D2.1 Cell and Nuclear Division

Cell division

The process where a parent cell divides to produce two daughter cells

Binary fission

A simple division process in prokaryotes where one cell splits into two genetically identical cells

Mitosis

Nuclear division in eukaryotic cells that produces two genetically identical daughter nuclei with the same chromosome number

Meiosis

A two step division process that halves chromosome numbers and produces four genetically unique haploid cells for sexual reproduction

Cytokinesis

The physical division of a cell's cytoplasm to form two separate daughter cells

Actin

A structural protein fiber involved in cell movement and muscle contraction

Myosin

A motor protein that pulls actin filaments to generate movement

Cleavage furrow

A groove formed in an animal cell membrane as it pinches inward during cell division

Animal cell cytokinesis

Actin and myosin form a contractile ring beneath the plasma membrane that pinches the cell inward until it separates into two daughter cells

Plant cell cytokinesis

Vesicles containing cell wall materials assemble and fuse together in the middle of the cell

Cell plate

A temporary structure formed by plant cell vesicles that develops into a new dividing cell wall

Equal cytokinesis

The usual division of cytoplasm that distributes cellular contents equally between daughter cells

Mitochondria distribution

Each daughter cell must receive at least one mitochondrion to produce ATP through aerobic respiration

Mitochondrion

An organelle that produces ATP energy through aerobic respiration

Peroxisomes

Small organelles containing enzymes that break down toxic waste materials

Organelle distribution

Both daughter cells must receive organelles produced by the division of pre existing structures

Unequal cytokinesis

A division process where cytoplasm is split unevenly, producing daughter cells of different sizes

Oogenesis

The biological process in female ovaries that produces mature egg cells called ova

Primary oocyte

The original egg cell that undergoes meiosis during oogenesis

Secondary oocyte

The cell that receives almost all the cytoplasm, organelles, and energy stores during oogenesis

Polar bodies

Small nonfunctional haploid cells that receive very little cytoplasm during egg production and eventually disintegrate

Budding in yeast

A form of asexual reproduction where a smaller new cell grows directly out of the parent cell

Yeast bud formation

An outgrowth develops on the parent cell and receives less than half of its cytoplasm and organelles

Budding scar

A mark left on the parent yeast cell surface where a daughter cell detached

Diploid (2n)

Having two complete sets of chromosomes, one inherited from each parent

Role of mitosis

Maintains chromosome number and produces two genetically identical diploid daughter nuclei

Mitosis in growth

Produces new cells to increase tissue size

Mitosis in cell replacement

Replaces old or damaged cells with genetically identical cells

Mitosis in tissue repair

Produces new cells to repair damaged tissues

Asexual reproduction

Reproduction involving one parent that produces genetically identical offspring without gametes

Role of meiosis

Halves the chromosome number from diploid to haploid and produces four genetically unique daughter nuclei

Haploid (n)

Having one complete set of chromosomes

Meiosis in reproduction

Produces haploid gametes required for sexual reproduction

DNA replication

The process of copying DNA during interphase before nuclear division begins

Interphase

The stage before nuclear division when the cell grows and replicates its DNA

Sister chromatids

Two identical copies of a replicated chromosome joined together

Centromere

The central region of a chromosome where sister chromatids are held together

Histone proteins

Positively charged spool like proteins around which DNA wraps for organization

Nucleosomes

Basic structural units of eukaryotic DNA consisting of DNA wrapped around eight histone proteins

Chromatin condensation

The process where chromatin tightly coils into visible chromosomes at the beginning of cell division

Spindle apparatus

A network of microtubule fibers that moves chromosomes apart during cell division

Microtubules

Protein fibers that form the spindle apparatus and help move chromosomes during cell division

Microtubule motor proteins

Molecular engines that use ATP energy to move chromosomes along microtubule tracks

Cell poles

Opposite ends of a dividing cell toward which chromosomes move

Prophase

The stage when chromosomes condense, the nuclear envelope breaks down, and spindle fibers form

Chromosome condensation in prophase

Chromatin coils tightly to form visible chromosomes

Nuclear envelope breakdown

The nuclear membrane breaks down during prophase to allow chromosome movement

Microtubule Organising Centres (MTOCs)

Structures inside the cell that build and arrange microtubule fibers

Centrosomes

Microtubule organising centres in animal cells that contain centrioles and organize spindle fibers

Metaphase

The stage when chromosomes line up along the middle of the cell

Metaphase plate

The imaginary central plane across the middle of a dividing cell where chromosomes line up

Spindle attachment

Spindle fibers attach to centromeres to position and move chromosomes

Anaphase

The stage when sister chromatids separate and move toward opposite cell poles

Centromere splitting

The separation of sister chromatids during anaphase

Spindle fiber shortening

The process that pulls separated sister chromatids toward opposite cell poles

Telophase

The final stage of mitosis when chromosomes decondense and new nuclear membranes form

Chromosome decondensation

The process where tightly coiled chromosomes unwind back into chromatin

Nuclear membrane reformation

The formation of new nuclear membranes around each group of chromosomes during telophase

Spindle disintegration

The breakdown of spindle fibers during telophase

Cell elongation

The lengthening of the cell during the later stages of mitosis

Order of mitosis

Prophase, metaphase, anaphase, telophase

Interphase identification

Chromosomes are not visibly condensed and the nucleus remains intact

Prophase identification

Visible condensed chromosomes appear and the nuclear envelope breaks down

Metaphase identification

Chromosomes line up across the center of the cell

Anaphase identification

Sister chromatids separate and move toward opposite poles

Telophase identification

Two groups of chromosomes reach opposite poles and new nuclear membranes form

Reduction division

A type of cell division that reduces the chromosome number from diploid (2n) to haploid (n)

Purpose of chromosome reduction

Ensures the correct diploid chromosome number is restored after fertilization

Fertilization

The fusion of a haploid sperm and haploid egg to produce a diploid zygote

Zygote

A diploid cell formed when a sperm fertilizes an egg

Meiosis I

The first meiotic division that separates homologous chromosome pairs

Meiosis II

The second meiotic division that separates sister chromatids

Homologous chromosomes

A pair of chromosomes containing the same genes at corresponding locations, with one inherited from each parent

Prophase I

Chromosomes condense, homologous chromosomes pair up, and crossing over occurs

Bivalents

Pairs of connected homologous chromosomes formed during prophase I

Tetrads

Structures consisting of four chromatids formed when homologous chromosomes pair together

Crossing over

The exchange of equivalent DNA segments between non sister chromatids of homologous chromosomes

Non sister chromatids

Chromatids belonging to different homologous chromosomes

Metaphase I

Homologous chromosome pairs line up randomly along the middle of the cell

Chromosome separation in meiosis I

Homologous chromosomes move toward opposite poles while sister chromatids remain joined

Telophase I

Chromosomes reach opposite poles, nuclear membranes may reform, and cytokinesis produces two haploid daughter cells

Result of meiosis I

Two haploid cells containing chromosomes that still consist of two joined sister chromatids

Prophase II

Chromatin condenses again and new spindle fibers form in both haploid cells

Metaphase II

Sister chromatids line up along the center of each haploid cell

Anaphase II

Centromeres split and sister chromatids separate into individual chromosomes that move toward opposite poles

Telophase II

Chromosomes decondense, nuclear envelopes reform, and cytokinesis occurs

Result of meiosis II

Four genetically unique haploid daughter cells are produced

Nondisjunction

An error during meiosis where chromosomes or chromatids fail to separate correctly

Nondisjunction in anaphase I

Homologous chromosome pairs fail to separate and move to opposite poles

Nondisjunction in anaphase II

Sister chromatids fail to separate and move to opposite poles

Risk factor for nondisjunction

Increased maternal age

Nondisjunction consequences

Gametes receive either one extra chromosome (n + 1) or one missing chromosome (n minus 1)

Trisomy

A genetic condition where a cell has three copies of a chromosome instead of two

Cause of trisomy

Fertilization involving a gamete with an extra chromosome produces a zygote with three copies of that chromosome

Down syndrome

A genetic condition caused by an extra copy of chromosome 21

Down syndrome symptoms

Intellectual disabilities, heart defects, low muscle tone, and delayed development

Monosomy

A genetic condition where a cell has only one copy of a chromosome instead of two

Cause of monosomy

Fertilization involving a gamete missing a chromosome produces a zygote with only one copy of that chromosome

Turner syndrome

A chromosomal disorder in females caused by inheriting only one X chromosome, known as Monosomy X

Turner syndrome symptoms

Short stature, infertility, and heart defects