Chapter 2 Lecture

Prokaryotic cells

• Non nucleated

• relateively small

• Bactria and arhcea

• no Membrane bound orgenlles

• One long circular DNA molecule compacted into nucleoid area

Eukarotic cells

• Nucleated

• Relatively larger

• Includes plants, animals, fungi

• Membrane-bound organelles

How do prokaroytic cells replicate

Binary fission

• Seperartion of replicated circular chromosome

• Orgin of replication: location where DNA replication begins

• High rate

Viruses

• Neither prokaryotic nor eukaroytic

• outer protein coat surrounding nucleic acid (can have RNA or DNA genome)

• Not a living thing

Whats special about mitchodnria and chlorplasts

have thier own DNA

Telomeres

Repetitive sequences at the end of chromosomes that protect the interoir from degradtion

Sister chromatids

Exact copies of a chromosome; they only exist after DNA is duplicated and before divsion

Centreomere

Constricted region on chromosomes

• repetitive DNA

• location where the kinetochore assembles during division, attaching to spindle fibers.

P arm vs Q arm

P arm: petite (small arm)

Q arm: Loner

Why is the location of centromere important

dictates the apperance of chromosomes

Metacentric

centromre located in the middle

submetacentric

centromere location between middle and end

acrocentric

centromere location close to end

telocentric

centromere location at end

Homologous chromosomes

two of the same type of chromosome

• one version from mom, one verson from dad

Same type of chromosome with the same genes but they can have diffrent alleles

Sister chromatids

exact same copy of the chromosome

Haploid vs Diploid

Haploid refers to cells containing one set of chromosomes, while diploid cells contain two sets, one from each parent.

Cell cycle

Coninuous alternation between divsion and non division of cells

Composed of interphase and mitosis

interphase

initial stage of cell cycle, interval between divisions. Cells spend most of their time in interphase

Contains G₁ S and G₂ phases

G₀ phase

Stable, nondividing period of varible length

G₁ phase

Growth and developement of the cell

Phase of metabolic acitvity, cell growth and differentiation

S phase

Synthesis of DNA

Having commited to dividing, the cell synthesizes a second copy of its genome

G₂ Phase

prepartion for division, the cell has doubled in size

6 phases of M phase

Prophase

Prometaphase

Metaphase

Anaphase

Telophase

Cytokinesis

Prophase

Chromosomes condense and mitotic spindle forms

Prometaphase

Nuclear envelopme disintegrades, and spindle microtubules anchor to kinetochores

Metaphase

Chromosomes align on the metaphase plate; spindle-assembly checkpoint.

Anaphase

Sister chromatids seperate, becoming indiivual chromosomes that migrate toward spindle poles

Telophase

Chromosomes arrive at spindle poles, the nuclear envelope re-forms. and the condensed chromosomes relax

Cytokinesis

Cytoplasm Divides; cell wall forms in plant cells

G₁/S Checkpoint

the cell commites to dividing

• needs to have enough nutrients

• needs to have no major Dna damage

• and must have sufficient growth signals and hormones

G₂/M checkpoint

the cells check the integrity of the new and old DNA, it cannot move past this checkpoint with DNA damage

M checkpoint

during metaphase the cell checks to make sure the spindle fibers are attached properly

Genetic Consequences of the Cell Cycle

• Cycle produces two cells that are genetically identical to each other and to the cell that gave rise to them

• Newly formed cells contain a full complement of chromosomes

• Each newly formed cell contains approximately half the cytoplasm and organelle content of the original parental cell.

When does the number of DNA molecules in cells duplicate

during S

When does number of chromosomes per cell duplicate and half?

Duplicate during Anaphase

Half again during telophase and cytokinesis

Karyokinesis

Genetic material evenly diveded into two daughter cells during nucleaur division

Cytokinesis

Follows karyokinesis, partitions celular volume into two parts and encloses each cell with a plasma membrane

Cell plate vs cleave furrow

Cell plate: forms in plants, new cell wall

Cleavage furrow: forms in animals

Steps for mitosis

Prophase

Prometaphase

Metaphase

Anaphase

Telophase

Prophase

Chromosomes condense

Centrioles divide and move to opposite ends of cells

Nuclear envelope breaks down

nucleolus disintegrates

Chromatin fibers condense and become visible chromosomes and spindle fibers begin to form.

Prometaphase

period of chromosome movement

The nuclear membrane disintegrates

Spindle microtubules attach to chromatids

Metaphase

Chromosome configuration following mirgration

Chrmosomes line up on the metaphase plate

cohesion

protein complex that holds sister chromatids together

• complex formed during S phase

Anaphase

Centromeres split and sister chromatids seperate from each other; they are no longer chromatids but daughter chromosomes

when does complete disjunction occur

cohesin complex is cleaved by separase

Sister chromatids are pulled towards opposite poles of celsl

Telophase

Final stage of mitosis with two complete sets of chromosomes, one set at each pole

• chromosomes uncoil and become chromatin again

• nuclear envelope reforms

• spindle fibers disappear and nucleous reforms

• cytokinesis divides cytplasms

• cell enters interphase

Karyokinesis vs Cytokinesis

karyokinesis: Nucleus

Cytokinesis: cell

Role of cohesion

keeps sister chromatin together

what does mitosis make

2 diploid daughter cells indentical to the diploid parent cell

Meiosis

Critical to successful sexual reproduction of diploid organisms

• produced haploid gametes in animals

• produces haploid spores in plants that turn into gametes

Reduced amount of genetic material by half.

• most eukaryotes are diploid (2n) so most gametes and spores are haploid (n)

  • Human sperm and eggs have 23 chromosomes

  • Human zygotes and somatic cells have 46 chromosomes, 23 pairs

    • Fertilization restores diploid number

diploid

eukaryotes generally have 2 of each chromosome, one maternal and one paternal

• these are homologous chromosomes

Meiosis I vs Meiosis II

Meiosis I: Homologous chromosomes seperate

Meiosis II: Sister chromatids seperate

Genetic variation through meiosis

Crossing over of homologous chromosomes

• results in genetic exchange

• create intact chromosomes - mosaics of maternal and paternal homologs

Independent (random) assortment of chromsomes

• chromosomes line up randomly in meiosis

• a human gamete could have either maternal or paternal chromosomes, leading to many possible genetic combinations. (18 and 5, 11 and 12 etc.)

Prophase I

Chromosomes condense, homologous chromosomes synapse, corssing over takes place, nuclear envelope breaks down, mitotic spindle forms

Chiasmata

region where chromatids are still interwound

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

Bivalent and tetrades

form during synapsis in prophase I

Bivalent: two homologous chromosomes

Tetrad: two pairs of sister chromatids

Metaphase I

Homologous pairs of chromosomes line up on the metaphase plate

Homologous pairs of choromosomes line up along the metaphase plate

• tetrrads bind to spindle fibers and moves chromatids to metaphase plate

Chromosomes are at maximum shortness and thickness

Cohesin, separase, and shugoshin in Mitosis vs Meiosis

During metaphase of meisosis:

• Cohesion is degraded by enzyme separase

• Sister chromatid arms disjoin except at centromere

• The enzyme shugoshin prevents degradation of cohensin and centromere

Anaphase I

Homologous chromosomes seperate and move towards opposite poles

Disjunction: Homolgous chromosomes seperate

Half of each tetrad is randomly pulled to opposite poles

Mitosis vs Meiosis Anaphase

Mitosis anaphase: SC seperate

Meiosis anaphase I: HC seperate

Meiosis Anaphase II: Sister chromatids seperate

Telophase I

Chromosomes arrive at the spindle poles and the cytoplasm divides

reapperance of nuclear membrane

Meiosis II

Basically mitosis, sister chromatids are seperated

Prophase II

Chromosomes recondoense

Metaphase II

Inidivual chromosomes line up on the metaphase plate

Anaphase II

Centromeres divide ; sister chromatids are pulled apart to opposite poles.

Telophase II

One member of each homologous chromosome is at each pole

Chromosomes arrive at the spindle poles; the spindle breaks down and a nuclear envelope reforms

Cytokinesis in Meiosis II

Cytoplasm divides

What generates gamete variation and when

• crossing over during prophase I

• Independent assortment during metaphase I

What does meiosis make

4 haploid daughter cells that are not identical o the diploid parent cell

Spermatogenesis vs oogenesis

Spermatogenesis: takes place in the testes and produces 4 sperm

Oogenesis: takes place in the ovaries, produces one egg

Spores Vs. Gametes

Spores are produced by mitosis in the asexual cycle and produced by meiosis in the sexual cycle

Spores grow into a new organism on their own through asexual reproduction. Gametes (such as sperm and egg cells) must fuse with another gamete during sexual reproduction to form a zygote before any new growth can start

Are fungi haploid or diploid

Haploid

Sporophyte and gametophyte

Sporphyte: 2n, the diploid phase of the life cycle that produces spores through meiosis. what you can see

Gametophyte: n, the haploid phase that produces gametes by mitosis. usually hidden

what are polar bodies

get discarded