Cell Cycle

Cell Cycle

2 distinct phases

  • Interphase—prepares the cell for mitosis (division)

  • Cells spend the majority of the cell cycle in interphase

    • By the end of interphase, a cell has two full sets of DNA(chromosomes) and is large enough to begin the division process.

    • There are checkpoints happening before starting mitosis to prevent a cancer cell from spreading.

    • Stages of Interphase

      • G1—Cell grows and replicates organelles.

      • G0—The cell goes into a state in which it will never divide.

        • Neurological cells

        • Cardiac cells

      • S—DNA Synthesis (duplicates DNA)

        • 23 pairs of chromosomes, 46 in total

        • 46 pairs of chromosomes at one point to replicate the cell

        • Duplicates a microtubule—organizing structure called the centrosome, the centrosomes help separate DNA during the M phase

      • G2—Additional growth, excessive and detailed expansion (in order to hold replicated organelles)

  • Mitosis—the act of cell division; mitosis results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus.

  • Each cell has its own organelles, DNA, etc etc

  • The Chromosome strands break from two to four strands (two per chromatid)

    • Cytokinesis—the cytoplasmic division of a cell at the end of mitosis or meiosis bringing about the separation into two daughter cells.

    • Phases of Mitosis (PMAT)

      • Prophase

  1. Chromosomes condense, becoming visible

  2. Nuclear membrane disappears--The membrane protects the DNA (in the nucleus) You need to move the chromosomes, therefore the need for the removal of the membrane

  3. Centrioles separate by residing on opposite poles of the cell.

  4. Spindle fibers form and radiate toward the center of the cell (spindle fibers created in prophase)

    • Metaphase

  5. Chromosomes line up across the middle of the cell

  6. Spindle fibers connect the centromeres of each chromosome to the poles of the cell

    • Anaphase

  7. The Centromeres that join the sister chromatids split, taking the chromatids apart

  8. The Sister chromatids separate and biome individual chromosomes

  9. Separated chromatids will then move to the opposite poles of the cell

    • Telophase

  10. Chromosomes (each consisting of a single chromatid) uncoil.

  11. A nuclear envelope forms around the chromosomes at each pole of the cell

  12. Spindle fibers break down and dissolve.

  13. Cytokinesis begins

  • Cytokinesis

    • Division of the cytoplasm into two individual cells.

    • Process is different between plant and animal cells.

    • In animal cells, the cell membrane forms a cleavage furrow that eventually pinches the cell into two nearly equal parts, each containing its own nucleus and cytoplasmic organelles.

    • Plant cell cytokinesis

      • In animal cells, the membrane pinches closed.

In plant cells, a cell plate forms

  • Diploid Cell—somatic cells

    • A somatic cell-body cells or any non-sex cell

    • A cell that contains 2 sets of chromosomes

    • The number 2n where n represents the represented as 2n(n= the number of chromosomes

  • Haploid Cell—sex cells (half)

    • Sex cells—egg and sperm

    • Cells that have 1 copy of the chromosome

    • Contain 23 chromosomes

    • Haploid(sex cells) is 23, diploid(somatic cells) is 46

    • The number in a single set is represented as n.

    • So, n=23

    • Zygote- fertilized egg(reproduction has occurred)

  • Karyotype

    • Number and appearance of chromosomes

    • A karyotype allows you to see size, centromere, telomere, sex number and gender

    • The chromosomes are in homologous pairs because there are two parents

    • Pair 23 of the chromosomes assign the sex of person

    • XX→female

    • XY→male

  • Rate of cell division

    • The rate of cell division varies with the need for those types of cells. Some cells are unlikely to divide. (G0)

  • Chromosome Structure

    • Chromosomes condense at the beginning of mitosis by wrapping around a histone—Chromatin is DNA in its compact form.

    • Around 6.5 feet of DNA in a human cell

    • Telomeres protect condensed DNA.

    • A chromatid is one half of a duplicated chromosome.

    • Centromeres hold together sister chromatids in the middle.

  • Homologous pairs (same pair)

    • Homologous chromosomes are two chromosomes that are the same.

    • This happens because diploid organisms have two of each chromosome. Each of the pairs is a homologous pair.

    • One of the homologous pairs was inherited from the individual’s mother and the other one was inherited from the individual’s father.

    • For example, the two chromosomes #1 are homologous. However a chromosome #1 and a chromosome #2 are not homologous because they are different.

  • Asexual reproduction

    • These are genetically identical to the parent

    • No joining of gametes

Pros vs Cons

Pros

Cons

  • Cost is lower—energy used to reproduce is not as high as it is to reproduce sexually

  • All asexual organisms can reproduce

  • No need to attract a mate

  • Abiotic factors are not changing, things are stable

  • No genetic variation

  • Not stable in constantly changing environments

  • 4 types

    • Binary Fission

      • Happens in prokaryotic cells (bacteria)

      • 2 daughter cells genetically identical to the parent cell

      • Bacterial chromosomes are copied

      • Just like in mitosis, the chromosomes move away from each other

      • When the cell doubles in size it undergoes cytokinesis

      • End result: 2 new daughter cells

        • Example: Bacteria

    • Budding

      • Happens in Eukaryotic cells

      • Budding occurs when a small projection that grows on the surface of the parent organism that forms a new individual

        • Example: Hydra: aquatic species,

    • Fragmentation

      • Happens in Eukaryotic cells

      • Splits in two, each growing into individual organisms

        • Example: Sea star

    • Vegetative Reproduction

      • Happens in Eukaryotic cells

      • Modification of stem or underground structures of the parent organism

      • The “runners” branch out and offspring branch out, line plants with vines

        • Example: Strawberries, Watermelon

  • Sexual reproduction

    • Involves the joining of gametes together

    • Has a genetic mixture of both parents

  • Sexual and Asexual Reproduction

    • Some species can reproduce sexually and asexually such as a sea Anemone

    • Budding

    • Creates sperm and eggs

    • Broadcast spawning

    • Female releases eggs into water column, male releases sperm into water column after sensing the female

  • Cancer

    • Characterized by uncontrolled cell division

      • Divide more often than healthy cells

    • Arises when the cell cycle is disrupted

      • Result of failure in the checkpoints, damage to the cell/DNA: mutations, failure to carry out a phase

    • Divide when surrounded by neighboring cells, and in the absence of growth factors required for division

    • Divide much more than healthy cells

    • Cancer cells will build up on each other, signified by cancerous tumors that protrude

  • Two forms of Tumors

    • Benign Tumor

      • Remains clustered and can be removed

    • Malignant tumor

      • Malignant tumors metastasize (broken away and continuing to replicate in other parts of the body)

  • What does Cancer do?

    • Body cannot differentiate cancer cells

      • Continues to supply them with blood and nourishment

    • Cancer cells do not carry out necessary functions

    • Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation

  • Why is Cancer harmful?

    • Cancer cells do not perform specialized functions needed in specific areas

      • This means the body has large clamps of useless Cells that require food and blood supply

      • Stores large clumps of useless cells

    • If tumors grow too large, that can put pressure on the surrounding organs

    • If cancer cells are left unchecked, the organism will eventually die

  • Cancer cell origin

    • Come from normal cells that have suffered damage to genes that are involved in protein production for cell cycle regulation

      • Mutations

    • Most cancer cells have errors in one of two types of genes

    • Oncogenes—accelerate the cell cycle

    • Genes that contribute to the cell cycle checkpoints

  • CHECKPOINTS

    • G1 Checkpoint

      • Checks for:

        • Cell Size

        • Nutrients

        • Growth factors

        • DNA damage

      • This is important because after G1, it goes to G2 to replicate DNA

    • G2 Checkpoint

      • Checks for DNA Damage and DNA replication

        • Two options for defective cells:

          • Lysosomes institute apoptosis

          • Or enters G0

    • Spindle Checkpoint

      • Checks for the chromosome attachment at the metaphase plate

      • Cell scans itself, if a chromosome is outside the area, the cell will be paused. The spindle will then reel back the chromosome to continue

  • Cancer inheritance/Acquisition

    • Breast cancer be inherited from specific genes with error codes

      • Radiation or chemical exposure

    • UV Radiation-causes damage to the cell’s DNA

    • Air pollutants

    • Carcinogens, tobacco/air pollutants, promotes cancer in lungs

  • Treatment

    • Radiation—used to kill cancer cells and shrink tumors (for benign tumors

      • Damages a cell’s DNA so the cell cannot divide

    • Chemotherapy—uses drugs, often in combination, to kill actively dividing cells. Kills both cancerous and healthy cells, as does radiation. Chemotherapy is systemic as opposed to radiation (for malignant tumor

    • Surgery—cuts that 2