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composition prokaryotes + types

Cell wall
Plasma membrane
Prokaryote include at least 2 distinct types of bacteria:
1. Bacteria (eubacteria)
Archaea (ancient bacteria)

Unicellular, no membrane bound organelles
Prokaryotic DNA doesnt exist in the highly ordered packed arrangment (LOOSELY PACK)
Made up of eubacteria and archaea


composition of eukaryotic cell + 3 characteristics

- Nucleus
- Nuclear envelope
- Endoplasmic reticulum
- Ribosomes
- Mitochondrion (animals)
- Vacuole (plant)
- Chlorplast (plant)
- Golgi apparatus
- Plasma membrane
Cell wall (plant)

- Both unicellaur and mutlicellular with membrane-bound organelles
- Genetic material is surrunded in a nuclear envelope to form a nucleus
DNA is closely asscociayed with histones to form tightly packed chromosomes


prokaryotic vs eukaryotic cell: nucleus

Pro: absent
euk: present


prokaryotic vs eukaryotic cell: cell diameter

pro: relatively small, from 1 to 10 um
euk: relatively large, from 10 to 100 um


prokaryotic vs eukaryotic cell: genome

pro: usually one circular DNA molecule
euk: multiple linear DNA molecules


prokaryotic vs eukaryotic cell: DNA

pro: not complexed with histones in bacteria; some histones in archaea
euk: complexed with histones


prokaryotic vs eukaryotic cell: amount of DNA

pro: relatively small
euk: relatively large


prokaryotic vs eukaryotic cell: membrane-bounded organelles

pro: absent
euk: present


3 fundamental events in cell reproduction

1. Genetics information must be copied
2. The copies of genetic information must be separated from each other
3. The cell must divide

** the processes that lead to these events differ in prokaryotic & eukaryotic cells because of their structural differences


steps of prokaryotic cell reproduction

1. As the chromosomes replicate, the origins segregate to opposite sides
** replication usually begins at a specific place on the chromosome called the origin of replication
2. The origins of replication move away from each other and toward opposite ends of the cell
The cell divides. Each new cell has an identical copy of the original chromosome


what are homologous chromosomes

In most eukaryotic cells (not all like in plants, chromosomes occur as pairs)
- Each set of chromosomes is a homologous pair
- One member of each homologous pair is inherited from the male parent, the other member from the female parent
- Look alike, have the same lenght and centromere position, and have a similar banding pattern when stained
- A location on one homologue contains genes for the same trait that occurs at this locus on the other homologue, although the genes may code for different variations of that trait *called alleles

Eukaryotic chromosomes:
- Linear
- Every specie hs different number of chromosomes
- Composed of CHROMATIN - a complex of histones and DNA


locus, gene and allele

Locus: physical place on the chromosome
We have genes on the locus, and when we have diffrent versions of the same gene, we called it allele


chromatide vs chromatine

Chromatid vs chromatine:
Une chromatide (Cht) est une molécule d'ADN (le nucléofilament) associée à des protéines histones (PH) et des protéines non-histones (PNH). Une chromatide a la forme d'un bâtonnet qui peut avoir différents degrés de condensation suivant les moments du cycle cellulaire ou l'activité de transcription des gènes.
Cette unité structurale n'apparaît en tant que chromosome que durant les divisions cellulaires (mitose ou méiose). Le reste du temps, l'ensemble des chromatides forme la chromatine


centromere, telomere,

Centromere: not the middle portion, can be almost everywhere, they have nothing special its just how the DNA is wrapped and packaged very tight (the sequence is not special, its only the way it is packaging)
** the chromosome without a centromere cant be drawn into the newly formed nuclei, so these chromosomes are just lost

Telomeres: ends of chromosomes, prokaryotic doesnt have one because its a circular DNA, so need to be linear to have a top and a bottom. When you have sister chromatide = double the number of telomere
** it protects and stabilize the chromosome ends + participating in eliminating cell division and play an important role in aging anc cancer

** chromosomes are attached to the microtubules by the kinetochore, always follow it

Spincle microtubules: filaments responsible for moving chromosomes during cell division.


4 major types of chromosomes based on the centrome position



cellular reproduction involves 2 important processes

1. GROWTH: involves duplication of the cells DNA and contents
2. CELL DIVISION: involves the separation of the cells DNA and content into daughter cells


the cell cycle (interphase + M phase)

INTERPHASE: an extended period between cell divisions, DNA synthesos, anc chromosome replication phase

Interphase: G1, S, G2
1. G1: cells grow and proteins necessary for cell division are synthesized (several hours)
2. G1/S chekpoint: make sure the cell is hold in G1 until the cell has all the enzyme necessary for the replication of DNA.
** some cells may go in G0 where they keep the exact same size (dont grow), which is a stable state. They can remind there or reenter to G1 or just never go there
3. S: DNA syntesis, in which each chromosome is duplicated. The DNA synthesis must take place before the mitosis. So after the S phase, each chromosome is composed of 2 chromatides.
4. G2: several additionnal biochemical events necessary for cell division take place
5. G2/m checkpoint: the cells pass only if the cells DNA is completely replicated and undamaged (if yes, they can inhibit the activation of some proteins necessary for mitosis)
** during interphase= chromosome is in a relax mode

M PHASE: mitotic phase: (the process of nuclear division) and cytokinesis (cytoplasmic division)
The part of the cycle where the sister chromatids separate and cells undergoes division


6 phases of mitosis

1. INTERPHASE: DNA is not condense
2. PROPHASE: DNA is condensed in chromosomes and each is composed of 2 chromatids because they have been duplicated in the S phase.
- Formation of the mitotic spindle
3. PROMETAPHASE: nuclear membrane is desintegrated
- Spindle microtubules goe inside the nucleus and when it met a kinetochore, it is stabilized
- Each chromosome becomes attached to microtubules from opposite poles of the spindle
4. METAPHASE: precisely align in the middle
5. ANAPHASE *** very important for genetic!!!! : sister chromatides split apart
6. TELOPHASE: enough space between, the cell membrane will reform after the cytokinesis
- Reformation of the nuclear membrane
** after the sister chromatid have been separataed, they are considered 2 separated chromosomes
- The chromosome relax (not dense anymore)


number of chromosomes and DNA molecules through every step of the cell cycle

*** - The number of chromosomes per cell = the number of functional centromeres
- The number of DNA molecules per cell = the number of chromatids

- 2 complete sets of chromosomes, so 4
- DNA is unreplicated (no sister chromatids) so 4 DNA molecules
- Each DNA is copied to form sister chromatids so 8 DNA
- But even if its double, still 4 chromosomes because the copies have the same centromere!!!
- 4 chromosomes and 8 DNA molecules

- Separation of the sister chromatids so each has is own centromere so 8 unreplicated chromosomes!!!
- 8 DNA molecules

AFTER CYTOKENESIS (formation of the cytoplasm):
- The 8 DNA are distributed equally within 2 cells, so each cell has 4 DNA molecules and 4 chromosomes (same as the beginning of the cycle)

- Number of chromosomes increases in anaphase and decrease through cytokenesis
- Number of DNA molecules only in the S phase and decreases through cytokenesis


role of cohesins

Metaphase: one chromosome with 2 sister chromatidess. There will be one point where the cohesins (proteins) will not be stable so it will separate.
So cohesins have the role to decide if the chromatid stays together or not

** centromere is the last place where it separates (very tight DNA)


genetic consequences of the cell cycle

- Producing 2 cells that are genetically identical to each other and with the cell that gave rise to them
- Newly formed cells contain a full complement of chromosomes
- Each newly formed cell contains APPROXIMATIVELY half the cytoplasm and organelle content of the original parental cell
The nucleus is not the only source of genetics in the cell, we also have the mitochondria and in the chloroplasts and those are not doing the mitosis process, so they will be separate in half (approximatively)