Cell division Flashcards
1
Q
What are chromosomes
A
- consist of DNA and a protein called histone and are only visible after they condense at one set of cell division
- following DNA replication chromosome exists as two identical sister chromatids joined by a centromere
- sister chromatids are genetically indentical
- each chromosome containes genes that code for a specific polypeptide
2
Q
what are homologous pairs
A
contain same genes may be different version of alleles
3
Q
how many pairs of chromosomes in humans
A
- 23
- one from each parent
4
Q
What does diploid mean
A
- where an organism has two complete sets of chromosomes
- so in humans diploid = 46
5
Q
What does haploid mean
A
- half the number of sets of chromosomes so in human gametes and in some organisms
- in human gametes = 23
6
Q
What is the cell cycle
A
- majority of cell cycle in eukaryotes involves interphase where DNA, proteins and organelles are synthesised
- followed by four stages of mitosis where chromosomes are arranges and seperated prior to formation of two genetically identical cells via cytokenesis
7
Q
What is interphase
A
- longest phase in the cell cycle is very metabolically active
- quantity of DNA doubles chromosome number the same as chromosomes exist as two sister chromatids joined togehter by a centromere
- protein synthesis and organelle replication occurs requiring much ATP
8
Q
What is mitosis
A
- results in production of two genetically identical cells
- important in growth and repair when differentiated cells replicate
9
Q
What occurs in prophase
A
- chromosomes condense to become shorter and thicker
- chromsomes become visible two sister chromatids attatched by the centromere
- centrioles move to opposite poles
- nuclear envelope disintegrates
- nucluousl dissappears
10
Q
What occurs in metaphase
A
- spindle forms
- chromosomes align at equator of cell attatched to spindles microtubules via centromere
11
Q
What occurs in anaphase
A
- spindle fibres shorten
- centromeres divide and chromatids pulled towards opposite poles
12
Q
What occurs in telophase
A
- chromatids reach piles and become indistinct by uncoiling
- nuclear envelope reforms
- nucleoulus reforms
- spindle fibres disintergrates
13
Q
What is cytokenesis
A
- division of cytoplasm in two distinct cells is different in animal and plant cells
- in animal cells the membrane inforlds via a cleavage furrow until two cells become sperated
- plant cells prescence of cellulose cell wall prevent from happening so instead a cell plate develops from the centre outwards till cell divided into two
14
Q
What is the significance of mitosis
A
- organisms can grow repair tissues and replace dead cells
- in animals skin and blood cells are constantly being replced becaue they wear out
- plant cells at root and shoot tips meritems are constantly undergoing mitosis
- important in asexual reproduction where genetically indentical offspring can be produced resulting in rapid increase in numbers during fabourable conditions ef yeast, bacteria and strawerberries where runners are produced
15
Q
What is the mitotic index
A
- mitotic index ration of number of cells undergoing mitosis to measure growth
16
Q
How is mitosis controlled
A
- by a nymber of genes including proto-oncogenes
- where a mutation in one of genes from chemicals eg benzene or UV turn into oncogenes resulting in uncontrollable cell division leading to formation of tumoir and cancers
- vistricistine prevents formation of spindle arresting mitosis at metaphase slowig rate of division treating cancers
17
Q
What i the length of interphase if 16 out of 12 cells are in the stage
A
- 16/20 = 80%
- 24 x 0.8 = 19.2 hrs
18
Q
What is meiosis
A
- two consecutive cell divisions four genetically different haploid cells
- occur in reproductive organs in animals plants and some protictista prior to sexual reproduction
- interphase occurs before prohpase I responsible for DNA replication and protein synthesis
19
Q
What occurs in meiosis I
A
- following interphase modified prophase I homolofous pairs come togehter to form bivalent crossing over may occur
- increases genetic variation
- other major differences occurs during metaphase when bivalent alignes randomly at equation known as independent assortment
20
Q
What occurs in interphase in meiosis
A
- occurs before meiosis
- DNA replicates
- 2N
- Dna content - 2
21
Q
What occurs in Prophase I
A
- crossing over can occur
- chromosomes condense to become shorter and thicker
- centrioles move to opposite poles (not in higher plants )
- chromosomes come together in homologous pairs (bivalent)
- crossing over occurs in part of one chromatis is exchanging with another
- nucleolis and nuclear membrane dissappear
- DNA content - 4
- 2n
22
Q
What occurs in metaphase I
A
- bivalents align
- spindle forms
- homologous chromosome pairs (bivalent) align at the equator of the cel attatched to spindle microtubules via centromere
- alignment is random and is called independent assortment
- DNA content -4
- 2n
23
Q
What occurs in anaphase I
A
- chromosomes are pulled to opposite poles
- spindle fibres shorten
- bivalents sperate and chromosomes pulled to opposite poles
- DNA content - 4
- 2n
24
Q
What occurs in telophase I
A
- chromosomes reach poles
- in some cases :
- nuclear envelope reforms
- nucleus reforms
- spindle dissintegrates
- DNA content - 4
- 2n
25
What occurs in cytokenesis I
* division of cytoplasm occurs creating two haploid cells
* DNA content -2
* n
26
What occurs in prophase II
* centrioled sperate and arrange at 90 degrees to previous spindle
* DNA content - 2
* n
27
What occurs in metaphase II
* chromosomes align at equator of cell attatched to spindle microtubules via centromere
* DNA content -2
* n
28
What occurs in anaphase II
* spindle fibres shorten
* centromere divide and chromatids are pulled towards opposite poles
* DNA content -2
* n
29
What occurs in telophase II
* chromatids reach poles and become indistinct
* nuclear envelope reforms
* nucleolus reforms
* spindle disintegrates
30
What occurs in cytokenesis II
* four haploid daughter cells produced
* DNA content - 1
* n
31
What is the significance of meiosis
* creates genetic variation through crossing over (prophase 1) and independent assortment (metaphase 1 and 2)
* keeps chromosome number constant by producing haploid gametes that can recombine during fertilisation restoring diploid number in the zygote
32
What is the difference between mitosis and meiosis
* mitosis:
* one cell division
* produces gentically identical cells
* cells are diploid
* no crossing over
* no independent assortment
* meiois:
* two cell divisions
* produce genetically different cells
* cells are haploid
* crossing over occurs in prophase I
* independent assortement occurs in metaphase 1 and 2
33
Gene
a base sequence of DNA that codes for the amino acid sequence of a polypeptide each gene occipoes a fixed position on the chromosomes called the locus
34
Homologous chromosomes
homologous chromosomes are the same size and shape and carry the same genes but these may be different versions called alleles one chromosome of each pair comes from each parent
35
Allele
* a different form of the same gene
36
Polyploidy
where an organissm has more than two complete sets of chromosomes
37
Interphase
a period of synthesis and growth during the cell cycle
38
Mitosis
involves four stages where chromosomes are arranged and seperated prior to cell division it results in two genetically identical cells that contain the same number of chromosomes as the parent cell
39
Cytokenesis
the division of the cytplasm to form two daughter cells following mitosis
