Untitled Quiz

Structure of Chromatin

• Chromatin is the combination of DNA and histone proteins.
• DNA is coiled around histones to form nucleosomes, which then aggregate to form chromatin's thick, ropy fibers.

DNA Replication Timing

• Occurs before cell division to ensure each daughter cell receives a complete genome.

Chromosome Formation

• Chromosomes are formed only for DNA replication; otherwise, DNA exists as chromatin.

Semi-Conservative Replication

• Each new DNA strand contains one original strand and one new strand, ensuring fidelity in genetic information.

DNA Replication in Prokaryotes

• Prokaryotic DNA is circular and located in the cytoplasm, replicating from a single point in two directions simultaneously.
• Replication is faster in prokaryotes than in eukaryotes.

Replication Forks

• Origins of replication produce Y-shaped structures called replication forks, where new DNA strands are synthesized.

Eukaryotic DNA Replication

• In eukaryotes, DNA replication starts at hundreds of sites, forming multiple replication bubbles.

Helicase Function

• The helicase enzyme unwinds and separates DNA strands by disrupting hydrogen bonds.

Role of Single-Stranded Binding Proteins

• These proteins maintain the separation and stability of unwound DNA strands.

Primase Enzyme

• Primase synthesizes RNA primers necessary for the initiation of DNA synthesis, approximately 10 nucleotides long.

RNA Primer Replacement

• At the end of replication, RNA primers are removed and replaced with DNA nucleotides by DNA polymerase.

Functions of DNA Replication

• Adds new nucleotides, removes primers, and proofreads DNA for errors.

Direction of Nucleotide Addition

• New nucleotides are added at the 3' end of a growing DNA molecule, meaning synthesis occurs in the 5' to 3' direction.

Leading vs. Lagging Strands

• Leading strands are synthesized continuously towards the replication fork. Lagging strands are synthesized discontinuously, forming Okazaki fragments.

Okazaki Fragments

• Short segments on lagging strands synthesized in a direction opposite to overall replication; require ligase to seal them.

Proofreading Enzyme

• DNA polymerase checks for and corrects errors during DNA replication.

Excision Repair Enzyme

• Nuclease (or exonuclease) removes damaged DNA sections for repair.

Replication Speed

• Prokaryotes replicate DNA more rapidly than eukaryotes.

Chromatin vs. Chromosomes

• Chromatin consists of DNA wound around proteins, whereas chromosomes are tightly coiled chromatin.

Function of Telomeres

• Located at chromosome ends, telomeres prevent gene loss and protect chromosome integrity.

Human Chromosome Count

• Humans have 23 pairs (46 total) of chromosomes.

Homologous Chromosomes

• Pairs of chromosomes (one from each parent) that carry genes for the same traits.

Autosomes vs. Sex Chromosomes

• Autosome pairs (1-22) are identical, while sex chromosomes (23rd pair) differ between genders (XX or XY).

Purpose of New Cell Formation

• New cells are produced for growth, replacement of damaged cells, and reproduction in unicellular organisms.

Asexual Reproduction Types

• Mitosis occurs in eukaryotes, while binary fission occurs in prokaryotes.

Mitosis Definition

• Mitosis is the process of nuclear division.

Reasons for Cell Division

• Large cells experience DNA overload, increased difficulty in material exchange due to surface area-to-volume ratios, and decreased efficiency as they age.

Interphase Stages

• G1 Phase: Growth and synthesis of proteins/organelles.
• S Phase: DNA replication occurs.
• G2 Phase: Further growth and preparation for mitosis.

Centrioles and Spindle Fibers

• Spindle fibers, organized by centrioles, facilitate the separation of chromosomes during cell division.

Mitosis Acronyms

• Mitosis: PMAT
• Entire Cell Cycle: IPMATC

Mitosis in Eukaryotic Cells

• Not all eukaryotic cells undergo mitosis, e.g., nerve and muscle cells.

Prophase Details

• Longest phase of mitosis; chromatin condenses, centrioles align, and the nuclear envelope breaks down.

Metaphase Details

• Chromosomes line up along the cell's equator, connected to spindle fibers.

Anaphase Behavior

• Sister chromatids separate and move towards opposite centrioles.

Telophase Changes

• Chromosomes de-condense, nuclear envelopes re-form, and cytokinesis follows.

Cytokinesis in Different Cells

• Animal cells form cleavage furrow; plant cells form a cell plate for division.

Daughter Cells Post-Mitosis

• Daughter cells are identical to each other and to the parent cell, with matching chromosome counts.

Density-Dependent Regulation

• Cells halt division upon contact with others, which regulates growth and wound healing.

Anchorage Dependence

• Animal cells require attachment to divide, relying on extracellular matrix connections.

Cyclins Function

• Cyclins are proteins that regulate the timing of the cell cycle, present in high amounts during division.

Internal Regulators

• Proteins that ensure certain processes are completed before advancing the cell cycle.

Checkpoints Function

• Critical control points that determine if the cell cycle can proceed based on internal conditions.

G1 Checkpoint Outcomes

• A go-ahead signal leads to cell division; lack of signal results in entry into a non-dividing state (G0).

M Phase Checkpoint Purpose

• Ensures chromosomes are correctly attached to the spindle before anaphase to prevent chromosomal abnormalities.

External Regulators

• Proteins that respond to external cues to control the speed of the cell cycle.

Role of Growth Factors

• External regulators crucial for stimulating growth and division, especially during development and healing.

Cancer Definition

• A disorder characterized by uncontrollable division of certain cells.

Cancer Cell Behavior

• Cancer cells ignore growth regulation signals, leading to uncontrolled proliferation.

Tumors

• Masses formed by the uncontrolled growth of cancer cells.