OCR AS Biology F211 Cells Notes

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New Cells - parent and daughter cells

Two nuclei from one

Cell cycles and life cycles are not all the same

Cell Specialisation

Organising the organism 

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Hold the instructions for making new cells
The daughter cells produced during the cell cycle must contain a copy of all these instructions, so they must contain a
FULL SET of chromosomes, copied exactly from the chromosomes in the parent cell.
They are in the nucleus of the eukaryotic cells. Each chromosome contains one molecule of DNA, which includes
specific lengths of DNA called genes
In humans there are 46 chromosomes in the nucleus of each cell
Copying and separating
In eukaryotes, the molecules of DNA that make up each chromosome are wrapped around proteins called
The DNA and the histone proteins together are called CHROMATIN.
Before a cell can divide to produce two new daughter cells, the DNA of each chromosome much be replicated.
Two replicas are produced. Each is an exact copy of the original; they remain held together at a point called a
This plays an important role in the process of nuclear division.
Checks and balances
As chromosomes are being replicated, proof-reading enzymes move along the new DNA strands and check that the
copying has been done properly.
If genes are not copied precisely, the resulting mutations may mean the new cells fail to function.
How fast is the cycle
The length of time taken for a parent cell to divide into two daughter cells, and for each to grow to full size, varies
between species and cell type
Prokaryotic ­ 30 mins
Single cells eukaryotic organisms - 4 hours
The cell cycle is divided into stages
Interphase ­ DNA replicates in this stage
Mitosis ­ the nucleus divides and chromatids separate
Cytokinesis ­ the cytoplasm divides or cleaves
Growth phases ­ each new cell grows to full size
Mitosis occupies only a small proportion of the cell cycle and the remaining larger portion includes copying and
checking genetic information on the DNA and processes associated with growth.
What is so important about making new cells?
All organisms need to produce genetically identical daughter cells
Asexual reproduction ­ single-celled organisms divide to produce TWO DAUGHTER CELLS that are separate
Growth ­ multicellular organisms grow by producing extra cells. Each new cell is GENETICALLY IDENTICAL to the
parent cells and so can perform the same functions.
Repair ­ damaged cells need to be replaced by new ones that perform the same functions and so need to be identical
Replacement ­ red blood cells and skin cells are replaced by new ones.
Mitosis in four stages
Mitosis refers to the process of nuclear division where TWO GENETICALLY IDENTICAL NUCLEI are formed from
one parent cell nucleus
Four stages -PMAT

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Prophase ­ replicated chromosomes supercoil (shorten and thicken), chromosomes already replicated in interphase.
They consist of a pair of sister chromatids. Centriole divided in 2 and they move to opposite ends of cell to form
spindle fibres.
Metaphase ­ replicated chromosomes line up, down the middle of the cell and each becomes attached to a spindle
thread by its centromere
Anaphase ­ the replicas of each chromosome are pulled apart from each other towards opposite poles of the cell.…read more

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In animal cells cytokinesis starts from the outside ­ nipping in the cell membrane and cytoplasm along what is termed
a cleavage furrow.
In plant cells, cytokinesis starts with the formation of a cell plate where the spindle equator was.
The cell then lays down new membrane and cell wall material along this plate.
The cell plant is not a solid structure, but a single plan along which the new cell wall forms.…read more

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Both are human cells and each began with the same set of chromosomes, so each is potentially capable of carrying
out the same functions.
All blood cells are produced from undifferentiated stem cells in the bone marrow
The cells destined to become erythrocytes lose their nucleus, mitochondria, Golgi body and rough endoplasmic
They are packed full of the protein haemoglobin.
The shape of the cells change so that they become biconcave discs and they are then capable of transporting oxygen
from lungs to tissues.…read more

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Ciliated epithelial tissue ­ made up of column shaped cells. Often found on the inner surface of the tubes, e.g. trachea.
The part of the cell surface that is exposed in the tube space (lumen) is covered with tiny projections called cilia. Cilia
wave in a synchronized rhythm and move the mucus.
In the breathing tract, small particles and microorganisms are trapped in the mucus.
Cilia become damaged by tar in smoke and are destroyed.…read more


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