Chapter 5: Mitotic Cell Cycle Flashcards
Define a stem cell
Cell that can divide unlimited no of times by mitosis, each new cell has potential to remain a stem cell or develop into a specialised cell
What is potency
Extent of power of stem cell to produce different cell types
3 types of stem cells based on potency
Totipotent
Embryonic or pluripotent
Multipotent
What is Totipotent
Stem cell that can produce any type of cell
Most potent
Eg zygote formed by sperm and egg fusion
What is embryonic or pluripotent
Stem cell that can lose ability to form placenta
Can form all cells that lead to embryo development
Totipotent - placenta = embryonic
Eg fertilised egg at 16 cell stage
What is Multipotent
Stem cell that produces few types of cells
Eg haematopoietic
Example of Multipotent stem cells and 2 types of it
Haematopoietic
Myeloid progenitor : eosinophil, RBC, basophil, neutrophil
Lymphoid progenitor : B-lymphocyte, T-lymphocyte
Define stem cell therapy
Introduction of new adult stem cell into damaged tissue to treat a disease or injury
What is bone narrow transplantation
Medical procedure performed to replace damaged bone marrow (by disease/infection). Involves transplanting blood stem cells which travel to bone marrow where they produce new blood cells to promote bone marrow growth
What is cancer
Uncontrolled cell division of cancerous cells resulting in irregular mass of cells called tumor
Does not show property of contact inhibition
Reason for cancer
Mutation in any gene (protooncogene) due to carcinogens (cancer causing substance) resulting in mutated cancer causing gene (oncogene)
Carcinogen egs
Uv light
Tar in tobacco smoke
Asbestos
X rays
Explain mechanism of cancer
Carcinogen causes mutations
1) normal cell transformed to cancer cell by carcinogen as oncogene forms
2) cancer cell does not respond to signal from other cells so continues to divide-contact inhibition property lost. Doesn’t undergo early death by bodys immune system
3) uncontrolled cell division by mitosis
4) cells absorb nutrients and undergo rapid mitosis
5) tumor gets bigger, nutrients decreasing so outer cells become loose. Cells chnage characteristics-look different. Results in localised, benign, tumor
6) tumor supplied with blood and lymph vessels so growing tumor gets nutrients and increases in side
7) cancer cells break from tumor and spread into fluids and move to other body parts. Results in malignant tumor
8) metastasis. Tumor cells invade tissues. Secondary cancers form throughout body
Differences between benign and malignant tumors
B- localised ie do not spread from site of origin. Treated by surgery
M- invade other tissues by blood lymph forming secondary cancer. Treated by chemo or radiation therapy
Stages of mitosis:
Nuclear division: Interphase Early prophase Late prophase Metaphase Anaphase Telophase
Explain interphase, and early prophase
Inter: cell normal. Chromatin network present. Centrosome normal.
Early: chromatin network condenses to form chromosomes. Centromeres with attached kinetochores. Centrosome replicates just before prophase. Nuclear membrane, nucleolus intact
Explain late Prophase
1) centrosomes start moving to opp poles where they form spindle fibres
2) nuclear envelope breaks into small vesicles (invisible under microscope) nucleolus also disappears as forms part of chromosomes
Chromosomes seen to consist of 2 identical sister chromatids attached at centromere. Each chromatin has 1 DNA molecule which replicates to give sister chromatids
Explain Metaphase
1) centrosomes reach poles and spindles arise from them and join to chromosomes
2) nuclear membrane and nucleolus fully gone
3) chromosomes arranged in equitorial plate. Centromere at each chromosome attached to spindle from centrosome
How are chromosomes separated in Metaphase
Each chromosome splits at centromere
Forms 2 separated chromatids with separate centromeres but attached at ends
Chromatids start to be pulled apart by microtubules
Explain Anaphase
1) chromosomes split at centromere and sister chromatids pulled apart by microtubules shortening at MTOC centrosome
2) sister chromatids pulled towards opp poles so that centromeres move towards centrosome first with arms trailing behind
Explain Telophase
1) sister chromatids have reached poles and undergo decondensation to form chromatin network
2) nucleolus and membrane reforming
3) remains of spindles break down
4) centrosomes will replicate again during next interphase before next nuclear division
What happens after Telophase
Cytokinesis
Division of cytoplasm and cell into two by constriction of edges of cell
What is cell cycle
Process a cell undertakes to replicate all it’s materials and divide into 2 identical daughter cells
Or
Regular sequence on events between two cell divisions
Stages of cell cycle
G1 - gap 1
S - synthesis
G2 - gap 2
M - mitosis
G1, S, G2 is interphase
What happens in G1
- Cell increases in size to distort nucleus to cytoplasm(+) ratio
- Cellular content duplicated. No of organelles and cytoplasmic content increase
- Cell makes RNA, enzyme, protein
- Longest in interphase
- At the end, cell commits to divide or to not.
Dna and chromosome content in G1
Dna 2C
Chromosome 2n
G0 phase?
Some cells of the ones either constantly dividing or at rest may enter resting state where cell is performing function without actively preparing to divide
Where is G0 permanent and where can it restart
Heart never eye cells
May restart if they get right signal
S phase :
Dna replication in the 46 chromosomes so each consists of 2 identical chromatids
Dna and chromosome content in S phase
Dna is 4C
Chromosome is 2n
G2 phase
- Cell grows more
- Organelle and proteij synthesis happens in preparation of mitosis. Sharp increase in production or protein Tubulin which is needed to fork microtubules of spindles
- New dna checked and any errors found repaired
Define mitosis
Nuclear division followed my cytoplasmic division
How is cell cycle regulated/controlled
Checkpoints at different stages
Why is regulation of cell cycle important
Detect cell with damaged DNA and either repair it or cell containing it undergoes apoptosis (cell death)
What happens at G1 checkpoint
Located at end of G1 phase. Cell decides whether or not to proceed with cell division based on factors such as cell size, nutrients, growth factors, dna damage
What is p53 tumour suppressor gene?
Used in G1 cp or C1
p53 protein produced from p53 gene. Regulates cell division by keeping cells from growing and dividing too fast, or in uncontrolled manner.
If any damaged dna found either progress of cell cycle is arrested at C1 to repair or apoptosis
What is Rb tumour suppressor gene?
Retinoblastoma
Function: inhibit cell cycle progression until cell ready to divide.
Inactivated Rn protein is unable to control cell proliferation (increase in no)
What happens at C2
Located towards end of G2
Ensures all chromosomes have relocated and that replicated dna is no OT damage before cell enters M phase
What is G3 or M cp
Located in mid of M phase
Ensures all sister chromatids are correctly attached to spindle before cell enters Anaphase
what is diploid
2 sets of chromosomes ie 2n 46chromosomes
what is haploid
n 23chromosomes germ/sex cell
all body cellls are
somatic eg skin
nature and function of centromere
nature: dna function: -helps in separation of chromatids -acts as site of spindle attachment -region where chromatids are located
what is a kinetochore
protein molecules, disc like structure, bind to DNA in centromere originating from poles
location of kinetochore
each metaphase chromosome has 2 kinetochores at centromere ie 2/chromosome
function of kinetochore
construction of it begins during s phase/before division and lost again after. microtubules attached to it pull it with rest of its chromatid dragging behind towards pole. this is by microtubule shortening both from pole end and from kinetochore end
centrosome
organelle that acts as MTOC for spindle fibre construction in animal cells. consists of centrioles. absent in plant cells
4 ways mitosis is significant?
growth, immune response, replacement and repair of cells/tissue, asexual reproduction
mitosis and growth
2 daughter cells have same chromosome no as parent cell and are genetically identical (clones). allows growth of multicellular organisms from unicellular zygotes
mitosis and immune response
cloning of B and T lymphocytes during immune response
mitosis and replacement and repair of cells/tissues
cells constantly die and are replaced by identical cells produced by mitosis. some animals able to generate whole parts of body
mitosis and asexual reproduction
involves only one parent. offspring identical to eachother and also to parent. called clone
gametes involvement in asexual reproduction
with is spores eg fungi penicillium, without eg budding in hydra
asexual reproduction in plants
vegetative propagation.
How is DNA, total 1.8m long and 2nm wide made of 46 chromosomes, packed into nucleus fo 6Mm diameter?
DNA is wound around proteins (nature:basic) called histones. basic histones interact with acidic DNA (presense of -vely charged phosphate group)
(elaborate on nucleosomes*)
10nm width DNA wrapped around nucleosome
nucleosome and linker DNA-beads on string form of chromatin are coiled into helix to form 30nm wide fibre called solenoid. has about 6 nucleosomes per turn of helix
solenoid can be further coiled, and super coiled and looped involving non histone acidic proteins that help in scaffolding the structure
nucleosome:
cylindrical in structure, 11nm wide, 6nm long.
made of 8 histone proteins: H2A, H2B, H3, H4- 2 of each that make histone octamer.
1(2/3)-147 bp of dna wrapped around nucleosome
linker dna- dna between nucleosomes. 53bp long and is stabilised by H1 histone protein
difference between euchromatin and heterochromatin
eu-loosely coiled, has active genes, lightly stained
hetero- tightly coiled, inactive genes, densely stained (it is not the nucleolus)
what are telomeres
structures that seal chromosome end. made up of dna with repeated short base sequences. one strand is guanine rich, other of cytosine.
which enzyme is used to add telomeres
telomerases
importance of telomeres
ensures that when dna is replicated the end of molecule is included the copying dna polymerase cannot run to end of dna to complete replication
prevents loss of vital gene, due to the lack of which results in cell death
how is vital gene loss prevented by telomeres
- they add extra multiple repeated sequences toend of chromosome and make dna bit longer
- these extra bases are added during each cell cycle
- ensures no vital genes lost, allows dna polymerase to complete replication
- some cells- specialised/differentiated do not top up telomeres each division. this results in telomeres getting shorter each division until vital dna is no longer protected, and cell death occurs
why are telomeres repeated GC sequences and not AT?
GC has triple bond between G and C which is much stronger than double bond in AT
repeated GC sequences ensures that the end of chromosomes are strongly sealed
what is base substitution mutation
swapping one nucleotide with another
3 types of base substitution mutations
silent
mis sense
nonsense
what is silent mutation
this happens at the 3rd position of sequence and there is no change in the code ie still codes for same amino acid
what is mis sense mutation
when this happens it results in a codon that specifies a different amino acid and hence different polypeptide/protein
what is nonsense mutation
results in a stop codon which halts translation and results in a non functional protein
which are the stop codon
UAA
UAG
UGA
(UAU works)
3 features of a genetic code
- specificity: particular codon codes for same amino acid
- redundancy: genetic code is virtually universal/has been conserved from early stages of evolution
- degeneracy: it is degenerate, each codon corresponds to single aa but given aa may have more than 1 genetic code
differ between coding and template strand
- coding: sense strand, 5’-3’, no role in transcription, base sequence=mRNA
- template: anti sense, 3’-5’, strand on which mRNA is transcribed in 5’-3
define transcription
mRNA is synthesized 5’-3’ direction complementary to template strand of 3’-5’ DNA by RNA polymerase enzyme
explain the process of transcription
- RNA polymerase binds at promoter
- DNA unwinds and unzips as H bonds between bases break. 2 strands formed
- free activated RNA nucleotides pair up complementary to sense/template in 5’-3’ catalysed by RNA polymerase as it bonds sugar & phosphates to form backbone and ends at terminator sequence
- 2 phosphates broken off released to nucleus
- single stranded mRNA leaves via nuclear pore
what it translation
decoding mRNA and using its info to build a polypeptide/chain of aa
what are codons and anti codons
codon- in mrna, the institution for building polypeptide come in groups of 3 nucleotides ie the genetic code
anti-set of 3 nucleotides that bind comp. to mrna codon via base pairing
which is start codon
AUG
3 stages of translation
- initiation
- elongation
- termination
explain initiation
- in cytoplasm there are free aa and tRNA
- tRNA has 2 sites: for aa binding ie CCA at 3’ end (5’ end has phosphate). other is anticodon (base triplet of unpaired bases)
- tRNA specific to aa under conditions: amino-acyl tRNA synthetase enzyme and energy from ATP
- mrna binds to small s.u, 6 bases at a time exposed to large s.u. first 3 at P site and next 3 at A site of large ribosomal subunit.
- first 3 are always AUG t P site
- tRNA with comp. anticodon, UAC, (aa; Met) forms H bonds with codon. initiator tRNA
- tRNA reads 5’-3’
what are raw materials for translation
ribosomes with its 2 subunits, mrna instruction, initiator tRNA ie carrying 1st aa called methionine
explain elongation
- second trna binds with next 3 bases at A site of large s.u and brings a diff aa
- 2 aa held closely, peptide bond forms; reaction catalysed by enzyme peptidyl transferase which is found in small s.u
- after aa attaches trna leaves
- ribosome moves along and reads mrna in 5’-3’ and calls trna
explain termination
polypeptide chain grows until stop codon is exposed at A site of ribosome
