Cell Division and Mitosis

These flashcards encapsulate key concepts related to cell division and mitosis covered in the lecture notes.

Prokaryotic Cell Division

Cell division in prokaryotes occurs as binary fission, where a single cell divides into two halves.

• genetic information (DNA) = singular + circular + double stranded

• begins at replication origin + continues bidirectionally

• pretty quick (~20 minutes)

Binary Fission

The process by which a prokaryotic cell divides into two daughter cells, each with a full copy of the genetic material.

• PROKARYOTES

• ori = start site

• ter = termination site

Eukaryotic Chromosomes

Genetic information in eukaryotic cells is stored in chromosomes, most commonly ranging from 10 to 50 in body cells.

• humans have 46 chromosomes (23 pairs) from mom + dad

Cell Cycle

The life cycle of a cell, divided into G1 (growth), S (synthesis), G2 (growth), M (mitosis), and C (cytokinesis).

1. cell growth + activity (DNA replication)

2. nuclear division (mitosis)

3. division of cytoplasm (cytokinesis)

Mitosis

A type of nuclear division where replicated DNA is divided equally between two daughter cells.

• exact genetic copies of parent cell

• 2n → 2n

• miotic cytoskeleton separates replicated DNA perfectly into daughter cells

Meiosis

A process of sexual reproduction that produces daughter nuclei with half the number of chromosomes as the parent.

• arrangement of genees are different from parent cell

• 2n → n

• egg/sperm

Chromosomes

Hereditary information within the nucleus is distributed among linear DNA molecules.

• DNA + proteins

Packing Linear DNA

DNA is packed into the nucleus after being shortened by histone proteins

• NUCLEUSOME: 8-protein nucleusome core particle forms when DNA winds around H2A + H2B + H3 + H4 (histones)

  • attracted by charges

• linker segments connects nucleusome

• nonhistone proteins associate with DNA + proteins (chromatin)

Solenoid Model

Predicts the nucleosomes spiral helically with about six nucleosomes per turn.

• look like beads on a string (10-nm chromatin fiber + compacts DNA by factor of ~7)

• model for 30-nm chromatin fiber: nucleosome + linker are bound by H1 (fifth histone protein)

Further Packing

• euchromatin = loosely packed

  • highly expressed regions

  • true/typical

• heterochromatin = dense packing

  • different

Sister Chromatids

The two identical copies of a chromosome, connected at the centromere, formed during DNA replication.

• held together by sister chromatid cohesion (protein complex)

• centromere = where sister chromatids are joined together

Chromosome Segregation

The equal distribution of chromosomes into each daughter nucleus during cell division.

Homologous Chromosomes vs. Sister Chromatids

• homologous chromosomes: pairs of chromosomes from parent

  • SIMILAR but not identical

  • different variations

  • from mom + dad

• sister chromatids: identical copies of single chromosomes

  • produced during DNA replication

  • IDENTICAL

Ploidy

The number of sets of chromosomes in a cell; haploid (n) for one copy, diploid (2n) for two copies.

• homologs = one copy of each chromosome → haploid (n)

• most eukaryotes = two copies of each chromosome → diploid (2n)

  • homologous chromosomes (from mom + dad)

Karyotype

An individual's complete set of chromosomes, used to study chromosomal abnormalities.

• diploid = two copies of each chromosome

  • body cells

  • made up of sister chromatids joined at centromere

  • mitosis

• haploid = single copy of each chromosome

  • sex cells

  • meiosis

Interphase

When the cell undergoes growth to ready itself for mitosis.

• G1 = growth + longest

  • makes proteins + molecules required in S phase

• S = DNA replication

  • each chromosome is copied + held together → sister chromatids

• G2 = growth

  • cell makes more proteins + other molecules for M phase

  • organelles replicate + microtubules organize

G0 Phase

Many cells in G1 stop dividing and are shunted at G0 phase.

• normal functions

• NOT growing + NO DNA replication

• CAN go into G1 if needed

3 Checkpoints

• cyclins + Cdks control checkpoints

  • cyclins = proteins that activate Cdks

  • Cdks = enzymes that are on/off by adding phosphate

  • cyclin amount VARIES + Cdks stay CONSTANT

1. G1/S = cell size + nutrients + DNA damage

2. G2/M = DNA replication check

3. mitotic spindle = check if chromosomes attached to spindle fibers + lined up

Animal Spindles

A structure made of microtubules that orchestrates the movement of chromosomes during mitosis.

• centrosome = main microtubule organizing center (MTOC)

  • contains centrioles → divided + duplicated

  • asters = microtubules extending from centrosomes

Prophase

The phase of mitosis after interphase.

• long DNA (coiled tight = short/thick shapes) condenses

• cell builds spindle apparatus + grows centrosomes @ opposite oples

  • asters = radial array of microtubules in animals

• TOWARDS END: nuclear envelope + nucleolus START to disappear

Prometaphase

The phase of mitosis after prophase when the nuclear envelope disassembles and spindle microtubules attach to kinetochores.

1. nuclear envelope breaks down

   1. chromosomes free in cell

2. open/closed mitosis

   1. open = envelope gone → might need more space?

   2. closed = envelope stays

3. kinetochores form

   1. handle for spindle fiber

   2. forms on each sister chromatid at centromere

4. spindle fiber

   1. OPPOSITE poles

   2. on kinetochores

5. nonkinetochores

   1. overlap

   2. help stabilize

Metaphase

The phase of mitosis where chromosomes are moved to the middle.

• spindle microtubules move chromosomes at spindle midpoint (metaphase plate)

• condensation → chromosomes have certain characteristic shape determined by length + location

• karyotype

Anaphase

The phase of mitosis where sister chromatids are pulled apart to opposite poles of the cell.

• removal of cohesin proteins from all chromosomes

• 2 forms of movement

  • anaphase a = motor proteins at spindle poles pull kinetochore to pole (shorten)

  • anaphase b = nonkinetochore elongate cell (lengthen)

    • motor proteins on nonkinetochores walk in opposite directions

Telophase

The final stage of mitosis where chromosomes decondense, nuclear envelopes reform, and nucleoli reappear.

• 1 BIG cell + 2 nuclei

1. chromosomes uncoil

   1. loose DNA (decondense)

2. spindle breaks

   1. no pulling fibers

3. new nuclear envelope

   1. made around 2 nuclei

4. nucleolus comes back

   1. restarts normal activity (RNA production)

Cytokinesis

The process that divides the cytoplasm of a parental cell into two daughter cells at the end of mitosis.

• furrow/contractile ring pinches cell until cytoplasm is cut in two

• cell plate forms + grows laterally until cytoplasm divides

• plane of cytoplasmic division determined by layer of microtubules at former spindle midpoint (metaphase plate)

Furrowing/Contractile Ring

• furrowing = resulting visible external surface indentation/groove

• contractile ring = intermolecular motor (actin/myosin) that constricts

Cell Plate

A structure forming during cytokinesis in plant cells, created by the fusion of vesicles, which eventually becomes the new cell wall.

• grows laterally