Summary Cell Structure Revision Notes

CELL STRUCTURE
EUKARYOTIC 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