Module 2: The Cell Cycle (M Phase and Definition of Terms)

The life span of a eukaryotic somatic cell

Cell Cycle

Any cell in the body excluding sex cells (sperm and egg)

Somatic cells

Three distinct phases of interphase

G1, S, and G2

Phase also known as growth/gap phase 1

G1 Phase

Cells that exit the cell cycle after G1 phase because they do not divide again

Muscle and nerve cells

What happens during G1 phase

Cell grows in size and synthesizes proteins and enzymes needed for S phase

Organelles that replicate during G1 phase

Mitochondria and Endoplasmic reticulum

Checkpoint at the end of G1 phase that checks if cell is fit to undergo DNA replication

G1 checkpoint

Reasons for failing G1 checkpoint

Insufficient size, lacking energy reserves, DNA damage

What happens if cell fails G1 checkpoint

Enter G0 phase or undergo apoptosis

State where cells exit the active cell cycle and stop dividing

G0 phase

Phase where copies of DNA are made

S phase

What is replicated during S phase

Entire genome of the cell

Cellular structures duplicated during S phase

Centrosome and spindle fibers

Proteins synthesized to package newly formed DNA into chromatin

Histone proteins

Duration of S phase

About 7 hours

What eukaryotic chromosomes are composed of

Chromatin

Composition of chromatin

DNA + histone proteins

Shortest and last phase of interphase

G2 phase

What happens during G2 phase

Cell continues to grow and produces enzymes/proteins necessary for Mitosis

Checkpoint that ensures DNA replication is complete and unchanged

G2 checkpoint

What happens if cell fails G2 checkpoint

Gene Repair or Apoptosis

Series of stages known as PMAT

Mitosis

Stage in cell cycle where nuclear division occurs

Mitosis

Structures made from microtubules that divide chromosomes

Mitotic Spindles

What produces mitotic spindles

Centrosomes

Longest phase of mitosis

Prophase

What happens during prophase

Chromatin condenses into chromosomes, nucleolus and nuclear membrane disappears

Division of metaphase into two parts

Prometaphase and Metaphase

What happens during prometaphase

Kinetochore is formed and nuclear membrane fully breaks down

Where spindle fibers attach during prometaphase

Kinetochore

What happens during metaphase

Sister chromatids align at the metaphase plate

Checkpoint present in metaphase

Spindle checkpoint

What happens during anaphase

Spindle fibers separate sister chromatids at centromere

What separated sister chromatids are called

Chromosomes

How chromosomes move during anaphase

Pulled to opposite poles by spindle fibers towards centrosomes

What happens during telophase

Nuclear membrane reforms around each set of chromosomes, chromosomes decondense into chromatin

What marks the end of mitosis

Telophase

Final step of M phase

Cytokinesis

What happens during cytokinesis

Division of the cytoplasm

How animal cells separate during cytokinesis

Cleavage furrow appears

How plant cells separate during cytokinesis

Cell plate forms

Two parts of M phase

Mitosis (nucleus divides) and Cytokinesis (cytoplasm divides)

What are genes?

Sequence of DNA

Structures within the cell that contains genes

Chromosome

One of two identical halves of a replicated chromosome

Chromatid

Entire structure that can be single chromatid or two sister chromatids joined by centromere

Chromosome

Organisms with clearly defined, membrane-bound nucleus

Eukaryotes

Number of chromosome pairs in human cells

23 pairs

Single-celled organisms that lack nucleus and membrane-bound organelles

Prokaryotes

Where DNA is located in prokaryotes

Nucleoid

Stage where chromosomes are highly condensed, organized, and aligned

Metaphase Chromosome

Parts of a metaphase chromosome

Centromere, Chromosome arms, secondary constriction, Satellite, Telomere

Part of chromatin where DNA is more condensed with little transcriptional activity

Heterochromatin

Part of chromatin where active genes are located, less condensed

Euchromatin

Site of chromosome where spindle fibers attach via kinetochore

Centromere

Highly complex multiprotein structure responsible for chromosome segregation

Kinetochore

Shortest arm of a chromosome

P arm

Longest arm of a chromosome

Q arm

Site of nucleolus formation

Secondary Constriction

Blot-like terminal part of chromosome extending beyond secondary constriction

Satellite

Tip of linear chromosome with many repeats of DNA sequence

Telomere

Phenomenon related to aging where telomeres shorten with cell division

Telomere Shortening

Telomere repeat sequence for humans

TTAGGG

Chromosomes found in oocytes of most animals (except mammals)

Lampbrush Chromosome

Chromosomes found in salivary glands of Drosophila larvae

Polytene Chromosome

Four types of chromosomes based on centromere position

Metacentric, Submetacentric, Acrocentric, Telocentric

Chromosome with centromere in median position and equal arm lengths

Metacentric

Chromosome with centromere in submedian position and unequal arm lengths

Submetacentric

Chromosome with centromere in subterminal position and highly unequal arm lengths

Acrocentric

Chromosome with centromere at the end

Telocentric