Eukaryotic Cell Cycle and Cell Division Flashcards
How are new cells formed?
The division of existing cells
What is binary fission?
Cell division in prokaryotic cells
What is the cell cycle?
Cell division in eukaryotic cells
What is asexual reproduction?
The formation of new organisms that doesn’t involve the fusion of gametes
What is a chromosome?
A series of nucleotide bases in DNA which holds genetic information
What is chromatin and what is an advantage of it?
DNA wrapped around histone proteins so that lots of DNA can fit in the nucleus
Describe the structure of a chromosome
Two sister chromatids joined by a centromere. They’re a fixed length
What is a centromere?
A narrow region along the length of the chromosome which occupies a specific region
What are the functions of the centromere?
To provide a site for the spindle fibres for the spindle fibres to attach to and to hold the sister chromatids together
What is a somatic cell?
Any cell apart from the gametes
What is a homologous pair of chromosomes?
A pair of chromosomes of the same size and shape which also have the same genes in the same order
What are diploid cells?
Cells which have homologous pairs of chromosomes as they have double the normal number of chromosomes
What is a karyotype?
The number and shape of the chromosomes in the somatic cell of an organism
What is a gene?
A sequence of DNA nucleotide bases that encodes the sequence of amino acids in a functional polypeptide
What is an allele?
Two or more different copies of the same gene
What is a homozygous cell?
A cell is said to be homozygous for a particular gene when identical alleles of the gene are present on both homologous chromosomes.
What is a heterozygous cell?
A diploid organism is heterozygous at a gene locus when its cells contain two different alleles of a gene.
What is a karyogram?
A drawing of the chromosomes of a cell arranged in homologous pairs and in numbered sequences
What is a sex chromosome?
A chromosome that carries genes that determine the sex of an organism
What is an autosome?
Any chromosome other than a sex chromosome
Name some conditions which may affect the length of the cell cycle
Temperature, supply of nutrients, supply of oxygen and the type of cell
Is the cell cycle the same length of time in all cells? Give examples
No. Cell cycle in the embryo has a shorter cell cycle than cells in the stomach.
What is the longest phase of the cell cycle?
Interphase
What are the phases in interphase?
First growth (G1), Synthesis, Second growth (G2)
How can you recognise cells in interphase?
Because no visible chromosomes can be seen
Describe what happens in G1
Genes switched on and base sequence transcribed onto pre-mRNA molecule which is then edited onto mature mRNA. Cytoplasm grows by producing new proteins and organelles.
Describe what happens in synthesis (S)
Semi-conservative replication of DNA. New histone proteins synthesised. Each chromosome becomes two chromatids joined by a centromere at the centre. Cell keeps growing
Describe what happens in G2
Replicated DNA checked for errors and errors corrected. If correction isn’t possible then the cell cycle is halted. Cell keeps growing
Name the four phases of mitosis
Prophase, Metaphase, Anaphase and Telophase
Describe the 5 things that happen in prophase
1) Chromosomes shorten and thicken by supercoiling, becoming visible
2) Nucleolus gradually disappears
3) Nuclear membrane disappears
4) Centrioles divide and move to the poles of the cell
5) Spindle fibres attach to the centromeres of the chromosomes
What are spindle fibres?
A network of microtubules which attach to the centromeres of the chromosomes
Describe what happens in metaphase
The spindle fibres pull the chromosomes by their centromeres onto the equatorial plate of the spindle so they are lined up along the middle of the cell
Describe what happens in anaphase
The centromere divides and the spindle fibres shorten and contract so the chromatids get pulled apart to the opposite poles of the cell by the spindle fibres
Describe what happens in telophase?
Nuclear membrane reforms around both groups of chromosomes which decondence to chromatin. Nucleolus reforms in each nucleus
Spindle fibres break down
What is cytokinesis?
The division of the cytoplasm
How does cytokinesis occur in animal cells?
Cleavage furrow in the middle of the cell forms. Contraction of furrow causes it to deepen until the cell membrane meets in the middle. The cells becomes completely pinched off and two cells are formed. As this happens organelles are separated.
What is a cleavage furrow?
A pinch
How does cytokinesis occur in plant cells?
Vesicles from the Golgi apparatus line up along the cell plate and secrete calcium pectate to form the middle lamella. Vesicles then secrete microfibrils of cellulose onto the middle lamella to form primary cell wall. More layers added perpendicular to the primary cell wall to form secondary cell wall. All contains lignin
What are clones?
Cells which are genetically identical to each other
How are clones made in mitosis?
Chromosomes replicated in the synthesis phase.
When chromosomes separate, one copy of the chromatid is in each of the daughter cells.
Cytoplasm divides in cytokinesis with an exact copy of the original nucleus.
What is the purpose of mitosis?
Growth and repair of tissues
In what tissues can you see mitosis?
Tissues which are actively growing like epithelial tissue in mammals like the skin and in the meristems of plants and cambium within vascular bundles
What are meristems?
A group of plant cells which divide by mitosis
What are primary meristems?
Meristems found at roots and shoots
What are secondary meristems?
Meristems which develop in woody plants
What stains are used to observe root tip cells?
Toluidine blue or orcein
Why is orcein used more commonly despite being more hazardous?
Because it produces a higher definition of chromosome structure
How can you reduce the hazard of a stain?
Putting a small amount + bottle should be fully stoppered and on a solid surface
Why do you heat the roots in hydrochloric acid?
Increase permeability of the cell so the stain penetrates more easily. Also breaks down cell wall so that the tissue is easier to spread
Why do you squash the root tip with a cover slip?
To spread the cells out so only a single layer can be seen under the microscope so the individual cells are easier to see.
Why are the root tips washed with water after being in the acid?
To wash off the acid
What is maceration?
To soften by soaking in a liquid
What is a locus?
The place on the chromosome where genes occur
Explain how you would make up a temporary slide for the mitosis root tip practical
Grow roots. Heat HCl in water bath. Add root tips and heat with HCl. Take out root tips and rinse with water. Heat with acetic orcein. Spread onto slide and press with coverslip.
Why can no visible chromosomes be seen in G1?
Chromatin results in the diffuse staining on the nucleus
Why are the stain and the root tip heated together?
So that the stain can bind with the chromosomes of the root tip
Why is the vial with the stain in it stoppered?
To stop the stain from evaporating
How many daughter cells are produced in meiosis?
Four
How many daughter cells are produced in mitosis?
Two
Are the daughter cells from meiosis haploid or diploid?
Haploid
Are the daughter cells from mitosis haploid or diploid?
Diploid
Where does meiosis occur?
Gonads
What are the gonads?
Ovaries and testes
What does haploid mean?
When a cell contains only one chromosome of a homologous pair of chromosomes
What is a bivalent?
A homologous pair of chromosomes
Why is mitosis needed in roots?
For growth to replace dead cell
For repair to fix damaged cells
Why does DNA need to be doubled during interphase?
Doubles by replication
Later be halved
Each cell gets same amount as DNA
from cytokinesis
