3.2.2 all cells arise from other cells Flashcards
3.2.2 all cells arise from other cells
what is DNA coiled around
histones
what do histones do
they support the structure
DNA is in the form of what
a double helix
what is nuclear genetic material termed as
chromatin
describe the structure of a sister chromasome
http://www.macroevolution.net/sister-chromatids.html
before replication chromasones are always found in matching pairs , one from the mother and one from the father . what are they called ?
homologous pairs
what is the diploid number in humans
46 (2n)
what is the haploid number in humans
23 (n)
does every spesics have the same diploid number
no
peas (16)
fogs (26)
chicken (78)
what type of cells has a haploid number
gamates
when DNA is not destinguishable as individual chromosomes it is called
chromatin
what is the general length of chromosomes
0.25 to 50 micro meters
what does n represent in haploid and diploid number
it represents the amount of pairs of homologous pairs
are all cells formed by division of existing cells ?
yes
what is the definition of mitosis
Mitosis: division into two daughter cells that are genetically identical to each other and to the parent cell.
what is the definition of meiosis
Meiosis: division into four unique daughter cells with half the chromosomes of the parent cell. Genetically different. Produces the sex cells
what is the significance of mitosis
Biosynthesis- is the process by which living things use chemical reactions to create products useful for cellular metabolism
repaire tissue
asexual reproduction
The genetic stability of a multicellular organism is reliant on an accurate DNA replication system and success at various levels of DNA repair systems in the cells
what are the advantages of a-sexual reproduction
All adapted to a stable environment, rapid repopulation / populate
what are the disadvantages of a-sexual reproduction
Less able to adapt to environmental change, vulnerable to disease
the cell cycle involves 3 phases what are they
interphase
meitosis
cytokienesis
interphases has 3 stages what are they
G1 , S , G2
what happens in G1
g1 phase, also called the first gap phase, the cell grows physically larger, copies organelles, and makes the molecular building blocks it will need in later steps. (growth of cytoplasm and organelles)
what happens during S phase
synthasis of DNA
S phase. In S phase, the cell synthesizes a complete copy of the DNA in its nucleus. It also duplicates a microtubule-organizing structure called the centrosome. The centrosomes help separate DNA during M phase.
what happens during g2 phase
g phase, the cell grows more, makes proteins and organelles, and begins to reorganize its contents in preparation for mitosis. G
phase ends when mitosis begins.
it requires a lot of energy due to the increase in size and activity , but also a lot more enzymes now
what is g0 phase
this is the pahse in which many non dividing cells enter e.g brains cells or nerve cells)
in which stage are proteins made for DNA synthasis
during interpahse
what are the four main processes that take place during interpahse
- synthasis of DNA
- synthasis of ATP
- synthasis of protein
- replication of organelles
what are the four phases of mitosis
prophase
meteaphase
anaphase
telophase
what happens in prophase
nuclear envelope disapears near the end of propahse
chromatin condens to make chromasomes
seperation of centromeres
formation of miotic spindal fibers
centrioles divide and migrate to opposite poles
Plant cells lack centrioles but do develop spindle fibres therefore centrioles not essential for spindle fibre formation
what happens during metaphase
The nuclear membrane has disappeared.
the chromosomes align upon a theoretical line known as the metaphase plate. The centrosomes arer on opposite ends of the cell.
At this stage, the cell will check that all the chromosomes are aligned along the metaphase plate, with their kinetochores correctly attached. This helps to ensure sister chromatids are split evenly between the two daughter cells. An error in chromosomal alignment or spindle attachment will result in the cell halting further progress until the problem is fixed.
Spindle fibres attach to centromeres holding the pairs of sister chromatids together
https://teachmephysiology.com/biochemistry/cell-growth-death/mitosis/
what happens during anaphase
The centromeres divide separating the sister chromatids
The spindle fibres contract pulling the sister chromatids apart to opposite poles.
Centromere moves first making the chromatids appear v-shaped
Spindle fibres not attached to chromatids will elongate the cell to prepare it for division.
what happens during telophase
The chromatids have arrived at the poles and are now called chromosomes.
They become long and thin once more
A nuclear envelope reforms around each set.
In this phase, the cell has elongated and is nearly finished dividing. Cell-like features begin to reappear such as the reformation of two nuclei (one for each cell). The chromosomes then de-condense and the mitotic spindle fibres are broken down.
what happens during cytokeinsis
The third phase in the cell cycle
It is the physical process of cell division
Parental cell cytoplasm divides
Production of two daughter cells
microfiliments pull in cell surface membrane drawing it inwards ( givinf a pinching effect)
how do plant cells under go cyokeinesis
Golgi vesicles carrying
materials to make a
Cell wall accumulate in
the centre region of the
cell.
The Golgi vesicles fuse
and form a CELL PLATE.
Inside the vesicles a
middle lamella forms with
cellulose either side of it.
Two new separate cells
are formed
state two diffrences in plant and animal mitosis
animal cells :
centrioles act as a focous for spindal fibers which form arcs
cytokiensis is by microfilliments (pinch)
plant cells :
no centrioles , no spindal fibers , fibers are parrallel than curved
cytokeinesis is by cell plates formation , as golgi vesicles secreate new cell wall
cancer is causes by what ?
- mutagens
- enviroment e.g sun
- error in copying DNA
how would you measure if a tissue is cancerous or not ?
mitotic index
number of cells with visibal chromasomes/total number of cells
infocard (read and recite)
An interphase cell in the g0 phase is not preparing for division, but is instead performing all of the other functions appropriate for that particular cell type. some mature cells such as skeletal muscle cells and most neurones remain in g0 indefinitely and never divide. in contrast , stem cells which divide repeatedly with very brief interphase periods, never enter g0
infocard (read and recite)
G1 (8 or more hours)
ac ell that is ready to divide first enters the G1 phase in this phase the cell makes enoughmitochondria, cytoskeletal elements , endoplasmic reticula , ribosomes , golgi membranes , and cytosol for two functional cells , centriole replication begins in G1 and commonly continues until G2 . in cells dividing at top speed , G1 may last just 8-12 hrs such cells pour all their energy into mitosis and all other activies cease if G1 lasts for days weeks or months preparation for mitosis occurs as the cells perform their normal functions
infocard (read and recite)
S phase (lasts between 6 to 8 hrs)
when the activities of the G1 phase have been compleasted the cell enters the S phase over the next 6-8 hours the cell deuplicates its chromosomes . this involves DNA replication and the synthesis of histones and other proteins in the nucleus
infocard (read and recite)
G2 (last for around 2 to 5 hrs)
once DNA replication has ended there is a brief (2-5 hr) G2 phase devoted to last-min protein synthesis and to the completion of centrioles replication.
what causes cancer
a mutation in a gene which controls the cell cycle causing damage to the gene leading to the develpment of a tumour.
cancer is most common in lungs , prostate gland , breasts , ovaries , stomach , oesophgus and pancreas
read this artical
https://teachmephysiology.com/biochemistry/cell-growth-death/mitosis/
what is a benign tumour
Benign Tumours – tumours that do not spread from their point of origin but they may still be painful because they compress surrounding tissues and displace them. Benign tumours are usually encased in a fibrous capsule and do not invade the tissue in which they originate. Do not cause cancer and do not metastasise
what is a malignant tumours
Malignant Tumours – divide in a more uncontrolled way than benign tumours and can be carried by the blood stream or lymphatic system to invade other tissues, causing secondary cancers. This process is called metastasis.
what is a tumour
Tumour – A mass of abnormal cells that have developed by uncontrolled cell division
how do malignant tumours cause secondary tumours
- mechanisms controlling cell division breaks down
2 . primary tumour formed by repeated division of affected cell - cancerous cells escapes to blood or lymph
- cancerous cell carried to diffrent tissue
- secondary tumour (metastasis ) formed anywhere in the body
metastasis - the development of secondary malignant growths at a distance from a primary site of cancer.
what are the two families that controll the cell cycle
tumer-supressor gene
proto-oncogene
how does a proto oncogene work and become oncognee
A proto-oncogene is a gene that encodes a protein that is involved in regulation of cell growth or proliferation
Can be mutated into a cancer promoting oncogene where the gene is stuck in a state of constant activity
Uncontrolled growth leading to tumour development
it is responsible for the ‘gas’ for the cell cycle
how does a tumour suppressor gene work and how does a mutation cause cancer
Tumour suppressor genes encode proteins that inhibit cell proliferation.
Loss of these genes can contribute to the development of cancer
what is prolification
reproduction involving a cell growing directly from an older one.
what are the three ways to treat cancer
Surgery-removal of the tumour
Radiotherapy-radiation damages the DNA and causes cells to kill them selves
Chemotherapy- drugs are used to kill cancerous cells preventing them from dividing or damaging them so they kill themselves.
what are the two types of chemotherapy
- Prevent the DNA from replicating
Some drugs target G1 region in interphase
Prevent the synthesis of enzymes needed for DNA replication and therefore cell is unable to enter S phase
Some drugs target the S phase
Includes radiation as DNA becomes so damaged cell will kill itself (checkpoints)
2.Inhibit the metaphase stage of mitosis by interfering with spindle formation
describe the process of cell divition in prokaryotes
By Binary Fission
A sexual reproduction in unicellular organisms in which a single cell divides to form two identical daughter cells
Very similar to mitosis genetic material is replicated before the prokaryote splits Into two.
Replicated large loop of DNA attaches to cytoplasmic membrane. As cell grows the DNA is separated
The main DNA loop is only replicated once, but plasmids can be replicated numerous times
Daughter cells can contain variable numbers of plasmids
how do viral virasis replicate
Attachment: The virus attaches to a host cell. In the case of the bacteriophage it will attach to a bacterium.
Entry: The virus forms a hole in the membrane or cell wall of the host. The nucleic acid of the virus enters the host cell.
Synthesis: The virus’ nucleic acid is used to make new viral nucleic acid and proteins for the new viruses being produced. (The host cells’ DNA becomes deactivated)
Assembly: New viruses are made inside the host cell.
Release: The host cell bursts to release the new viruses. The bursting is called lysis.
what is meristems
Meristems are regions of plant cells that are actively dividing by mitosis. They are small unspecialised cells forming a tissue called Meristematic tissue.
Meristematic tissue is found in growing regions of root tips, stem tips and in the cambium which is involved in thickening growth (between xylem and phloem tissue).
