BIO1003 – Quiz 2 Review

Flashcards reviewing quiz logistics, format, and content topics covering Unit 5 (Cell Division - Mitosis) and Unit 6 (DNA Structure and Function) for BIO1003 Quiz 2.

What is Interphase and how much time do cells spend in it?

Stage of the cell cycle where a cell prepares for division by growing and duplicating its DNA. (The cell is not dividing) Most cells are in interphase 90% of the time.

What happens during the G1 phase (Gap 1), what is chromatin, and how long does it last?

During the G1 phase, the cell grows in size, produces RNA, and synthesizes proteins. Chromatin is the complex of DNA and proteins found in the nucleus that condenses to form chromosomes during cell division. The duration of G1 phase varies depending on the cell type. It can last hours to days

What happens during the S phase (Synthesis) regarding DNA and chromatids?

During S phase, DNA is replicated, resulting in the duplication of chromatids, which are the two identical halves of a chromosome. This phase ensures that each daughter cell receives an identical set of DNA during division.

Does the cell grow during S phase, and how long does it last?

Cell growth continues. Duration - 8 to 10 hours

What happens during the G2 phase (Gap 2) and how long does it last?

Occurs after DNA replication. Final growth and preparation for mitosis. Duration: 5 hours.

What is the G0 phase and what is an example of a cell in this state?

A resting, non-dividing state where cells exit the cell cycle temporarily or permanently. Example: Nerve cells.

What is cell division made of, and what specifically is mitosis?

Cell division consists of two processes: mitosis and cytokinesis.

Mitosis definition: The division of the nucleus.

4 Phases: Prophase, Metaphase, Anaphase, Telophase (PMAT)

What are the 4 key events that happen during Prophase?

First stage of mitosis.

Centrioles move to opposite poles.

Mitotic spindle fibers begin to form.

DNA condenses into visible chromosomes and the nuclear envelope breaks down.

What happens during Metaphase, and where do chromosomes align?

Spindle fibers attach to chromosome centromeres.

Chromosomes align at the cell equator (metaphase plate).

Nuclear envelope is absent/broken down previously.

What happens to sister chromatids during Anaphase, and what happens to the shape of the cell?

Sister chromatids separate and are pulled to opposite poles by spindle fibers. The cell begins to elongate.

What 3 events occur during Telophase?

Chromosomes uncoil into chromatin. Nuclear envelope reforms. Spindle fibers disassemble.

What is cytokinesis, when does it begin, and how does it divide the cell?

Definition: Cytoplasm divides into two cells (division of the cytoplasm).

When it starts: Cytokinesis begins during telophase.

What divides: Division of cytoplasm, organelles, and cell membrane.

Mechanism: Contractile ring of microfilaments forms at the midline.

Result: Cell is pinched into two daughter cells.

Where do checkpoints occur, what signals control them, and what happens if DNA damage is detected?

Occur throughout the cell cycle; DNA is checked for errors and mutations. Controlled by internal and external signals (stop or move forward cues). If DNA damage is detected: DNA is repaired if possible. Cell cycle is permanently arrested if repair fails, and apoptosis occurs if damage is severe.

What does the G1 checkpoint determine, what 3 factors does it assess, and where do failing cells go?

• Determines: Whether the cell proceeds to S phase.

• Assesses: Cell size, nutrients, and DNA integrity.

• Failing cells: Cells that do not pass enter G0

What do the G2 and M (spindle) checkpoints check, and when does the M checkpoint occur?

• G2 Checkpoint: Determines readiness to enter mitosis; confirms DNA replication is complete and accurate.

• M Checkpoint (Spindle Checkpoint): Occurs during metaphase; ensures chromosomes are properly attached to spindle fibers and triggers exit from M phase and entry into G1.

What are the 2 types of regulatory genes, when does normal cell division occur, and what happens if these genes are damaged?

• Proto-oncogenes: Stimulate cell division.

• Tumor suppressor genes: Inhibit cell division.

• Normal Regulation: Cell division occurs only for growth and repair.

• If regulatory genes are damaged: Apoptosis is triggered.

Where are chromosomes found, what are they made of, and what is a gene?

• Location: Found in the nucleus.

• Composition: Each chromosome is made up of DNA (genetic instructions) and histones (support and gene control).

• Gene: A segment of DNA that controls protein synthesis (proteins = cell structure and function).

What is chromatin, what is its appearance, and when is it found in the cell?

• Composition: Made up of DNA and histones.

• Appearance: Loosely coiled, thin, thread-like appearance.

• Timing: Found in the nucleus between cell divisions (during Interphase).

What is DNA packing, and how do chromosomes differ structurally from chromatin during cell division?

• DNA Packing: DNA + histones coiled tightly during cell division.

• Chromosomes: Contain the same DNA and histones as chromatin, but are tightly coiled, condensed, thicker, and easier to see.

• Timing: Present during cell division (Mitosis).

Briefly distinguish between chromatin, a chromosome, and a sister chromatid.

• Chromatin: Uncoiled, loose DNA + histones (used between divisions).

• Chromosome: Tightly coiled, condensed DNA + histones (used during division).

• Sister Chromatid: One of two identical copies of a replicated chromosome joined at the centromere (formed in S phase).

What is a karyotype, how many total chromosome pairs are in a human cell, and how are they divided?

• Karyotype: An individual's complete set of chromosomes in a cell showing chromosome number and appearance; reveals chromosomal abnormalities.

• Total Pairs: 23 total pairs (46 total chromosomes).

• 22 Pairs (Autosomes): Control most inherited traits.

• 1 Pair (Sex Chromosomes): Determine biological sex.

What are the sex chromosome combinations for a genetic female vs. a genetic male?

• XX: Genetic female.

• XY: Genetic male.

How many chromosomes do somatic cells have versus germ cells, and how are they arranged?

• Somatic Cells (body cells): Almost all cells in the body have 46 chromosomes.

• Germ Cells (egg and sperm): The exception (contain half).

• Arrangement: Chromosomes are arranged in 23 pairs, one set from each parent.

What are homologous chromosomes and where does each chromosome in the pair come from?

• Chromosomes occur in matching pairs called homologous chromosomes.

• One chromosome is inherited from the mother, and one chromosome is inherited from the father.

What is the difference between diploid and haploid cells, and which cells in the body belong to each group?

• Diploid (2n): Two sets of chromosomes, one from each parent. All body cells are diploid (except sperm and egg).

• Haploid (n): Cell with an unpaired set of chromosomes (23 chromosomes). Sperm and egg cells are haploid.

How are genes arranged on homologous chromosomes in diploid cells?

• Genes occur in pairs.

• Each pair is found at the same position (locus) on a homologous chromosome.

What are the 3 components that make up a DNA nucleotide?

• Phosphate group

• Deoxyribose sugar (5-carbon sugar)

• Nitrogenous base (Adenine, Thymine, Guanine, or Cytosine)

What is complementary base pairing, what are the base pair rules, what bonds hold them together, and what is their function?

• Complementary Base Pairing: DNA pairs in a specific pattern to ensure accurate DNA structure and copying.

• Base Pair Rules: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C). These pairs always match the same way.

• Bonds: Base pairs are held together by hydrogen bonds (strong enough for stability, weak enough to separate during replication).

• Function: The order of bases stores genetic information (different sequences create different traits, acting as the biological genetic code of the cell).

What is the purpose of complementary base pairing and the order of nitrogenous bases in DNA?

• Complementary Pairing: Ensures accurate DNA structure and copying.

• Order of Bases: Stores genetic information (different sequences create different traits and act as the biological genetic code of the cell).

What is the function of the nucleus, what does DNA stand for, and how many genes do humans have?

• Nucleus: Cell's control center; contains genetic instructions, directs protein production, and houses chromosomes.

• DNA: Deoxyribonucleic acid.

• Genes: Stores genetic instructions (22,000 genes in humans; determines individual traits). Each DNA strand is 2 m long.

What is a nucleosome, what shape does DNA resemble, and what makes up a nucleotide?

• Nucleosome: Histone wrapped in DNA helix.

• Shape: Resembles a ladder; double-stranded molecule twisted into a double helix.

• Nucleotide: Repeating unit that makes up each side and half-rung of the ladder. Contains:

  1. Phosphate group

  2. Deoxyribose sugar

  3. Nitrogenous base (A, T, G, or C)

What forms the outer rails of the DNA ladder, and what does "antiparallel" mean?

• Sugar-Phosphate Backbone: Forms outer rails; provides structure and stability to the molecule.

• 5' and 3' Ends: Named based on carbon positions in the sugar molecule.

• Antiparallel: Strands run in opposite directions ($5' to 3'$ opposite $3' to 5'$).

What are telomeres, what is their function, why do they shorten, and how do they affect cell lifespan?

• What they are: Repeating DNA sequences found at the ends of chromosomes.

• Function: Act as protective caps, preventing damage to important genes during DNA replication.

• Why they shorten: During replication, a small section of DNA cannot be copied, causing telomeres to shorten with each cell division.

• Effect on cell lifespan: As telomeres become shorter, cells lose their ability to divide effectively, contributing to cell aging, limited cell lifespan, and driving human aging.

When does DNA replication occur, what is the result, and what does semi-conservative mean?

• Timing: Occurs during the S phase of interphase before a cell divides.

• Process: Double helix unwinds and separates; each original strand serves as a template.

• Semi-Conservative: Each new DNA molecule contains one original (conserved) strand and one newly synthesized daughter strand.

• Genome: The complete set of DNA; replication ensures it is copied accurately and consistently.

Where does replication begin, what forms, and what enzyme separates the DNA strands?

• Site: Begins at a specific site called the origin of replication.

• Structure: The DNA opens into a replication fork.

• DNA Helicase: Separates the two strands, temporarily exposing/untwisting the nucleotide bases so they can be copied.

What are the roles of Primase and DNA Polymerase during Elongation, and in what direction is DNA built?

• Primase: Adds short RNA primers in the 5' to 3’ direction to provide a starting point for DNA synthesis.

• DNA Polymerase: Attaches to the primer and adds nucleotides using base pairing rules (A-T, G-C).

• Direction: DNA Polymerase builds the new strand strictly in the 5' to 3’ direction.

Why is the leading strand built continuously while the lagging strand is built in Okazaki fragments?

• Leading Strand: Oriented so DNA polymerase moves forward smoothly, adding nucleotides continuously as the correct 5' to 3' direction is exposed.

• Lagging Strand: Cannot be copied continuously because DNA polymerase can only build 5' to 3'.

• Okazaki Fragments: Short segments of DNA made on the lagging strand that are later joined together.

What enzyme connects Okazaki fragments, and what happens as nucleotides are added?

• DNA Ligase: Connects the Okazaki fragments to form one continuous DNA strand on the lagging side.

• Termination: As nucleotides are added, the DNA becomes double-stranded and naturally twists back into its double helix shape, producing two identical DNA molecules.