Biology 101 Exam 2

Mitosis

The division of a cell into two daughter cells that are genetically identical to the parent cell

• eukaryotic cell division

• division of nucleus

• production of somatic cells

Meiosis

A type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells

• eukaryotic cell division

• production of gametes

Binary Fission

Main type of cell division in prokaryotes

• how mitochondria and chloroplasts divide

• Copy DNA

• Separate DNA

Cytokenesis

Division of cytosol and other organelles after segregation of the genetic material into two daughter cells.

Functions of Mitosis

• Growth

• Repair/Replacement

• Asexual Reproduction

Asexual Reproduction

Reproductive process where egg and sperm aren’t needed

Chromosome

Structure carrying genetic material (genes and non-coding DNA) found in nucleus

Karyotype

an individual's complete set of chromosomes. Also refers to a lab-produced image of a person's chromosomes arranged in numerical order

Diploid (2n)

Cells/organisms with paired chromosomes

• 1 chromosome from each parent

Haploid (1n, n)

Cells/organisms with unpaired chromosomes

Centromere

The region of the chromosome to which the spindle fiber is attached during cell division

• where sister chromatids attach

Kinetochore

Protein structure (that forms on a chromatin during cell division) where microtubules attach during mitosis

Sister Chromatids

The identical copies formed by the DNA replication of a chromosome, with both copies joined together by a common centromere

Cohesins

Chromosome-associated protein complex that is critical for chromosome separation during cell division.

• connects sister chromatids

Cell Cycle

Life cycle of a cell, a series of events that takes place in a cell as it grows and divides

• G1 - S - G2 - M

G1 Stage

Cell cycle stage that consists of:

• Cell growth

• Transcription/Translation

• Duplication of organelles

• Preparation for DNA replication

S stage (Synthesis)

Cell cycle stage where DNA replication occurs

G2 Stage

Cell cycle stage that consists of:

• More growth

• Transcription/Translation

• Prepare to divide:

  • Centrosomes appear

M stage (Mitotic)

Cell cycle stage when the cell divides its copied DNA and cytoplasm to make two new cells.

• two distinct division-related processes: mitosis and cytokinesis.

Fate of organelles

• Endomembrane system

  • fragments into vesicle structures

  • reforms in daughter cells

• Mitochondria

  • split between two daughter cells

  • divide by binary fission to reproduce in new cell

Contractile Ring

A ring of actin filaments located below the cell membrane which constricts the middle of a dividing cell

Gametes

a reproductive cell of an animal or plant

Somatic Cells

the cells in the body other than sperm and egg cells

Zygote

Diploid cell resulting from the fusion of two haploid gametes; fertilized egg

Condense

What chromosomes do at the start of mitosis

Replicate

What chromosomes do prior to mitosis

Mitotic Spindle Microtubulues

During mitosis, they form a macromolecular structure known as the mitotic spindle that is responsible for the accurate segregation of chromosomes between the two daughter cells

Homologous Chromosomes

Pairs of chromosomes in a diploid organism that have similar genes, although not necessarily identical

Sex Chromosome

A type of chromosome involved in sex determination. Humans and most other mammals have two sex chromosomes, X and Y, that in combination determine the sex of an individual.

Autosome

Any chromosome that is not a sex chromosome

Alleles

Alternate forms of a gene ; found at the same place on a chromosome

Fertilization

The joining of an egg cell and a sperm cell

Centrosomes

Where microtubules grow from

• Microtubule Organization Center (MTOC)

Mitotic Spindle

A structure made up of microtubules that forms during cell division and separates duplicated chromosomes and moves them from the parent cell into the daughter cells

XX

Sex chromosomes that indicate a female

XY

Sex chromosomes that indicate a male

Daughter Cells

The cells that are formed after cell division

• In Mitosis: 2 diploid cells that are identical to each other and the parent

• In Meiosis: 4 haploid cells that are not identical to each other or the parent

Sexual Life Cycle

• Gamete formation (meiosis)

• Fertilization

• Growth (mitosis) & development

Stages of Meiosis

• Prophase I

• Metaphase I

• Anaphase I

• Telophase I

• Cytokinesis

• Prophase II

• Metaphase II

• Anaphase II

• Telophase II

• Cytokinesis

Prophase I (Meiosis)

• Chromosomes condense

• Nuclear envelope fragments

• Centrosomes migrate

• Meiotic spindle forms

• Synapsis occurs

• Crossing over occurs

Synapsis

Pairing of homologous chromosomes that happens during Prophase I of Meiosis

Crossing Over

Exchange of genetic material between non-sister chromatids that occurs during Prophase I of Meiosis

Synaptonemal Complex

Protein lattice between homologous chromosomes

Recombinant Chromatids

Two of the four chromatids present early in meiosis (prophase I) are paired with each other and able to interact

• new combination of alleles

Non-Recombinant Chromatids

There is no genetic recombination; It is more akin to the original or parent DNA.

Metaphase I (Meiosis)

• Homologous Pairs align on the metaphase plate

• random assignment/independent assortment

Independent Assortment

A genetic principle that states that the alleles of two genes will segregate into daughter cells independent of one another. That means that the allele a cell receives for one gene is not influenced by an allele it receives for another gene.

• Occurs in meiosis

• NOT in mitosis

Anaphase I (Meiosis)

• Kinetochore MTs shorten

• Synaptonemal Complex degrades

• Homologous chromosomes separate and move to the opposite poles of the cell

• Sister chromatids stay attached

• Non-kinetochore MTs lengthen and cell elongates

Telophase I/Cytokinesis (Meiosis)

• Each half of cell has complete 1n set of replicated chromosomes

• Each chromosome consists of 2 sister chromatids

• Interkinesis (intermission)

• NO DNA REPLICATION

Prophase II (Meiosis)

• Same at Mitosis

• Chromosomes condense

Metaphase II (Meiosis)

• Chromosomes aligned on metaphase plate

Anaphase II (Meiosis)

• Sister chromatids separated and moved to opposite poles of cell

Telophase II/Cytokinesis (Meiosis)

• Chromosomes decondense

• Nuclei reform

n=3

Haploid with three chromosomes

Genetic Variation in Offspring

Due to:

1. Mutation

2. Random assignment of chromosomes on metaphase I plate

3. Crossing over (>8.4m gametes)

4. Fertilization (random egg & sperm)

Disjunction

Disjoining DNA or chromosomes; the normal separation or moving apart of chromosomes toward opposite poles of the cell during cell division

Nondisjunction

Disjunction doesn’t work; homologous or sister chromatids don’t separate from each other

Aneuploid

The occurrence of one or more extra or missing chromosomes in a cell or organism

Trisomy

occurs when you have an extra copy of a chromosome

Monosomy

Occurs when you are missing a copy of a chromosome

Stages of Mitosis

• Prophase

• Metaphase

• Anaphase

• Telophase/Cytokinesis

Prophase (Mitosis)

• Chromosomes condense and become metaphase chromosomes

• Nuclear envelope degrades and disappears

• Mitotic spindle forms

Kinetochore Microtubules

Attached to kinetochores; connect chromosomes to microtubules of the mitotic and meiotic spindles in order to distribute the replicated genome from a mother cell to its daughters.

Non-Kinetochore Microtubules

Don’t attach to kinetochore; the aspect of the mitotic spindle that does not interact with chromosomes

Metaphase (Mitosis)

• Chromosomes line up on the metaphase plate

• Twice as many sister chromatids as chromosomes

Anaphase (Mitosis)

• Separation of DNA

• Cohesions degrade

• Kinetochore Mts get shorter

• Separate sister chromatins from each other and move them to opposite poles of the cell

• Non-kinetochore MTs lengthen - elongates the cell

Telophase/Cytokinesis (Mitosis)

• Opposite of prophase

• Chromosomes de-condense

• Nuclear envelope reassembles

• Mitotic spindle disassembles

• Microfilaments shorten

Checkpoints

Regulatory molecules at each cell cycle checkpoint “decide” if division should proceed

• problems here = could become cancerous

G1 Checkpoint

• Is growth factor present?

• Is cell big enough?

• Is DNA undamaged?

G2 Checkpoint

Is DNA replication complete?

Metaphase (M) Checkpoint

Are chromosomes attached to kinetochore microtubules?

Growth Factor

Stimulate cells to divide

• each has a specific receptor

• cells start & stop reproducing at the right time

Apoptosis

Occurs when a problem in cell division is not fixed; A type of cell death in which a series of molecular steps in a cell lead to its death

Tumor

Group of proliferating cancer cells that forms when a problem in cell division is not fixed but goes past the checkpoint anyway

• cells can be immortal

Signal Transduction

The mechanism by which a cell leads an external signal through a cell, transforming it biochemically into a series of discrete entities (internal response) with specific biochemical properties.

1. Reception

2. Transduction

3. Response

Reception

Stage in signal transduction when a cell detects a signaling molecule from the outside of the cell.

Transduction

Stage in signal transduction where receptors are activated in succession, relying molecules in signal transduction pathway

Response

Stage in signal transduction when activation of cellular response occurs

Anchorage Dependence

Cells have to connect to the right thing to divide

Contact Inhibition

The concept that crowded cells stop dividing

Stages of Cancer Cells

1. A tumor grows from a single cancer cell

2. Cancer cells invade neighboring tissue

3. Cancer cells spread to other parts of the body

4. Cancer cells may survive and establish a new tumor in the body

Benign

Non-cancerous tumor

Malignant

Cancerous tumor

Metastasis

The spread of cancer cells from the place where they first formed to another part of the body

Properties of Cancer Cells

• Cells divide with no growth factor

• Cells ignore contact inhibition

• Cells ignore anchorage dependence

Proto-oncogenes

Genes that encode signals, receptors, signaling molecules, and control proteins

• normal

Oncogenes

Cancer-causing genes

• always active

• tells cell to divide when they aren’t supposed to

Point Mutation

A genetic alteration caused by the substitution of a single nucleotide for another nucleotide

• leads to hyperactive or degradation-resistant protein

Gene Amplification

Multiple copies of the gene made, leads to normal growth-stimulating protein in excess

Translocation

Gene moved to a new locus, under new controls, leads to normal growth-stimulating protein in excess

Tumor Suppressor Proteins

Shut down cell division if conditions are not favorable

• if mutated:

  • cell cycle checkpoints ignored

  • damage cells proliferate

BRCA 1 and BRCA2

Work in concert to protect the genome from double-strand DNA damage during DNA replication

• Recognize DNA damage

• Recruit repair enzymes

BRCA Mutation

• Damaged DNA still goes through Mitosis

• Increased risk for breast & ovarian cancer

p53

Tumor-supressor protein that is activated whenever DNA damage or cell cycle abnormalities occurs

• Cycle cycle arrest, DNA repair, and cell cycle re-start

OR

• Apoptosis

p53 Mutation

• Damaged DNA/cells go through mitosis

• Risk of colon, breast, lung, and other cancers

Apoptosis

The process of programmed cell death. It is used during early development to eliminate unwanted cells

Hyper-methylation

Too much methylation, leads to gene being turned OFF (epigenetic phenomenon)

Telomerase

Maintains telomere length; chromosomes don’t shorten

• over-expressed = immortal cells

• activity detected in tumors

HeLa Cells

Immortal cell line commonly used in biological research; have active telomerase

Traditional Chemotherapy

Injection of chemicals into bloodstream to kill dividing cells

• non-selective