Cell Division Flashcards
(41 cards)
What are chromosomes?
- DNA, protein, little bit of RNA
- DNA is made up of small sections called genes
- found in matching pairs called homologous chromosomes in diploid cells
How many chromosomes do humans have?
23 pairs of homologous chromosomes
Each homologous pair has one chromosome inherited from the mother (maternal), and one chromosome inherited from the father (paternal)
What is a diploid and haploid cell?
- total number of chromosomes in a somatic body (cell) is the DIPLOID number, as there are two of each type of chromosome
- gametes are haploid cells, as they have one of each type of chromosome (half the diploid number)
What happens during interphase?
- DNA replicates (during s-phase)
- organelles reproduced so each daughter cell has the same number
- protein synthesis occurs, including producing the enzymes required for cell division (DNA helicase, DNA polymerase)
- ATP synthesis occurs in mitochondria during aerobic respiration
What happens during each phase of interphase?
G1:
- cell gets bigger and more rounded
- organelles replicated
- protein and ATP synthesis
S-phase:
- DNA is replicated inside the nucleus
- DNA content doubles
G2:
- protein synthesis continues
- centrioles replicate (only inside animal cells)
What is mitosis?
The division of the nucleus that occurs in 4 phases
- prophase
- metaphase
- anaphase
- telophase
What happens during prophase?
- chromatin condenses so it is now possible to see the replicated chromosomes
- centriole pairs migrate towards opposite poles of the cell to make the mitotic spindle
- nucleolus inside nucleus breaks down and disappears
-nuclear envelope made of two phospholipid bilayer now breaks down and disappears - replicated chromosomes attach to the mitotic spindle by their centromeres
Longest stage
What happens during metaphase?
- replicated chromosomes that are attached to the mitotic spindle now move along the spindle fibres, until all the chromosomes align down the equator of the cell
What happens during anaphase?
- the mitotic spindle fibres now contract (shorten), splitting the centromere
- the split centromeres get pulled to opposite poles of the cell, with a sister chromatid attached
- the sister chromatids end up at opposite poles of the cell
Fastest phase
What happens during telophase?
- nuclear envelopes now reform inside the cell around the separated sister chromatids (this cell has two nuclei in it now, each haploid)
- the nucleolus reappears inside each new nucleus
- the spindle fibres break down
What happens during cytokinesis in animal cells?
Contractile proteins in the cytoplasm shorten, pulling the cleavage furrow inwards, when the membrane fuses two genetically identical diploid daughter cells are formed
What happens during cytokinesis in plant cells?
A cell plate forms across the equator of the parent cell from the inside outwards, and a new cellulose cell wall is laid down
What are differences between plant and animal cells in mitosis?
- animal cells become more rounded before mitosis, whilst plant cells do not change shape due to the strong cellulose cell wall
- animal cells contain centrioles, whereas plant cells have no centrioles
- in cytokinesis in animal cells, a cleavage furrow forms from the outside inwards and pinches the cytoplasm (due to contracting proteins), whereas in plant cells, the cell plate develops from the centre outwards, forming a new cellulose wall
- in animal cells, the cell spindle degenerates at telophase as two new nuclei form, whilst in plant cels, the spindle remains throughout new cell wall formation
- in animal cells, mitosis occurs in epithelial tissue, bone marrow, and other sites, whereas in plant cells mitosis occurs at the meristems (tips of roots and shoots)
Why is mitosis significant?
- produces two daughter cells with the same number of chromosomes as the parent cell
- each chromosome is an exact replica of one or the original parent chromosomes, so mitosis produces cells that are genetically identical to the parent cell, ensuring genetic stability
What are the functions of mitosis?
- growth of an organism
- repair of damaged tissue
-replacement of dead cells
How do asexual plants reproduce?
Produces offspring by mitosis, so offspring are genetically identical to the identical to the parent
No genetic variation = they are clones
Large numbers of genetically identical offspring are produced by strawberry runners, daffodil bulbs and potato tubers
What are the advantages of asexual reproduction?
- offspring are genetically identical to the parent, so they are able to survive successfully if the environmental conditions remain stable
- less time and energy are required as there is no need to produce gametes and find a reproductive partner
- population can rapidly increase in number if environmental conditions are stable
What are the disadvantages of asexual reproduction?
- lack of genetic variation means offspring cannot adapt to changing environmental conditions
What are carcinogens?
Radiation, some chemicals, some viruses that can mutate DNA and affect the genes that control the cell cycle
What do proto-oncogenes do?
Regulate the cell cycle by signalling when cells should divide
What are oncogenes?
A mutated proto-oncogene that leads to uncontrollable cell division meaning tumour formation
What types of tumour can form?
Benign = non-cancerous, won’t invade nearby tissues
Malignant = cancerous, can spread to other tissues
What are tumour suppressant genes?
A DNA base sequence that codes for the correct primary structure of a tumour suppressant protein (correct tertiary structure) so the protein acts as a ‘brake’ on the cell cycle, causing it to slow down = if mutation in DNA, then this will not occur, and there will be unregulated cell division causing cancer cells
What is meiosis?
Produces gametes in sexually reproducing organisms, resulting in four genetically different daughter cells
Involves two stages of cell division-
Meiosis I = chromosome number is halved
Meiosis II = haploid cells divide again, producing four genetically different daughter cell (similar to mitosis)
