<p>Energy contributes to peptide bond formation (B)</p> Signup and view all the answers

What does translocation refer to during the elongation phase?

<p>Movement of mRNA forward by one codon length (B)</p> Signup and view all the answers

Which sites are present in the ribosome during translation?

<p>A (amino acid) site, P (peptide) site, E (exit) site (B)</p> Signup and view all the answers

What role do elongation factors play in translation?

<p>They facilitate the binding of tRNA anticodons to mRNA codons (C)</p> Signup and view all the answers

Which of the following accurately describes the tRNA at the P site during elongation?

<p>It holds the growing peptide chain (A)</p> Signup and view all the answers

Flashcards

DNA's role

DNA is the genetic material that stores information for development, structure, and metabolism of a cell or organism, and is stable for replication and transmission to future generations.

DNA's stability

DNA has the property of maintaining its identity over generations, accurately replicating, and transmitting genetic information.

Griffith's experiment

A 1931 study that began to identify the role of DNA. Studied Streptococcus pneumoniae bacteria. Noticed different strains.

S strain

The smooth bacterial strain, with a capsule, in Griffith's pneumococcus experiment.

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Capsule in bacteria

A protective layer on certain bacterial strains like the Streptococcus pneumoniae (S strain).

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Genetic material

The substance that determines the traits and characteristics of an organism.

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Molecular biology

The study of life at the molecular level, including DNA.

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Streptococcus pneumoniae

A bacteria that causes pneumonia.

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DNA Replication

The process by which a DNA molecule is copied to produce two identical DNA molecules.

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Leading Strand

The new DNA strand synthesized continuously in the 5' to 3' direction, following the movement of DNA helicase.

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Lagging Strand

The new DNA strand synthesized discontinuously in short fragments (Okazaki fragments) in the 5' to 3' direction, moving away from DNA helicase.

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Okazaki Fragments

Short DNA fragments synthesized on the lagging strand during DNA replication.

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DNA Ligase

An enzyme that joins the Okazaki fragments together on the lagging strand, forming a continuous DNA molecule.

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Gene Expression

The process of using a gene sequence to synthesize a protein.

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Transcription

The process of copying a gene sequence from DNA into messenger RNA (mRNA) in the nucleus.

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Translation

The process of converting the mRNA code into a protein in the cytoplasm.

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Avery's Experiment

A series of experiments that identified DNA as the transforming principle. They used enzymes to remove proteins, RNA and DNA from the S strain bacteria and observed their effect on the R strain bacteria.

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Transforming Principle

The substance responsible for transferring genetic information from one organism to another. In Avery's experiment, it was proven to be DNA.

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Hershey-Chase Experiment

A groundbreaking experiment using radioactive labeling to confirm that DNA is the genetic material, not protein. It showed that DNA, not protein, enters bacteria during viral infection.

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Radioactive Labeling

Using radioactive isotopes to trace specific molecules, like DNA or protein, within an experiment. This technique was crucial in the Hershey-Chase experiment.

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Viral DNA

The genetic material of a virus. Viruses use host cells to replicate, so their DNA is injected into the cell.

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What did the Hershey-Chase experiment prove?

The Hershey-Chase experiment provided definitive proof that DNA, not protein, is the genetic material. It confirmed that DNA is the carrier of genetic information.

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What was the purpose of using DNase in Avery's experiments?

DNase, an enzyme that breaks down DNA, was used to see if the transforming factor was dependent on DNA. The results showed that DNase prevented transformation.

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Why was it important to use enzymes that digest protein in Avery's experiment?

Using protein-digesting enzymes allowed Avery and his team to determine whether protein was the transforming principle. Their results showed that it wasn't.

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Gene Expression Control

The process of regulating when, where, and how much a gene is expressed.

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Pretranscriptional Control

Regulation of gene expression before transcription, affecting whether a gene is expressed at all.

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Transcriptional Control

Regulation of gene expression at the transcription level, controlling the rate of mRNA production.

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Posttranscriptional Control

Regulation of gene expression after transcription, affecting the stability and translation of mRNA.

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Translational Control

Regulation of gene expression at the translation level, affecting the rate of protein synthesis.

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Posttranslational Control

Regulation of gene expression after translation, affecting protein activity.

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Heterochromatin

Densely packed chromatin where genes are generally inactive.

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Euchromatin

Loosely packed chromatin where genes are likely to be active.

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Initiation in Translation

The first stage of protein synthesis, where all components come together: the small ribosomal subunit, mRNA, initiator tRNA (carrying methionine), and the large ribosomal subunit.

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Initiator tRNA

A special tRNA that always carries the amino acid methionine and binds to the start codon (AUG) on mRNA during initiation.

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Ribosomal Binding Sites

The ribosome has three binding sites for tRNA: A (amino acid), P (peptide), and E (exit) sites. Each site plays a role in bringing tRNA to the ribosome.

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Elongation in Translation

The process by which the polypeptide chain grows longer, amino acid by amino acid.

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Elongation Factors

Proteins required during elongation, helping tRNA anticodons bind to mRNA codons at the ribosome.

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Peptide Bond Formation

The chemical reaction that connects amino acids together to form a long polypeptide chain.

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Spent tRNA

A tRNA molecule that has lost its attached amino acid and is no longer needed in protein synthesis.

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Faulty Enzyme EB

A non-functional enzyme preventing tyrosine from converting to melanin, leading to albinism.

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Androgen Insensitivity

A condition where cells are unresponsive to androgens like testosterone due to a faulty receptor, causing a genetic male to develop female external genitalia.

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Tumor Suppressor Genes

Genes that control cell division and prevent uncontrolled growth, acting as 'brakes' for cell proliferation.

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Proto-oncogenes

Genes that promote cell division and growth, acting as 'accelerators' for cell proliferation.

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p53 Gene

A major tumor suppressor gene that controls cell cycle inhibitors and promotes apoptosis.

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Carcinogenesis

The development of cancer, starting with a loss of tumor suppressor gene activity and/or gain of oncogene activity.

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Cell Cycle Inhibitors

Proteins that halt the cell cycle to prevent uncontrolled cell division.

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Apoptosis

Programmed cell death, a natural process that eliminates damaged or unnecessary cells, helping to prevent cancer.

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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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