Cell Cycle & Cell Division Flashcards
(34 cards)
Describe the features of Prophase
- Nuclear membrane begins to breakdown;
- Centrioles move to poles of the cell;
- Chromatin supercoils and condense into chromosomes around HISTONES;
- Each chomosome consists of two identical sister chromatids joined by a centromere;
Describe the features of Metaphase
- Spidle fibres form;
- Spindle fibres attach to the centromere of chromosomes;
- Chromosomes align at the equator of the cell;
Describe the features of Anaphase
- Spindle fibres shorten and centromere splits;
- Sister chromatids are separated;
- Chromatids pulled to opposite poles of the cell;
- Chromatids are in a V shape formation;
Describe the features of Telophase
- Nuclear membrane begins to reform;
- Chromosomes unwind/ uncoil / become longer.
State the stages of the cell cycle
Interphase (G1-S-G2)
Prophase
Metaphase
Anaphase
Telophase
(Cytokinesis)
In which phase of the cell cycle does DNA mass double?
S phase of Interphase
Define a chromosome
A chromosome is an independent DNA molecule which has been supercoiled into a condensed form.
Contains many genes
What is a diploid cell?
A cell that has 2n chromosomes
A somatic cell
What is a haploid cell?
A (gamete) cell that has n chromosomes.
Which cells divide by mitosis?
Stem cells (only)
Why is MITOSIS important? [3]
- Increasing cell numbers and growth of an organism
- Repair of damaged tissues (not cells)
- Replacement of worn out / dead cells
Describe the appearance and behaviour of chromosomes during mitosis: [5]
- During prophase, chromosomes supercoil and condense to become visible;
- Chromosomes appear as 2 identical sister chromatids joined by a centromere;
- During metaphase chromosomes line up on the equator of the cell;
- Chromosomes attach to the spindle fibres;
- By their centromeres;
- During anaphase, the centromere splits;
- Sister chromatids are pulled to opposite poles of the cell making a V shape;
- During telophase, chromatids uncoil and become thinner;
Define allele
Different version of the same gene
Define ‘Gene’
Section of DNA base sequences on a chromosome coding for one specific polypeptide
Define Sister chromatid
One of the two strands of a replicated chromosome that are joined together by a single centromere prior to cell division
What is a tumour? [2]
- Mass of cells/tissue OR Abnormal cells/tissue;
- Uncontrolled mitosis/ uncontrolled rapid cell division;
Describe how you would determine a reliable mitotic index (MI) from tissue observed with an optical microscope.
Do not include details of how you would prepare the tissue observed with an optical microscope. [3]
- Count cells in mitosis (visible chromosomes) in field of view;
- Divide this by total number of cells in field of view;
- Repeat many/at least 5 times
OR
- Select (fields of view) at random;
Describe and explain what the student should have done when counting cells to make sure that the mitotic index he obtained for this root tip was accurate. [2]
Description; Explanation;
E.g,
* Examine large number of fields of view / many cells;
* To ensure representative sample;
OR
* Repeat count;
* To ensure figures are correct;
OR
- Method to deal with part cells shown at edge /count only whole cells;
- To standardise counting;
Describe binary fission in bacteria. [3]
- Replication of (circular) DNA;
- Replication of plasmids;
- Division of cytoplasm (to produce 2 daughter cells);
Describe Viral replication [5]
- Attachment proteins attach to receptors
- (viral) nucleic acid enters cell
- Nucleci acid replicated in cell OR Reverse transcriptase makes DNA from RNA
- Cell produces (viral) protein/capsid/enzymes
- Virus assembled and released (from cell)
Describe how the process of meiosis results in haploid cells. Do not include descriptions of how genetic variation is produced in meiosis. [5]
- DNA replication (during late interphase);
- Two nuclear divisions;
- Separation of homologous chromosomes (in first division);
- Separation of (sister) chromatids (in second division);
- Produces 4 (haploid) cells/nuclei;
Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how. [7]
- Homologous chromosomes pair up;
- maternal and paternal chromosomes are arranged in any order;
- Independent segregation (RANDOM);
- Crossing over (RARE);
- (Equal) Portions of chromatids are swapped between chromosomes;
- Produces new combination of alleles;
- Chromatids separated at meiosis II/ later;
Describe the process of crossing over and explain how it increases genetic diversity. [4]
- Homologous pairs of chromosomes associate / form a bivalent;
- Chiasma(ta) form;
- (Equal) lengths of (non-sister) chromatids / alleles are exchanged;
- Producing new combinations of alleles;
Give two differences between mitosis and meiosis. [2]
Mitosis given first
* One division, two divisions in meiosis;
* (Daughter) cells genetically identical, daughter cells genetically different in meiosis;
* Two cells produced, (usually) four cells produced in meiosis;
* Diploid to diploid/haploid to haploid, diploid to haploid in meiosis;
* Separation of homologous chromosomes only in meiosis;
* Crossing over only in meiosis;
* Independent segregation only in meiosis;
