DNA Structure & Function and The Cell Cycle Review

Flashcards covering DNA structure and function, historical discoveries, DNA replication, the eukaryotic cell cycle, cell division, PCR, and DNA repair mechanisms, as presented in the lecture notes.

What is DNA composed of?

DNA is a polymer built of monomer subunits called nucleotides. Each nucleotide consists of a base (Adenine, Thymine, Guanine, Cytosine), a sugar (deoxyribose), and a phosphate group.

How many base pairs are in human DNA, and how many nucleotides total?

Human DNA consists of approximately 3 BILLION base pairs (3 Gbp), which means there are 6 billion nucleotides total.

What are the three main goals of the Human Genome Project (HGP)?

The three main goals were to determine the sequence of all bases, build 'maps' showing gene locations, and produce 'linkage maps' for tracking inherited traits.

What law was passed to address the societal implications of genetic information from the HGP?

The Genetic Information Nondiscrimination Act (GINA) was passed, which states that predictive genetic information may not be used in health insurance or in the workplace in the US.

What was Gregor Mendel's contribution to modern genetics?

Gregor Mendel laid the foundation for modern genetics through his work on hybrid varieties of English pea plants in 1866.

Who isolated 'nuclein' and was the first to demonstrate a specific molecule in the nucleus that was not protein?

Friedrich Miescher isolated 'nuclein' (phosphate-rich acidic compounds) from the nuclei of leucocytes in 1869.

What was Phoebus Levene's contribution to understanding DNA's chemical nature?

Phoebus Levene isolated the sugars of DNA and RNA, identified the four different DNA nucleotides, and established how nucleotides link together in chains. He also proposed the Tetranucleotide Hypothesis.

What did Frederick Griffith discover in his experiments with Streptococcus pneumonia?

Griffith discovered the 'transforming principle,' concluding that living 'R' bacteria had been transformed into pathogenic 'S' bacteria by an unknown heritable substance from dead S cells.

How did Avery, MacLeod, and McCarthy build upon Griffith's work?

Using an in-vitro model, they determined that DNA was the material transmitted from one generation to the next, demonstrating that transformation cannot occur unless DNA is present.

What are Chargaff's Rules?

Chargaff's Rules state that for each species, the percentage of Adenine (A) and Thymine (T) are about equal (A=T), and the percentage of Guanine (G) and Cytosine (C) are about equal (G=C).

Who definitively proved that DNA is the genetic material, and how?

Alfred Hershey and Martha Chase proved DNA as the genetic material in 1952 using bacteriophages, showing that phage DNA, not protein, enters the bacterial cell to direct replication.

What technique did Wilkins and Franklin use to study DNA, and what did it reveal?

Maurice Wilkins and Rosalind Franklin used X-ray crystallography to produce 'photo 51,' which clearly showed DNA's helical structure and suggested two antiparallel sugar-phosphate backbones with nitrogenous bases paired in the interior.

What did Watson and Crick propose about the structure of DNA?

James Watson and Francis Crick developed the double-helical model of DNA, proposing it consists of two polynucleotide strands in an antiparallel orientation with A paired to T (2 H-bonds) and C paired to G (3 H-bonds).

What did Meselson and Stahl demonstrate about DNA replication?

Matthew Meselson and Frank Stahl showed in 1958 that DNA replication is semi-conservative, meaning each of the two new daughter molecules has one old strand (from the parent) and one newly synthesized strand.

What are the two groups of nitrogenous bases, and which bases belong to each?

The two groups are Pyrimidines (Cytosine, Uracil, Thymine) and Purines (Adenine, Guanine).

How are the two polynucleotide strands of DNA linked together?

The two polynucleotide strands are held together by hydrogen bonds between the complementary nitrogenous bases (A with T, G with C).

What does it mean for DNA strands to be 'antiparallel' and 'directional'?

Antiparallel means the two strands run in opposite directions (one 3' to 5', the other 5' to 3'). Directional refers to the specific carbons (3' with hydroxyl, 5' with phosphate) on the sugar-phosphate backbone.

How is DNA packaged into a chromosome, from smallest to largest structure?

DNA is packaged in multiple levels: DNA strand → Nucleosome (DNA + histones) → 30 nm fiber → Looped domains (300 nm fiber) → Chromatid (700 nm fiber) → Replicated chromosome (1,400 nm).

What is the difference between euchromatin and heterochromatin?

Euchromatin is loosely packed chromatin, usually expressed. Heterochromatin is densely packed chromatin, usually not expressed.

What are the four reasons why cells need to reproduce?

Cells need to reproduce to make more organisms/cells, for damage repair, for growth and development, and for tissue renewal.

What is binary fission, and in which organisms does it occur?

Binary fission is the process of cell division in prokaryotes. It involves replication of circular DNA, attachment to the plasma membrane, elongation of the membrane, inward growth of the membrane, and cytokinesis to form two identical daughter cells.

What are the two major phases of the Eukaryotic Cell Cycle?

The two major phases are Interphase (normal growth and preparation for cell division) and the Mitotic Phase (replicated DNA and cytoplasm are split).

List the stages of Interphase and briefly describe what happens in each.

Interphase includes G1 phase (primary growth, organelle duplication, cell doubles in size), S phase (DNA replication, forming sister chromatids), and G2 phase (proteins, lipids, ribosomes made, organelles reproduce, DNA checked for damage, chromosomes condense). There is also a G0 phase for non-dividing cells.

Describe the role of DNA Polymerase III in DNA replication.

DNA Polymerase III adds nucleotides to the 3' end of the new growing strand, synthesizing the leading strand continuously and the lagging strand discontinuously in short Okazaki fragments.

What is the function of helicase and single-strand binding proteins (SSBs) in DNA replication?

Helicase unwinds the parental double helix at the replication forks. Single-strand binding proteins (SSBs) bind to and stabilize the unwound single-stranded DNA until it is used as a template.

What enzyme relieves the overwinding strain ahead of replication forks, and how?

Topoisomerase relieves overwinding strain by temporarily breaking, swiveling, and rejoining DNA strands, preventing supercoiling during unwinding.

Why is primase necessary for DNA replication?

DNA polymerases cannot initiate polynucleotide synthesis; they only add to existing 3' ends. Primase synthesizes a short RNA primer, providing a starting point for DNA Polymerase III to add DNA nucleotides.

Describe the roles of DNA Polymerase I and DNA ligase in DNA replication.

DNA Polymerase I removes RNA primers (synthesized by primase) and replaces them with DNA nucleotides. DNA ligase then joins the Okazaki fragments on the lagging strand, and the DNA that replaced the primer to the rest of the leading strand DNA.

What are the two main parts of the Mitotic Phase?

The Mitotic Phase is divided into Karyokinesis (mitosis, division of the nucleus) and Cytokinesis (division of the cytoplasm).

List the 5 stages of Mitosis in order.

The 5 stages of Mitosis are Prophase, Prometaphase, Metaphase, Anaphase, and Telophase.

What key event defines Anaphase during mitosis?

In Anaphase, cohesin proteins degenerate, allowing sister chromatids to separate and move toward opposite poles of the cell, becoming individual chromosomes.

How does cytokinesis differ between animal and plant cells?

In animal cells, cytokinesis involves the formation of a cleavage furrow that constricts the cytoplasmic mass. In plant cells, a cell plate forms in the middle and grows outward to divide the cell.

What are the three main stages of Polymerase Chain Reaction (PCR)?

The three main stages of PCR are Denaturation (DNA strands separate at high temperature), Annealing (primers attach to each DNA strand at lower temperature), and Elongation (dNTPs base-pair to each strand, and DNA polymerase extends them).

What is the formula for calculating exponential cell growth?

The formula for calculating exponential cell growth is Nt = N0(2^n), where Nt is the number of cells at time 't', N0 is the starting number of cells, and n is the number of generations.

What are the three internal checkpoints in the eukaryotic cell cycle, and what do they primarily check?

The three internal checkpoints are G1 (checks for cell size, reserves, genomic DNA damage, and favorable conditions), G2 (checks for adequate cell size, protein reserves, complete DNA replication, and undamaged DNA), and the Mitotic/Metaphase checkpoint (checks if all sister chromatids are correctly attached to spindle microtubules).

What is the difference between proto-oncogenes and tumor suppressor genes in relation to cancer?

Proto-oncogenes are normal genes that encode positive cell cycle regulators; when mutated, they become oncogenes, promoting uncontrolled cell division. Tumor suppressor genes encode negative cell cycle regulators that prevent uncontrolled division; when mutated, they are unable to stop the cell cycle.

Who was Henrietta Lacks, and what is the significance of HeLa cells?

Henrietta Lacks was a woman from whom the HeLa cell line, the oldest and most frequently used immortal human cell line, was obtained in 1951. HeLa cells have been pivotal in numerous scientific discoveries in cancer, AIDS, gene mapping, and virology.

How does environmental damage, specifically UV light, affect DNA?

UV light can cause thymine dimers, which are covalently bonded thymines (T=T). These dimers are highly disruptive for DNA replication.

Describe the process of Nucleotide Excision Repair (NER).

NER repairs mismatches by using nucleases to cut out and replace damaged stretches of DNA, followed by DNA polymerase replacing the removed nucleotides with correct ones, and DNA ligase sealing the gap.

What is the 'end replication problem' in eukaryotes, and why don't prokaryotes face it?

In eukaryotes, the linear DNA ends get shorter with each round of replication because the last RNA primer cannot be replaced with DNA. Prokaryotes do not have this problem because their DNA is circular.

What are telomeres, and what is their purpose?

Telomeres are repeating sequences of nucleotides (e.g., CCCTAA/TTAGGG) located on both ends of eukaryotic chromosomes. They postpone the erosion and loss of essential genes near the ends of DNA molecules and can be extended by telomerase.

What is telomerase, and in which cell types is it typically active?

Telomerase is an enzyme that catalyzes the lengthening of telomeres. It is active in certain cells and stages of life, such as during development, in germ cells (especially sperm), lymphocytes in bone marrow, and a subset of epithelial cells.