The voice of the Genome - unit 2 biology Edexcel

voice of genome - only organelles 

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The voice of the Genome ­ Chapter 3.1 Animal
cells and asexual reproduction
I can distinguish between Eukaryotic and prokaryotic cells in terms of their structure and ultrastructure:
Living organisms are made up of cells, most of them being familiar cells ­ animals, plants, protoctists and many fungi
have cells that contain membrane-bounded organelles such as the nucleus, mitochondria and chloroplast; these
organisms are known as eukaryotes, made up of eukaryotic cells.
Other organisms, ancient in terms of biology, like blue or green algae have cells of a very different type:
prokaryotes. Prokaryotic cells lack much structure or organisation: they do not have a membrane bound nucleus ­ the
genetic material is a single strand coiled up in
the centre to form the nucleoid, sometimes
there are extra pieces of genetic material
fragmented through the cell called plasmids.
The cytoplasm contains enzymes, ribosomes
and food-storage granules but lacks other
features such as the Golgi apparatus,
endoplasmic reticulum, mitochondria and
chloroplasts. Respiration therefore takes place
on a special piece of the membrane called a
mesosome and those prokaryotes that can
photosynthesise have a form of chlorophyll
but no chloroplasts to hold it.
Prokaryotic Cells Eukaryotic cells
small cells (< 5 mm) larger cells (> 10 mm)
always unicellular often multicellular
no nucleus or any membrane-bound organelles, such as always have nucleus and other membrane-bound
mitochondria organelles
DNA is circular, without proteins DNA is linear and associated with proteins to form
ribosomes are small (70S) ribosomes are large (80S)
no cytoskeleton always has a cytoskeleton
motility by rigid rotating flagellum made of flagellin motility by flexible waving undulipodium, made of tubulin
cell division is by binary fission cell division is by mitosis or meiosis
reproduction is always asexual reproduction is asexual or sexual
huge variety of metabolic pathways common metabolic pathways
I can describe the ultrastructure of an animal cell (eukaryotic) and recognise these organelles from EM(electron
microscope) images:
A typical animal cell is surrounded by a cell membrane; inside that membrane is a jelly like liquid called the cytoplasm,
containing a nucleus ­ the two known together as the protoplasm. The cytoplasm contains what is needed for the
functions of the cell whilst the nucleus is vital to the survival of the cell.
Membranes are important in a cell as an outer boundary, controlling what comes in and out of the cell. As well as the
initial outer-membrane of the cell, there are also intercellular membranes which are vital to the workings of the cell.
The nucleus ­ usually the largest organelle in the cell (10-20m)and can be seen with the light microscope. Electron
microscopes portray how the nucleus, which is normally spherical, is surrounded by a double nuclear membrane
containing nuclear pores. Chemicals pass in and out of these pores so that it can control the events in the cytoplasm.
The nuclear envelope (membrane) is two main substances: nucleic acids and proteins. Acids are (DNA and RNA). When
the DNA is not dividing, the DNA is bonded to the protein to form chromatin, which looks like tiny granules. The

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­ an extra dense area of almost pure DNA and protein. The nucleolus is
involved in the production of ribosomes, cell growth and division.
Lysosome ­ the function of these organelles are to break down any of the organelles that have been worn out. They
appear as dark, spherical bodies in the cytoplasm containing many digestive enzymes. They frequently fuse with each
other and with a membrane bound vacuole containing either food or a foreign organelle.…read more

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Simplified table:
Organelle Description (structure) Function
Nucleus A large organelle surrounded by a nuclear Chromatin is made from proteins and DNA.
envelope (double membrane) which contains The pores allow substances (like RNA) to move
many pores. The nucleus contains chromatin and between the nucleus and cytoplasm.…read more

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The lungs - example of an animal organ, made up of the following tissues
1. Squamous epithelial tissue ­ surrounds the alveoli (gaseous exchange occurrence)
2. Fibrous connective tissue ­ helps force air back out of the lungs when exhaling
3. Blood vessels ­ capillaries surround the alveoli
Organs are organised into Systems:
Organs work together to form organ systems ­ each system has a particular function:
The respiratory system is made up of all the organs, tissues and cells involved in breathing.…read more

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Prophase ­ The chromosomes condense, getting shorter and fatter. The centrioles start moving to opposite ends of
the cell, forming a network of protein fibres across it called the spindle. The nuclear envelope breaks down and
chromosomes lie free in the cytoplasm. As mitosis begins, the chromosomes are made of two strands joined in the
middle by a centromere. The separate strands are called chromatids. These are two strands because each
chromosome has already made an identical copy of itself during interphase.…read more

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Telophase ­ The chromatids reach the opposite poles on the spindle. They uncoil and become long and thin again.
They're now called chromosomes again. A nuclear envelope forms around each group of chromosomes so now there
are two nuclei and centrioles reform.
Cytokinesis - The cytoplasm divides and there are now two daughter cells that are genetically identical to the
original cell and to each other.…read more


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