cell nuclear and cell devision

what are the phases in the cell cycle

G1 

S 

G2

M 

are G1/2 growth or gap phases

gap

what happens during the interphase phases ( G1, S, G2 )

1. G1: 

• Cell grows in size

• Synthesises proteins and organelles needed for S phase

• decides whether to go into S phase

 2. S: 

• DNA replicates makeing 2 sister chromotaids 

• histones and proteins synthesised

3. G2:

• cell prepares fro mitosis by growing more 

• check for error in DNA replication

What is the point at which growth factors re-enter or leave the cell called

Restriction point (R)- where the cell commits to going through cell division

What are the 5 stages of mitosis

1. Prophase

2. Prometaphase

3. Metaphase 

4. Anaphase

5. Telophase

describe the steps in cell division

1. prophase: 

   • Early prophase : Chromosomes condense, 

   • At late prophase, the chromosome condensation is complete and sister chromatids start to become visible. 

   • Spindle apparatus formed by microtubules

   • Structure is still in nuclear envelope

2. prometaphase 

   • Nuclear envelope breaks 

   • Chromosomes attach to kinetochores on spindle

3. metaphase: 

   • chromosomes line up on the microtubule spindle at the middle of the cell

   • they are ready to seperate

4. anaphase: 

   • sister chromotids seperate 

   • Cytokenis begins ( this is see by an actin band formed around the middle of the cell seperating the two daughter cells)

5. telophase: 

   • chromatid fully seperated 

   • chromatid decondense and form chromosomes 

   • spindle fibres disapear 

   • nuclear envelop ereforms 

   • nucleolus reform 

   • actin band contracts so the 2 cells begin to seperate

6. cytokensis : 

   • 2 cells seperate making 2 daughter cells

how long does cytokinesis take

1 hr

what stage are these cells in - 3 pics

1. Interphase

2. Early prophase

3. Late prophase

what stage is in this image - pic

Metaphase- chromosomes line up in the middle 

what stage of mitosis is this image in - pic

• Telophase- you can see the actin is starting to constrict it an dits not a fully cut so its not cyokenisis 

what stage of mitosis is this - pic

Prometaphase- the Nucleas isn’t intact so not prophase and the chromosomes are not in the middle yet so not metaphase 

what stage of mitosis is this - pic

• Anaphase- the chromosomes are pulled part to opposite poles 

what is meiosis 

A type of cell division that happens in germ cells (cells in the ovaries and testes) making the haploid gametes( sex cells)

what happens during meiosis 1 and 2

meiosis 1 

1. after dna replication (interphase) each chromosome has 2 sister chromatids

2. the homologous chromosomes pair up making bivalent pairs ( one chromosome from mum one from dad)

3. recombination( crossing over) happens when the homologous chromosomes swap pieces at the chismata( this is the point that they cross) this increases variation 

4. in anaphase 1 the homogenous chromosomes separate 

5. at the end there are 2 cells each haploid but the chromosomes are still duplicated 

meiosis 2 

1. no DNA replication before this 

2. In anaphase 2 the chromtids split at the centromere 

3. now theres 4 haploid gametes that are all genetically different 

steps of meiosis 

Meiosis I (reductional division):

1. Prophase I: homologous chromosomes pair (synapsis) and crossing over at chiasmata

2. Metaphase I: homologous pairs line up at the equator

3. Anaphase I: homologues separate to opposite poles

4. Telophase I & Cytokinesis: two haploid cells formed

Meiosis II (equational division, like mitosis):

1. Prophase II: chromosomes condense

2. Metaphase II: chromosomes line up at the equator

3. Anaphase II: sister chromatids separate

4. Telophase II & Cytokinesis: four haploid gametes produced

what are chiasmata

• points where homologous chromosomes cross over and exchange DNA

• Function: hold homologues together until anaphase I, then break to allow separation

What is random assortment of maternal and paternal chromosomes?

• During metaphase there is random assortment if their chromosomes which help with genetic variation

How does Genetic variation happen ( meiosis)

• crossing over: happens during prophase 1 making new combinations of maternal and paternal genes 

• random assortment increases genetic variation 

•  this makes there be genetic diversity in offspring 

How many different combinations of chromosomes and gametes are there

2^23 - chromosomes
8.4x10^6 - gametes

What are the differences between mitosis and meiosis

pic

What happens to the chromosome pairs during the formation of gametes and fertilisation

Meiosis: gametes get 23 chromosomes each
Fertilization: sperm + egg → 46 chromosomes (diploid)

how is DNA structured and packaged in chromatin

• DNA wraps twice around 8 histones making one nucleosome

• Histone H1 coils nucleosomes into 30 nm fibre

• Fibre forms loops attached to scaffold proteins

• Loops condense during mitosis to form visible chromosomes

explain the 2 different tightness of packaging of chromatin

• Euchromatin - loosely packed so more active so the genes are expressed

• Hetreochromatin - tightly packed so inactive and the genes aren’t expressed 

• The more condensed the chromotin the less transcriptional active 

draw a labeled chromosome, with kinetochore,centromere,chromatid

pic

how do you classify mitotic chromosoms

• through staining that amkes a banding pattern 

• through size

what are telomeres

• Telomeres: tandem repeats (GGGTTA in humans) at chromosome ends

• Functions:

  • Prevent chromosome fusion

  • Solve DNA replication end problem → telomerase adds repeats so important DNA isn’t lost during division

Where are telomerase expressed what is its functions

• Telomerase: enzyme that rebuilds telomeres

• Expressed in: germ cells and cancer cells; normally inactive in somatic cells

• Function:

  • Somatic cells → telomeres shorten → cell senescence

  • Cancer cells → telomerase active → telomeres maintained → unlimited division

What is a karyotype

• Organsisd display of all the chromosomes in a cell

• It is arranged by: size, number,shape and banding pattern 

• Banding pattern is shown using stains 

• This helps with classification as each species has a differnt karotype 

• It helps to detect genetic abnormalities 

How is the banding pattern in the karyotype useful

• Karyotype banding patterns: show characteristic chromosome stripes

• Use: detect large-scale chromosome changes (deletions, additions)

• Clinical relevance: helps identify diseases and affected chromosome regions

what are autosomes

non sex chromosomes

In somatic cells, where does each chromosome from the pair come from?

one maternal one paternal

what is aneuploid, heteroploid, polyploid cells and where are they found 

• Aneuploid = 1 chromosome off e.g 45 instead of 46

• Heteroploid = total number of chromosmes isnt a multiple of a haploid set ( incuding aneuploid)

• Polyploid = extra full sets e.g 3n 

• abnormal number of chromosomes

• cancer cell

what are the layers of the nuclear membrane

• The nucleus has double nuclear membrane 

  • Outer nuclear membrane is continuous with the endoplasmic reticulum

  • Inner nuclear membrane is supported by the nuclear lamina - a meshwork of filament protein called lamins

what is the structure and function of nuclear pore

• many proteins with aqueous chanel in the middle 

• used for communication between nucleas and cytoplasm 

how does transport through a nucleaas work

• Small molecules (under 9nm in diameter) like amino acids, nucleotides, short peptides are able to pass through the pores via passive diffusion

• Larger molecules require active transport

• Some proteins work in the Nucleas and have nuclear localisation sequences (NLS) which are short of amino acids which are recognised and allows the protein to enter the cell 

How do proteins with a Nuclear localisation signal get into the nucleus

• NLS is on proteins that need to work in the nucleas and it helps with entery 

• Cytoplasmic import receptors recognise the nuclear localisation signal  and transport the protein into the Nucleas 

• Inside the Nucleas the receptors release the protein using energy from the hydrolysis of GTP 

• The removal works the same way with the protein carrying a nuclear export signal  

What the nucleolus and what is the role of it

• Nucleolus: largest structure in the nucleus, usually central

• Role: transcribes rRNA and assembles ribosomal subunits

• Ribosomal subunits move to the cytoplasm for protein synthesis

label diagram: pic

pic