Cell Cycle and Cell Division Flashcards
What is a chromosome? (1)
Independent DNA molecule in a condensed form which contains many genes (using histones)
What is a gene? (1)
Section of DNA coding for a specific polypeptide
What is the cell cycle? (2)
The regular sequence of growth and division that cells undergo
What are the stages of the cell cycle? (3)
Interphase
Mitosis or meiosis
Cytokinesis
What happens during interphase? (3)
G1: cell increases in size and new proteins are made
S: DNA replicates by semi-conservative replication
G2: Cell gets ready for division, synthesises and stores of ATP and new organelles synthesised
What is the purpose of mitosis? (5)
Produces 2 identical daughter cells for:
Repair of damaged tissues
Replacement of worn out/dead cells
Increasing cell number and growth of an organism
Asexual reproduction
What are the stages of mitosis? (4)
P M A T
P - prophase
M- metaphase
A - anaphase
T - telophase
What happens during prophase? (4)
Chromosomes supercoil and condense to become visible
Nuclear membrane starts to break down (chromosome free in cytoplasm)
Centrioles move to opposite poles and make mitotic spindle fibres
Each chromosome appears as 2 identical sister chromatids joined at the centromere (X-shaped)
What happens during metaphase? (2)
Sister chromatids line up along the equator
And attached to spindle fibres by their centromere
What happens during anaphase? (3)
Spindle fibres contract
Centromere splits
Identical sister chromatids pulled to opposite poles and appear as 2 distinct chromosomes (āVā shape)
What happens during telophase? (2)
Nuclear membrane starts to reform around each set of chromosomes
Chromosomes unwind and become thinner to become invisible again
What happens during cytokinesis? (2)
Cytoplasm splits
2 identical daughter cells formed
What are homologous chromosomes? (2)
Chromosomes that have the same genes in the same gene loci but may have different alleles of the genes
One chromosome is maternal and the other is paternal
What is meiosis? (2)
Type of cell division that results in four genetically different daughter cells each with half the number of chromosomes of the parent cell
What happens during the first stage of meiosis? (3)
Homologous chromosomes pair to form a bivalent
Crossing over takes place at the chiasmata
Cell divides into two and homologous chromosomes separate randomly
What happens during the second stage of meiosis? (2)
Independent segregation
Each cell divides to produce 4 genetically different daughter cells
How does meiosis create genetic variation? (2)
Crossing over and independent segregation
Both result in new combination of alleles
What is crossing over? (4)
Homologous chromosomes associate (bivalent formed)
Chiasmata forms
Equal lengths of alleles exchanged between non-sister chromatids at the chiasmata
New combination of alleles
What is independent segregation? (2)
Maternal and paternal chromosomes are re-shuffled in any combination on the equator of the cell
Creates new combinations of alleles therefore increasing genetic variation
What is binary fission? (1)
A type cell division used by prokaryotic cells to reproduce & split into two
What is the process of binary fission? (4)
Replication of circular DNA and of plasmids
Cell elongates from the middle and separates the two DNA molecules, which are attached to different parts of the cell membrane
New cell wall (murein) forms down the middle of the elongated cell which eventually meets
Cell divides into 2
Why does mitosis not take place in prokaryotes? (4)
There is no nucleus, no chromatids, no centrioles and no spindle fibres
Explain the procedure of a root tip squash experiment (3)
Prepare a temporary mount of root tissue
Focus an optical microscope on the slide. Count total number of cells in the field of view and number of cells in a stage of mitosis
Calculate mitotic index (proportion of cells undergoing mitosis)
Explain how to prepare a temporary mount (7)
Place end section of root in acid to halt cell division
Wash end section of root in water
Cut tip from root section
Thin section
Put on slide in water/solution/stain
Break up the tissue with a mounted needle
Add cover slip and squash
Why is only the tip of the root used (2)
Where mitosis occurs
Cells further from the root tip are elongating rather than dividing
Why are viruses classified as non-living? (3)
No cytoplasm
No metabolism
Cannot self-replicate
Outline how viruses replicate (4)
Attachment proteins attach to receptor on host cell membrane
Enveloped viruses fuse with cell membrane OR release DNA/RNA into cytoplasm OR viruses inject DNA/RNA
Host cells use viral genetic information to synthesise new viral proteins
How do new viral particles leave the host cell (2)
Bud off and use cell membrane to form envelope
Cause lysis of host cell
Why is it difficult to develop effective treatments against viruses (2)
Replicate inside living cells so difficult to kill them without killing host cells
