Unit 4

Describe the structure of chromosomes using terms such as chromatin, histones, sister chromatid, centromere.

Histones: proteins that package and condense DNA into chromosomes

Chromatin: the complex of DNA and proteins that makes up eukaryotic chromosomes

Sister Chromatids: two copies of a duplicated chromosome attached to each other by proteins at the centromere

Centromere: the region on each sister chromatid where it is most closely attached to its sister chromatid

List the three stages of interphase in order. What happens in each stage?

G₁ Phase: first growth phase of cell cycle before DNA replication begins. cells grows in size, synthesizes proteins, and duplicates organelles like mitochondria and ribosomes

S Phase: synthesizes phase. stage where DNA is replicated

G₂ Phase: second growth phase of cell cycle after DNA replication. checks replicated DNA for errors and continues cell growth and duplication of organelles in final preparation for mitosis.

What are the 5 stages of mitosis in order?

1. Prophase

2. Prometaphase

3. Metaphase

4. Anaphase

5. Telophase/Cytokinesis

What happens during the prophase stage of mitosis?

Chromatin fibers coil into visible chromosomes, each made of 2 sister chromatids. Mitotic spindle begins to form ( composed of centrosomes and microtubules), involved in the movement of chromosomes. Centrosomes migrate away from each other by lengthening of microtubules

What happens during the prometaphase of mitosis?

• chromosomes become more condensed.

• nuclear envelope fragments.

• chromosomes are now at opposite poles of the cell.

• microtubules extending from each centrosome begin to invade nuclear area.

• some microtubules attach to chromosomes

What happens during the metaphase stage of mitosis?

chromosomes line up equidistant between the two poles with centromeres of duplicated chromosomes running along metaphase plate

Metaphase Plate: an imaginary line located midway between the two poles of a cell during metaphase

What happens during the anaphase stage of mitosis?

• chromatids part from each other, becoming an independent chromosome.

• newly formed chromosomes move apart toward opposite ends of the cell as the microtubules they are attached to shorten.

• Cell elongates

What happens during the telophase stage of mitosis?

• each pole of the cell has full set of chromosomes

• two daughter nuclei form at opposite ends of the cell

• nuclear envelope forms, made of fragments of parent cell’s nuclear envelope and other parts of endomembrane system

• chromosomes begin to unravel, becoming less condensed

• microtubules of spindle apparatus break down

What is cytokinesis?

the division of the cytoplasm to form two separate daughter cells immediately after cell division

Describe the basics of the cell cycle control system.

Cell Control System: a cyclically operating set of molecules in the eukaryotic cell that both triggers and coordinates key events in the cell cycle

Cyclins: a cellular protein that plays an important role in regulating the cell cycle. acts as checkpoints in the cell cycle

• if there is not the right concentration of cyclins or other regulatory proteins at a given checkpoint, cell will not enter next phase of cell cycle

• cell may sometimes enter G₀ phase, or even cause cell to undergo apoptosis without right cyclins

Differentiate between benign and malignant tumors. What are the different treatment options for each?

Cancer: a disease caused by uncontrolled cell division

Tumor: an abnormal mass of tissue that formed due to unregulated cell division

Benign Tumor: a tumor that is isolated and generally harmless. does not interfere with normal organ function

• Treatment: can usually be removed with surgery

Malignant Tumor: a tumor that can invade nearby tissues and spread to other parts of the body

• Treatment: can usually be treated by radiation

Metastasis: the spread of cancer cells to locations distant from their original site

• Treatment: usually treated with chemotherapy (drugs administered to circulatory system that are toxic to dividing cells)

Contrast asexual and sexual reproduction.

Asexual Reproduction: method of reproduction which requires only one parent that contributes all of their DNA to their offspring without fusion of gametes

Sexual Reproduction: reproduction arising from fusion of two gametes

Gametes: a haploid reproductive cell such as an egg or sperm, that is formed by meiosis

Describe the different types and amounts of chromosomes found in somatic cells and gametes, respectively

• somatic cells that contain all 46 chromosomes are diploid

Diploid Cell: a cell containing two sets of chromosomes, one set inherited from each parent

Haploid Cell: a cell containing only one set of chromosomes (23)

What are the major differences between mitosis and meiosis?

Meiosis is the cell duplication process that produces gametes

• starts with diploid cell, ends with 4 unique haploid cells

two cell divisions that produce four daughter cells (Meiosis I and Meiosis II)

What are the three mechanisms that occur in meiosis that contribute to genetic variation in a population?

Crossing over: the reciprocal exchange of genetic material between non-sister chromatids during prophase I of meiosis. (shuffles specific genes across different homologous chromosomes)

• crossing over events can create recombinant chromosomes: a chromosome that contains portions of both the maternal + paternal chromosome

Independent Assortment: maternal and paternal homologous chromosomes are randomly aligned with one of the poles (shuffles which chromosomes end up in a haploid cell)

Random Fertilization: the process where a random sperm and random egg fuse due to chance

What happens in prophase I of meiosis?

• chromosomes condense

• nuclear envelope breaks down

• centrosomes separate

• spindle fibers form and attach to chromosomes

• homologous chromosomes pair up

• synapsis and crossing over occur

Synapsis: homologous chromosomes physically connect to each other along their lengths

What happens during metaphase I of meisosis?

• pairs of homologous chromosomes line up at the metaphase plate

• each chromosome is randomly aligned to one of the poles (independent assortment)

• both chromatids of one of the chromosome are attached to microtubules from the same spindle pole (different from mitosis)

What happens during anaphase I of meiosis?

• homologous chromosomes separate and move to opposite poles

• sister chromatids remain attached

• maternal X goes one direction, paternal X goes other direction

What happens during telophase I of meiosis?

• nuclear envelope forms around each set of chromosomes at each spindle pole

• cytokinesis separates the two daughter cells

• each daughter cell is now haploid and has one set of duplicated chromosomes

What happens during prophase II of meiosis?

• nuclear envelope breaks down

• chromosomes condense

• centrosomes migrate

• spindle apparatus forms

What happens during metaphase II of meiosis?

• chromosomes align at the metaphase plate

• microtubules from opposite poles attach to the centromeres of sister chromatids

because crossing over occurred, sister chromatids may not be genetically identical

What happens during anaphase II of meiosis?

• sister chromatids separate and move toward centrosomes at opposite spindle poles

• each chromatid is now individual chromosome

What happens during telophase II of meiosis?

• nuclei form around each haploid set of chromosomes

• chromosomes condense

• cytokinesis separates two daughter cells

one diploid cell —→ four haploid daughter cells

• each daughter cell is genetically unique from each other and the parent cell