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AS Biology > Chapter 5: Mitotic Cell Cycle > Flashcards

Chapter 5: Mitotic Cell Cycle Flashcards

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1
Q

Define a stem cell

A

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

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2
Q

What is potency

A

Extent of power of stem cell to produce different cell types

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3
Q

3 types of stem cells based on potency

A

Totipotent
Embryonic or pluripotent
Multipotent

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4
Q

What is Totipotent

A

Stem cell that can produce any type of cell
Most potent
Eg zygote formed by sperm and egg fusion

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5
Q

What is embryonic or pluripotent

A

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

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6
Q

What is Multipotent

A

Stem cell that produces few types of cells

Eg haematopoietic

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7
Q

Example of Multipotent stem cells and 2 types of it

A

Haematopoietic
Myeloid progenitor : eosinophil, RBC, basophil, neutrophil
Lymphoid progenitor : B-lymphocyte, T-lymphocyte

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8
Q

Define stem cell therapy

A

Introduction of new adult stem cell into damaged tissue to treat a disease or injury

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9
Q

What is bone narrow transplantation

A

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

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10
Q

What is cancer

A

Uncontrolled cell division of cancerous cells resulting in irregular mass of cells called tumor
Does not show property of contact inhibition

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11
Q

Reason for cancer

A

Mutation in any gene (protooncogene) due to carcinogens (cancer causing substance) resulting in mutated cancer causing gene (oncogene)

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12
Q

Carcinogen egs

A

Uv light
Tar in tobacco smoke
Asbestos
X rays

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13
Q

Explain mechanism of cancer

A

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

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14
Q

Differences between benign and malignant tumors

A

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

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15
Q

Stages of mitosis:

A 
Nuclear division:
Interphase 
Early prophase 
Late prophase 
Metaphase 
Anaphase 
Telophase
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16
Q

Explain interphase, and early prophase

A

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

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17
Q

Explain late Prophase

A

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

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18
Q

Explain Metaphase

A

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

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19
Q

How are chromosomes separated in Metaphase

A

Each chromosome splits at centromere
Forms 2 separated chromatids with separate centromeres but attached at ends
Chromatids start to be pulled apart by microtubules

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20
Q

Explain Anaphase

A

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

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21
Q

Explain Telophase

A

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

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22
Q

What happens after Telophase

A

Cytokinesis

Division of cytoplasm and cell into two by constriction of edges of cell

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23
Q

What is cell cycle

A

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

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24
Q

Stages of cell cycle

A

G1 - gap 1
S - synthesis
G2 - gap 2
M - mitosis

G1, S, G2 is interphase

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25
Q

What happens in G1

A
  • 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.
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26
Q

Dna and chromosome content in G1

A

Dna 2C

Chromosome 2n

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27
Q

G0 phase?

A

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

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28
Q

Where is G0 permanent and where can it restart

A

Heart never eye cells

May restart if they get right signal

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29
Q

S phase :

A

Dna replication in the 46 chromosomes so each consists of 2 identical chromatids

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30
Q

Dna and chromosome content in S phase

A

Dna is 4C

Chromosome is 2n

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31
Q

G2 phase

A
  • 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
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32
Q

Define mitosis

A

Nuclear division followed my cytoplasmic division

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33
Q

How is cell cycle regulated/controlled

A

Checkpoints at different stages

34
Q

Why is regulation of cell cycle important

A

Detect cell with damaged DNA and either repair it or cell containing it undergoes apoptosis (cell death)

35
Q

What happens at G1 checkpoint

A

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

36
Q

What is p53 tumour suppressor gene?

A

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

37
Q

What is Rb tumour suppressor gene?

A

Retinoblastoma
Function: inhibit cell cycle progression until cell ready to divide.
Inactivated Rn protein is unable to control cell proliferation (increase in no)

38
Q

What happens at C2

A

Located towards end of G2

Ensures all chromosomes have relocated and that replicated dna is no OT damage before cell enters M phase

39
Q

What is G3 or M cp

A

Located in mid of M phase

Ensures all sister chromatids are correctly attached to spindle before cell enters Anaphase

40
Q

what is diploid

A

2 sets of chromosomes ie 2n 46chromosomes

41
Q

what is haploid

A

n 23chromosomes germ/sex cell

42
Q

all body cellls are

A

somatic eg skin

43
Q

nature and function of centromere

A 
nature: dna
function:
-helps in separation of chromatids
-acts as site of spindle attachment
-region where chromatids are located
44
Q

what is a kinetochore

A

protein molecules, disc like structure, bind to DNA in centromere originating from poles

45
Q

location of kinetochore

A

each metaphase chromosome has 2 kinetochores at centromere ie 2/chromosome

46
Q

function of kinetochore

A

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

47
Q

centrosome

A

organelle that acts as MTOC for spindle fibre construction in animal cells. consists of centrioles. absent in plant cells

48
Q

4 ways mitosis is significant?

A

growth, immune response, replacement and repair of cells/tissue, asexual reproduction

49
Q

mitosis and growth

A

2 daughter cells have same chromosome no as parent cell and are genetically identical (clones). allows growth of multicellular organisms from unicellular zygotes

50
Q

mitosis and immune response

A

cloning of B and T lymphocytes during immune response

51
Q

mitosis and replacement and repair of cells/tissues

A

cells constantly die and are replaced by identical cells produced by mitosis. some animals able to generate whole parts of body

52
Q

mitosis and asexual reproduction

A

involves only one parent. offspring identical to eachother and also to parent. called clone

53
Q

gametes involvement in asexual reproduction

A

with is spores eg fungi penicillium, without eg budding in hydra

54
Q

asexual reproduction in plants

A

vegetative propagation.

55
Q

How is DNA, total 1.8m long and 2nm wide made of 46 chromosomes, packed into nucleus fo 6Mm diameter?

A

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

56
Q

nucleosome:

A

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

57
Q

difference between euchromatin and heterochromatin

A

eu-loosely coiled, has active genes, lightly stained

hetero- tightly coiled, inactive genes, densely stained (it is not the nucleolus)

58
Q

what are telomeres

A

structures that seal chromosome end. made up of dna with repeated short base sequences. one strand is guanine rich, other of cytosine.

59
Q

which enzyme is used to add telomeres

A

telomerases

60
Q

importance of telomeres

A

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

61
Q

how is vital gene loss prevented by telomeres

A
  • 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
62
Q

why are telomeres repeated GC sequences and not AT?

A

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

63
Q

what is base substitution mutation

A

swapping one nucleotide with another

64
Q

3 types of base substitution mutations

A

silent
mis sense
nonsense

65
Q

what is silent mutation

A

this happens at the 3rd position of sequence and there is no change in the code ie still codes for same amino acid

66
Q

what is mis sense mutation

A

when this happens it results in a codon that specifies a different amino acid and hence different polypeptide/protein

67
Q

what is nonsense mutation

A

results in a stop codon which halts translation and results in a non functional protein

68
Q

which are the stop codon

A

UAA
UAG
UGA
(UAU works)

69
Q

3 features of a genetic code

A
  • 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
70
Q

differ between coding and template strand

A
  • 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
71
Q

define transcription

A

mRNA is synthesized 5’-3’ direction complementary to template strand of 3’-5’ DNA by RNA polymerase enzyme

72
Q

explain the process of transcription

A
  • 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
73
Q

what it translation

A

decoding mRNA and using its info to build a polypeptide/chain of aa

74
Q

what are codons and anti codons

A

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

75
Q

which is start codon

A

AUG

76
Q

3 stages of translation

A
  • initiation
  • elongation
  • termination
77
Q

explain initiation

A
  • 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’
78
Q

what are raw materials for translation

A

ribosomes with its 2 subunits, mrna instruction, initiator tRNA ie carrying 1st aa called methionine

79
Q

explain elongation

A
  • 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
80
Q

explain termination

A

polypeptide chain grows until stop codon is exposed at A site of ribosome

AS Biology (11 decks)

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