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Summary Cell Structure Revision Notes
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Detailed revision notes on cell structure and microscopy for Module 2.1 from the OCR A level biology course.
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CELL STRUCTUREEUKARYOTIC CELLS
Animal, plant, fungal & protoctist cells are all eukaryotic cells because they have:
a nucleus surrounded by a nuclear envelope & contain DNA organised &
wound into linear chromosomes
a nucleolus containing RNA, ribosomes are made & chromosomes. unwind to
form chromatin
cytoplasm
cytoskeleton
plasma membrane
membrane bound organelles
small vesicles
ribosomes
NUCLEUS
Nearly all cells have a nucleus
usually the largest cell organelle.
takes in stains more than the cytoplasm so looks darker
surrounded by 2 membranes with a small gap between them - nuclear
envelope
within the envelope there are protein complexes called nuclear pores
o provide channels in the membrane
contains DNA + the template for making RNA
DNA CAN BE IN ONE OF 2 FORMS
O coiled, condensed to form chromosomes as in cell division.
O chromatin, a tangle of DNA & proteins – histones
NUCLEOLUS
very darkly stained area in the nucleus
contains DNA that is being used to make ribosomes
NUCLEOPLASM
nuclear sap
gel like
denser than cytoplasm
contains proteins, nucleotides & ions
NUCLEAR MEMBRANE
doubled layer
similar structure as cell membrane.
continuous with endoplasmic reticulum
with microscopic pores for exchange of materials between nucleus &
cytoplasm
, ENDOMEMBRANES - ROUGH ENDOPLASMIC RETICULUM
network of folded, internal membranes
cisternae - the enclosed flattened membranes-bounded sacs
o includes: rough endoplasmic reticulum, smooth endoplasmic reticulum
& the Golgi apparatus
o all involved in processing, transport & export
rough endoplasmic reticulum (RER) - endoplasmic reticulum combined with
ribosomes
RER usually continuous with the nuclear envelope & is where most protein.
synthesis takes place
as the protein molecules are made, & combined with carbohydrates, they
collect inside the cisternae (the lumen) & can be transported to other areas of
the cell e.g. GA for further processing
cells that produce a lot of protein have extra RER
SMOOTH ENDOPLASMIC RETICULUM (SER)
continuous with the RER but doesn't have ribosomes
makes lipids including phospholipids
also contains enzymes that are known to detoxify lipid-soluble drugs & some
harmful products of metabolism
GOLGI APPARATUS
usually located near the nucleus
consists of stacks of flattened membrane bounded sacs – cisternae
not interconnected
constantly changing
o at one end of the stacks new cisternae are constantly formed by fusion
of vesicles pinched from the ER
o at the other end, small Golgi vesicles are pinched off constantly
vesicles contain proteins & lipids made in the ER
o to be modified, prepared for secretion, then delivered to the cell
membrane
also responsible for making lysosomes & the synthesis of cell wall materials
in plants
Discovered by Camillo Golgi who noticed that a certain stain selectively
marked only some internal ribosomes
MITOCHONDRIA
found in both plant & animal cells
surrounded by on envelope of 2 membranes
o inner folded to form cristae
site of aerobic respiration in a cell
ATP is made on the cristae during the process of oxidative phosphorylation
background material of the mitochondrion is called the matrix & is the site of
the Krebs cycle
contain their own DNA & 70s ribosomes
rich in cells which require a large amount of energy e.g., sperm/muscle cells
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