Chapter 2 - Mitosis and Meiosis

Prokaryotic cells:

• non-nucelated

• bacteria and archaea

Eukaryotic cells

• nucleated

• protists, plants, fungi, and animals

What is the difference in chromosomes between bacteria and eukaryotes?

Bacteria have 1 circular chromosome, eukaryotes have multiple linear chromosomes.

What is the end product of mitosis?

Mitosis leads to production of two identical daughter cells, each with the same number of chromosomes as parent cell.

What is the end product of meiosis?

Meiosis reduces genetic content and leads to production of sex gametes, which contains half the number of chromosomes.

What do prokaryotic organisms have that eukaryotic organisms possess?

• nuclear envelope

• membranous organelles

What is unique to prokaryotic cells?

• one long, circular DNA molecule (chromosome) compacted into nucleoid area

• Does not undergo extensive coiling like eukaryotic cells - DNA not as extensively associated with proteins

• Lack distinct nucleolus, but do contain genes for rRNA synthesis

Cytosol

colloidal material which surrounds cellular organelles

Cytoskeleton

made of microtubules and microfilaments, and provides lattice of support for structures within cell

What are the structures that the cytoskeleton is made of?

• Microtubules: made of protein tubulin

• Microfilaments: derived from protein actin

• Intermediate Filaments: made of other proteins (like kertain)

What are cilia and flagellum made of?

Tubulin

Smooth ER

site of lipid (fatty acid) synthesis

Rough ER

studded with ribosomes, site of membrane protein synthesis & modification

Ribosomes

site where genetic information in mRNA is translated to protein

Golgi Apparatus

modifies and packages proteins and lipids, especially proteins destined to be exported from the cell

Mitochondria

• found in most eukaryotic cells including animal and plant cells

  • site of oxidative phases of cell respiration and ATP synthesis

Chloroplasts

• found in plants, algae, and some protozoans

• site of photosynthesis

What is the Endosymbiotic Theory?

key organelles inside complex eukaryotic cells - specifically mitochondria and chloroplasts - originated independent as prokaryotic bacteria that were engulfed by a larger host cell

What is the support for Endosymbiotic Theory?

• both mitochondria and chloroplasts contain DNA distinct from that found in nucleus and ribosomes distinct from those in the cytoplasm

• mitochondria and chloroplast duplicate their DNA and divide in manner similar to bacteria

Centrosomes

• found in animal and plant cells

• centrosomes organize spindle fibers that function in meiosis and mitosis

Centrioles

• animal cell specific structures that are housed in the centrosomes

• help form cilia and flagella in addition to spindle fibers

Spindle fibers

• composed of microtubules consisting of polymers of protein tubulin

• play important role in movement of chromosomes as they separate during cell division

Centromere

• constricted region on chromosomes

• repetitive DNA (171 BP repeats in humans)

• location where the kinetochore assembles during division

Kinetochore

where the spindle fibers attach

Metacentric

centromere location in the middle

Submetacentric

centromere location between middle and end

Acrocentric

centromere location close to end

Telocentric

centromere location at end

Telomeres

repetitive sequences (TTAGGG in humans) at the ends of chromosomes that protect the interior from degradation

Sister chromatids

exact copies of a chromosome; they only exist after DNA is duplicated and before division

Centromere

constricted region on chromosomes (repetitive DNA, what the kinetocore forms around)

Homologous chromosomes

two of the same type of chromosome

Alleles

different versions of genes

Genes

the basic physical and functional unit of heredity, made up of a specific sequence of DNA (or RNA in some viruses) that provides instructions for making functional products like proteins or RNA molecules

Somatic cells

body cells

Diploid

two complete sets of chromosomes, with one set inherited from each biological parent

Haploid

a cell or organism has a single, complete set of unpaired chromosomes

Karyotypes

• used to analyze a cell’s chromosomes

  • used to diagnose genetic disorders

Are sex-determining chromosomes homologous?

no

p arm

the short end of a chromosome

q arm

the long end of a chromosome

Mitosis

• single-celled fungi, protists, and algae: mitosis serves as basis for asexual reproduction

• multicellular organisms: responsible for wound healing, cell replacement, and growth

• zygote: single-celled fertilized egg - mitosis drives its growth and development

Karyokinesis

genetic material evenly divided into two daughter cells during nuclear division (2 nuclei)

Cytokinesis

follows karyokinesis, partitions cellular volume into two parts and encloses each cell with a plasma membrane

Cell Plate

new cell wall that forms in plants

Cleavage furrow

shallow groove or indentation that forms on the surface of animal cells during cell division

Karyokinesis stages

• prophase

• prometaphase

• metaphase

• anaphase

• telophase

Prophase

• chromosomes condense

• centrioles (in animal cells only) divide and move to opposite ends of cell

• nuclear envelope breaks down

• nucleolus disintgerates

• chromatin fibers condense and become visible chromosomes

Prometaphase

period of chromosome movement

Metaphase

• chromosome configuration following migration

• chromosomes move to metaphase plate of cell

• spindle fibers bind to kinetochore (protein layers on the centromere) and move chromosomes

Sister chromatids

two parts of each chromosome: genetically identical - visibly connected at the centromere

Cohesin

protein complex that holds sister chromatids together until metaphase - complex formed during S phase

Anaphase

• centromeres split and sister chromatids separate from each other (disjunction); they are no longer chromatids but daughter chromosomes

Complete disjunction in anaphase

• occurs when cohesin complex is cleaved by separase

• sister chromatids are pulled toward opposite poles of cell

Telophase

• chromosomes uncoil and become chromatin again

• nuclear envelope reforms

• spindle fibers disappear and nucleolus reforms

• cytokinesis divides cytoplasm

• cell enters interphase

Cell Cycle

• continuous alternation between division and non-division of cells

• composed of interphase (divided into G1, S, and G2) and mitosis (M phase)

• non-dividing cells are said to be in G0

Interphase

• initial stage of cell cycle, interval between divisions

  • cells spend most of their time in interphase

S phase

• when DNA synthesis occurs

• phosphate is needed to synthesize nucleotides, so it is taken into the cell during S phase

• S phase is in between G1 and G2 phases

G1 phase

phase of metabolic activity, cell growth, and differentiation

G1/S checkpoint

the cell commits to dividing (non-dividing cells are in G0)

• needs to have enough nutrients to grow

• needs to have no major DNA damage

• in multicellular organisms, the cell cycle is also regulated by hormones and growth factors

S phase (cont.)

having committed to dividing, the cell synthesizes a second copy of its genome

G2 Phase

• the cell finishes preparations or division

• by the end of G2, the cell has doubled in size

G2/M checkpoint

the cells check the integrity of the new & old DNA - cannot move past this checkpoint with DNA damage

M phase

mitosis, the cell divides

M checkpoint

during metaphase, the cel checks to make sure the spindle fibers are attached properly (also called the spindle assembly checkpoint)

cancer

uncontrolled cell division that is a result of a disruption in regulation

Kinases

enzymes that phosphorylate metabolites and other proteins - changes the protein’s chemistry and can turn other proteins on and off

Cyclin dependent Kinases (CDKs)

• serve as “master control” molecules

  • they control cellular process by phosphorylating proteins, which can alter the proteins’s function (phosphorylation is an on/off switch for some proteins)

Cyclins

• proteins that bind with kinases, activating them at appropriate times during cell cycle

• different cyclins are produced at different phases of the cell cycle and act as the cell’s clock

Meiosis

• produces haploid gametes in animals

• produces haploid spores in plants that turn into gametes

What is the difference between Meiosis I and Meiosis II?

Meiosis I generates homologous chromosomes, and Meiosis II produces sister chromatids.

Meiosis gives rise to genetic variation in gametes through:

• crossing over of homologous chromosomes

• independent (random) assortment of chromosomes

Crossing over of homologous chromosomes

• results in genetic exchange between members of homologous pairs of chromosomes

• creates intact chromosomes - mosaics of maternal and paternal homologs

Independent (random) assortment of chromosomes

• chromosomes line up randomly in meiosis

• a human gamete could have 18 paternal chromosomes, 5 maternal chromosomes or 11 paternal chromosomes and 12 maternal chromosomes or any other combination

• metaphase at this stage is random! every gamete made is unique

Prophase I

• A diploid cell duplicates its genetic material prior to meiosis

• prophase I is like mitotic prophase, except homologous chromosomes pair up, this is called synpasis

• nuclear envelope and nucleolus break down, and two centromeres of tetrad attach to spindle fibers

• bivalents and tetrads form during synapsis

Chiasmata (singular chiasma)

• region where chromatids are still intertwined

• point where non-sister chromatids have undergone genetic exchange through crossing over