Ap Biology Chapter 16: The Molecular Basis Of Inheritance Flashcards
What are the two chemical components of chromosomes?
DNA and protein.
What are the two chemical components of bacteriophages?
Simple protein/protective coat and DNA.
Why did researchers originally think that protein was the genetic material?
Proteins were classified as a class of macromolecules with great heterogeneity and specificity of function. Had the requirements for heredity material.
Distinguish between the virulent and nonvirulent strains of Streptococcus pneumoniae studied by Frederick Griffith
Pathogenic: disease causing - S Nonpathogenic: R cells.
What was the purpose of Griffith's studies?
Testing whether a genetic trait can be transferred between different bacterial strains.
Summarize Griffith's experiment.
Griffith experimented with different strains of pneumonia bacteria, S (lethal) and R (harmless). When he injected mice with S strain bacteria, the mice died. When he injected mice with R strain bacteria, they lived. However, when he injected mice with heat-killed S strain bacteria (not lethal anymore), they lived. When he injected mice with heat-killed S strain bacteria and live R strain bacteria, the mice died.
Define transformation:
Change in genotype and phenotype due to assimilation of external DNA by a cell.
Explain the approach of the Oslwald Avery experiment. What was the transforming factor?
They took DNA, RNA, and protein, applied specific treatments that inactivated each, and tested each sample for its ability to transform live nonpathogenic bacteria; DNA.
What are the components of bacteriophage?
Head, tail sheath, tail fiber, and DNA.
What is a bacteriophage?
A virus that infects bacteria.
Polymerase can start its own strand - true or false?
False. Primers are needed so polymerase can expand upon it.
What is RNase?
Degrades RNA primers.
How does a bacteriophage destroy a bacterial cell?
1. Tail fibers bind to specific receptor sites on outer surface.2. Sheath of cell contracts, injecting the phage DNA into the cell; cell's DNA is hydrolyzed3. Phage DNA synthesizes phage proteins and copies of phage genome by host enzymes4. Assembly of phage inside bacteria5. Release - enzymes that damages the cell wall are made, allowing for fluid to enter, causing the cell to burst, releasing the phage.
How did Hershey and Chase "label" DNA and viral proteins? explain their experiment.
Tagged proteins with radioactive sulfur because of the disulfide bonds. Tagged DNA with radioactive phosphorous bc of phosphates in the DNA. Found that T2 (phage) DNA entered the cell but phage protein did not.
What are Chargaff's rules?
1. Base composition varies between species.2. A = T and C = G.
What are the three components of a nucleotide?
phosphate group, deoxyribose sugar, nitrogenous base.
Who built the first model of DNA and discovered its double helix shape?
Watson and Crick. Franklin found the double helix by using x-ray crystallography, which led Watson to approximate the width of the helix and the spacing of the of the nitrogenous bases.
Distinguish between pyrimidines and purines:
Purines: A and G - 2 organic rings Pyrimidines: C and T - single rings
How did Watson and Crick's model explain the basis for Chargaff's rules?
A can form 2 hydrogen bonds with T, and T only, and G can form a 3 hydrogen bond with C, and C only.
Is Adenine a purine or pyrimidine? In DNA, RNA, or both?
Purine and both.
Is Guanine a purine or pyrimidine? In DNA, RNA, or both?
Purine and both.
Is Thymine a purine or pyrimidine? In DNA, RNA, or both?
Pyrimidine and DNA only.
Is Uracil a purine or pyrimidine? In DNA, RNA, or both?
Pyrimidine and RNA.
Is Cytosine a purine or pyrimidine? In DNA, RNA, or both?
Pyrimidine and both.
What holds two base pairs together?
Hydrogen bonds.
What holds the backbone (sugar and phosphate) of DNA together?
Phosphodiester bonds.
A + G = ?
T + C.
Explain what is meant by the 5' and 3' ends of the nucleotide.
Direction of the DNA. New strand of DNA starts from end of 3'.
What is meant by the description "antiparallel" regarding the strands that make up DNA?
Subunits from 2 sugar-phosphate backbones run in opposite directions to each other, allowing for base pairing. One funds 5' to 3' top to bottom, and the other has a 5' on the bottom and a 3' on top.
What is the semiconservative model of replication?
Replicated double helix consists of one old strand, which was derived from the old parent molecule, and one newly made strand (compliment).
Who lead to the elucidation that the correct mechanism of DNA replication is semiconservative?
Meselson and Stahl.
What is the conservative DNA replication method?
2 parent molecules reassociate after acting as templates.
What is the dispersive method of DNA replication?
Each strand of both daughter molecules contain a mixture of old and newly synthesized DNA.
Explain the Meselson and Stahl experiment.
E. Coli was grown in a 15N medium, the bacteria was transferred to a "lighter" N14 medium, DNA sample was centrifuged, a second centrifuge later occurred, creating a second generation. The first replication in the 14N medium produced a band of hybrid (15N-14N) DNA, eliminating the possibility of a conservative model. Second replication produced a light and hybrid DNA, supporting a semi-conservative. Their actual data collected followed what should have happened in the semi-conservative model. C: Light and heavy bandSC: Light and hybridD: only hybrid
Define the origins of replication:
short stretches of DNA having a specific sequence of nucleotides. Prokaryotes have one, eukaryotes have many.
What is the difference between the leading and lagging strands during DNA replication?
Lagging: DNA strand elongated away from the replication fork (moving away from helicase). Not synthesized continuously, creating Okazaki fragments. Leading: Following right behind helicase.
What is the direction of synthesis of the new strand of DNA?
Nucleotides are added to the 3' end of the pre-existing chain.
What are Okazaki fragments? How are they welded together?
Segments of lagging strand. Ligase joins the strands together.
Which enzyme holds DNA strands apart?
single-strand binding proteins.
Which enzyme adds DNA molecules to new strand?
DNA polymerase III.
Which enzyme relives strain caused by unwinding?
Topoisomerase.
Which enzyme joins DNA fragments together?
DNA ligase.
Which enzyme removes RNA primer and replaces with DNA?
DNA polymerase I.
Describe DNA replication - use all of the enzymes!
1. Helicase unwinds DNA.2. Topoisomerase takes strain off DNA.3. Single-strand binding proteins hold the DNA strands apart.4. Primase creates RNA primer.5. Polymerase III adds nucleotides continuously on the leading strand from the 5' to 3' direction, tailing the helicase. 6. Lagging strand RNA is synthesized discontinuously by DNA p. III. 5/6: RNA primer serves to act as the starting point at which nucleotides of DNA are added afterwards, continuing the new strand. Starting point.7. DNA p. I removes the RNA, replacing it with DNA nucleotides.8. Ligase binds strand bits together. Binds ends of 3' to end of 5'.
What is the role of DNA polymerase in DNA proofreading and repair?
Removes incorrectly paired nucleotides and resumes synthesis.
What is the role of nuclease in DNA proofreading and repair?
Cuts out segments of DNA containing damage.
What is the role of ligase in DNA proofreading and repair?
Fills gaps caused by nuclease and seals the free DNA end of new DNA to old.
What is the role of repair enzymes in DNA proofreading and repair?
Find and repair damaged DNA.
What is a thymine dimer?
Covalent linking of thymine bases that are adjacent on a DNA strand.
What are telomeres?
Multiple repetitions of one short nucleotide sequence at tips of chromosomes.
Explain telomere erosion and role of telomerase:
1. Prevents staggered ends of daughter molecule from activating the cell's system for monitoring DNA damage (staggered ends can lead to cell death). 2. Buffer zone against organism's gene shortening. Postpone erosion of genes near ends of chromosomes.
Why are most cancer cells immortal, but most body cells have a limited life span:
Telomerase catalyzes the lengthening of telomeres in eukaryotic germ cells, thus restoring the original length by using its own RNA molecule as a template to extend the leading strand.Normal shortening may protect from cancer by limiting the number of divisions that somatic cells can undergo. Short telomeres = many divisions, but telomerase activity is high in cancerous cells.
Differentiate between heterochromatin and euchromatin.
E: dispersed chromatin makes DNA accessible for transcriptionH: Compacted interphase chromatin.
What attribute of DNA is most crucial to its accurate duplication?
Specific base pairing through hydrogen bonds.
At each end of a DNA replication bubble is __________.
Replication fork.
Unlike prokaryotic DNA replication, replication of eukaryotic chromosomes __________.
Cannot be completed by DNA polymerase - Eukaryotic chromosomes are linear, so extreme 3' end cannot be reached.