topic 1.6- cell division Flashcards
define mitosis
the division of the nucleus into two genetically identical daughter nuclei
what must happen before mitosis can occur?
all of the DNA in the nucleus must be replicated
when is the DNA in the nucleus replicated
during interphase
what is interphase
the period before mitosis
what happens during interphase?
each chromosome is converted from a single DNA molecule into two identical DNA molecules (chromatids)
what are the functions of mitosis?
- embryonic development
- growth
- tissue repair
- asexual reproduction
state the 4 phases of mitosis
- prophase
- metaphase
- anaphase
- telophase
mitosis is a ——– process
continuous
interphase is a…
very active phase in the life of the cell when many metabolic reactions occur
what only occurs during interphase?
DNA replication in the nucleus and protein synthesis in the cytoplasm
why does the no of mitochondria/chloroplasts in the cytoplasm increase during interphase?
due to the growth and division of these organelles
what do plants also do during interphase?
they synthesise cellulose and use vesicles to add it to their cell walls
what 3 phases does interphase consist of?
- G1 phase
- S phase
- G2 phase
G1 phase
cell grows physically larger and copies organelles/cellular components except the chromosomes
S phase
cell replicates all genetic material in its nucleus
G2 phase
cell grows more, makes proteins and organelles, and begins to reorganize its contents in preparation for mitosis
what happens to cells that are never going to divide?
they enter a phase called G0
how do chromosomes condense
by supercoiling during mitosis
what makes up each chromosome during mitosis?
a chromatid
how does condensation occur for chromosomes?
by repeatedly coiling the DNA molecule to make the chromosome shorter and wider
what is involved in supercoiling?
histones (proteins) associated with DNA and enzymes
prophase
- chromosomes become shorter and fatter by supercoiling
- nucleolus breaks down
- microtubules grow from MTOCs to form spindle-shaped array that links poles of the cell
- end; nuclear membrane breaks down
function of the nucleolus
area inside the nucleus of a cell that is made up of RNA and proteins and is where ribosomes are made.
metaphase
- microtubules continue to grow and attach to the centromeres on each chromosome
- microtubules put under tension to test whether attachment is correct (by shortening of the microtubules at the centromere)
- attachment=correct, microtubules remain on equator of cell
what allows the chromatids of a chromosome to attach to microtubules?
the two attachment points on opposite sides of each centromere
anaphase
- each centromere divides, allowing the pairs of sister chromatids to separate
- spindle microtubules pull them rapidly towards the poles of the cell
telophase
- at each pole the chromosomes are pulled into a tight group by the MTOC and a nuclear membrane reforms around them
- chromosomes uncoil and nucleolus is formed
telomere
structures found at the ends of chromosomes. They cap and protect the end of a chromosome
centromere
links a pair of sister chromatids together during cell division.
equation for mitotic index
no of cells in mitosis/total no of cells
MTOC
microtubule-organizing center; a structure found in eukaryotic cells from which microtubules emerge.
when does cytokinesis occur
after mitosis
what is cytokinesis
process of cell division
describe cytokinesis in plants
- vesicles are moved to the equator, where they fuse to form tubular structures
- these merge into two layers of membrane across the whole of the equator
how are cell walls formed after mitosis?
- pectins and other substances brought by vesicles and deposited by exocytosis between the two new membranes, forming the middle lamella that links new cell walls.
- both dcs then bring cellulose to the equator and deposit it adjacent to the middle lamella via exocytosis. this forms a cell wall adjacent to the equator
describe cytokinesis in animal cells
- cleavage furrow formed (plasma membrane pulled inwards around equator).
- this is accomplished by using a ring of contractile protein (actin and myosin) - when cleavage furrow reaches centre, the cell is pinched apart into 2 cells
what are cyclins involved in?
the control of the cell cycle
description/functions of cyclins
proteins:
- control the cell cycle and ensure that cells divide only when new cells are needed
how do cyclins work
- bind to enzymes called cyclin-dependent kinases, causing them to become active and attach phosphate groups to other proteins in the cell
- this triggers the other proteins to become active and carry out tasks specific to one of the cell cycle phases
cyclin D
triggers cells to move from G0 to G1 and from G1 to S
cyclin E
prepares cell for DNA replication in the S phase
cyclin A
actives DNA replication inside the nucleus in the S phase
cyclin B
promotes the assembly of the mitotic spindle and other tasks in the cytoplasm to prepare for mitosis
when will cyclin levels peak
when their target protein is required for function
state three things involved in the formation of primary and secondary tumours
- mutagens
- oncogenes
- metastasis
what are tumours
abnormal groups of cells that develop at any stage of life in any part of the body
when are tumours benign
when the cells adhere to each other and do not invade nearby tissues or move to other parts of the body
when are tumours malignant
when the cells become detached and move elsewhere in the body and develop secondary tutors
what are cancers?
diseases due to malignant tumours
what are carcinomas
malignant tumours
define a mutagen
an agent that changes the genetic material of an organism (either acts on the DNA or the replicative machinery)
describe the 3 types of mutagens
- Physical – Sources of radiation including X-rays (ionising), ultraviolet (UV) light and radioactive decay
- Chemical – DNA interacting substances including reactive oxygen species (ROS) and metals (e.g. arsenic)
- Biological – Viruses, certain bacteria and mobile genetic elements (transposons)
what are carcinogens
Mutagens that lead to the formation of cancer
define a mutation
random changes to the base sequences of genes
most genes ——- if they mutate
do not cause cancer
what are oncogenes
genes that become cancer-causing after mutating
why are oncogenes cancer-causing
in a normal cell, oncogenes are involved in the control of the cell cycle and cell division, so mutations in them will result in uncontrolled cell division = tumour formation
metastasis
the movement of cells from a primary tumour to set up secondary tumours in other parts of the body
smoking and cancer
there is a positive correlation between smoking and incidence of cancer;
- cancer of mouth, pharynx, larynx and lungs
- esophagus, stomach, kidney, bladder, pancreas cervix
- Cigarette smoke contains over 4,000 chemical compounds, over 60 of which are known to be carcinogenic
