Biol 211 Final Exam

Dna Organization in Eukaryotes

muiltiple linear dsDNA molecues in a nucleus

Dna regulation and organization

double helix is condensed into chromatin

First step of Dna condensing

wrapped twiceish around histone proteins to form a nucleosome

repeating series of nuclosomes

10nm chromotin fibre

“normal” state of dna

chromatin

chromatin during DNA replication and translation

unwinds

cell division chromatin

condesnses further into chromosomes

nucleosome

histone octamer

30mn chromatin fibre

H1 binds linker DNA can coils nucleosomes to create.

DNA packing along chromosome

NON uniform

Euchromatin

regions of lower DNA compaction, genes are actively expressed

Heterochromatin

regions of high DNA compaction, gene expression is silenced

Constitutive Heterochromatin

DNA always highly compacted, centromeres and telomertic regions

Facultative Hetrochromatin

can switch to euchromatin depending on cell type and during cell development

Chromosome Organization

fully compact form of DNA, structure protects DNA from damage, can be separated easily and transmitted during cell division

essential components of eukaryotic chromosomes

Ori, Telomeres, Centromere

Origin of Replication (ori)

Multiple DNA sequences along chromosome that initiate DNA replication

Telomeres

DNA sequences located at the ENDs of chromosome that prevent degradation

Centromere

DNA sequences required for correct segregation of chromosomes during cell division

Pioldy of Eukaryotes

Diploid. two copies of each homologous chromosome

Pioldy of Sex Cells of Eukaryotes

haploid genome

some Eukaryotes Ploidy

Polyploid more than a pair of each chromosome

Dna organization in Prokaryotes

single circular dsDNA molecule

Prokaryote Dna compaction

use histone like proteins (HLP), also called nucleoid associated proteins (NAPs)

Plasmids

small independent circular DNA molecules in prokaryotes

Plasmid genes

carry non life essential genes, carry bonus genes that give advantages in some environments

Bonus genes give

antibiotic resistance, and virulence

Eukaryotic Cell cycle stages

G1, G0, S, G2, and M phase

Stages of Mitosis

Prophase, metaphase, anaphase, telophase

G1 stage

longest and most variable phase, cell is doing what it's supposed to do

G0 stage

Cell cycle resets, cell stops replicating

S stage

Interphase, DNA Replication Starts

G2 Stage

second gap, shorter and more regulated, Interphase ends

M phase

nucleus divides then cytokinesis

Homologous Chromosomes

parental pair of DNA molecules, number of genes on both are the same but the alleles might differ

DNa replication (S phase)

Each DNA molecule is replicated independently, after replication each Dna molecule exists as a pair of sister chromatids that are attached at the centromere.

Microtubules

Structural proteins change length to support cell structure movement and division.

Centrosome

a pair of centrioles which are composed of microtubules, organize microtubule formation

Prophase (mitosis)

The first stage of mitosis where DNA condenses into chromosomes, centriole pairs move apart, and the microtube spindles start to form.

Chromosome State in Prophase

Diploid (2n) condition consisting of 4 DNA molecules, with each chromosome containing 2 sister chromatids.

S Phase (Interphase)

The stage between G1 and G2 where DNA replication and centriole duplication occur.

Centriole behavior in Prophase

Duplicated(G2) centriole pairs begin to move apart to opposite poles of the cell to organize the mitotic spindle.

Spindle Formation

The assembly of microtubule spindles that begins during prophase to eventually separate sister chromatids.

Late Prophase

nuclear membrane breaks down

Prometaphase (Mitosis)

nuclear envelope is completely gone, centrosomes reach opposite poles, and microtubules attach to chromosomes.

Chromosome State in Prometaphase

Diploid (2n) condition consisting of 4 DNA molecules, with 2 chromatids per molecule.

Non-kinetochore Microtubules

Spindle fibers that do not connect to chromosomes, but instead interact and attach to each other from opposite poles.

Kinetochore Microtubules

Spindle fibers that attach directly to the kinetochore proteins located at the centromeres of the chromosomes.

Chromosome Connection in Prometaphase

Sister chromatids become connected to opposite poles of the cell by microtubule attachments.

Chromosome Movement in Prometaphase

Chromosomes begin actively migrating toward the metaphase plate (the cell's equator).

Prophase (Mitosis)

The first stage of mitosis where chromosomes condense

Chromosome State in Prophase

Diploid (2n) condition consisting of 4 DNA molecules

S Phase (Interphase)

The stage between G1 and G2 where DNA replication and centriole duplication occur.

Centriole behavior in Prophase

Duplicated centriole pairs begin to move apart to opposite poles of the cell to organize the mitotic spindle.

Mitotic Spindle Formation

The assembly of microtubule spindles that begins during prophase to eventually separate sister chromatids.

Late Prophase / Prometaphase Transition

The final event of prophase marked by the breakdown of the nuclear membrane.

Pro-Metaphase Chromosome Structure

A condensed chromosome consisting of two sister chromatids joined at a centromere

Prometaphase (Mitosis)

The mitotic stage where the nuclear envelope is completely gone

Chromosome State in Prometaphase

Diploid (2n) condition consisting of 4 DNA molecules

Non-kinetochore Microtubules

Spindle fibers that do not connect to chromosomes

Kinetochore Microtubules

Spindle fibers that attach directly to the kinetochore proteins located at the centromeres of the chromosomes.

Chromosome Connection in Prometaphase

Sister chromatids become connected to opposite poles of the cell via microtubule attachments.

Chromosome Movement in Prometaphase

Chromosomes begin actively migrating toward the "metaphase plate" (the cell's equator).

Metaphase (Mitosis)

The mitotic stage where all chromosomes align along the equator and sister chromatids attach to opposite poles.

Spindle Checkpoint (Metaphase)

last chance to abort cell division before chromosomes are physically pulled apart.

Anaphase (Mitosis)

The stage where sister chromatids separate into independent DNA molecules and the cell becomes temporarily tetraploid (4n).

Kinetochore Microtubules in Anaphase

depolymerize (shorten) to pull sister chromatids toward opposite poles.

Non-kinetochore Microtubules in Anaphase

polymerize (lengthen) to push cell poles further apart

Telophase (Mitosis)

final mitosis stage where chromosomes decondense and cluster at opposite poles. Nuclear envelope reforms and cytokinesis begins

Cytokinesis

The physical division of the cell cytoplasm that begins by cell furrowing (wrinkle)

Binary Fission

cell cycle and division in prokaryotes that produces two genetically identical daughter cells from 1 chromosome.

Mitosis vs. Meiosis

Mitosis produces identical cellular clones for growth/maintenance. Meiosis introduces genetic variation for sexual reproduction.

Human Karyotype

profile of a human chromosomes

Meiosis I

separates homologous pairs to generate haploid cells, each DNa molecule exists as a pair of sister chromatids

Meiosis II

separates sister chromatids to generate haploid gametes, each with a single copy of each DNA molecule

Prophase I

homologous chromosomes are brought tightly together(synapse) to form tetrads.

Homologous Recombination (Crossing Over)

precise breakage and reunion to mix non sister chromatids

Prometaphase I

homologous chromosomes randomly attach to kinetochore microtubules to separate maternal and paternal strands

Sister Chromatid Attachment (Prometaphase I)

Unlike mitosis sister chromatids of each individual chromosome are attached to the same pole.

Metaphase I

homologous chromosomes align along the cell equator facing opposite poles.

Anaphase I

homologous pairs are separated and moved to opposite poles

Reductional Division Outcome

The reason Meiosis I halving the chromosome number creates haploid daughter cells because homologous pairs have been separated.

Meiosis II Replication

No DNA replication happens between meiosis I and meiosis II.

Meiosis II vs Mitosis

The process of meiosis II and mitosis is otherwise functionally similar.

Anaphase II

The stage of meiosis II where sister chromatids are finally separated.

Meiosis II End Products

Four non-identical haploid gametes are produced containing a single chromatid/DNA molecule per chromosome.

Why Gametes are Non-Identical

Because genetic diversity was previously introduced by crossing over and random assortment.

Sources of Gamete Diversity

Genetic recombination (new DNA molecules) and independent assortment (increased combination diversity).

Random Fertilization (Syngamy)

The random fusion of gametes that further increases diversity by generating completely new homologous pairs.

Fertilization Ploidy Outcome

Restores the diploid number of chromosomes in the next generation's zygote.

Homologous Chromosome Alignment

align perfectly with each other during prophase I to facilitate crossing over.

Genetic Exchange Outcome

Creates completely new chromatids with various combinations of hundreds of different genes/alleles.