Summary Biology Edexcel A full notes (SNAB) topics 1-8

TOPIC 3

CELL STRUCTURE

PROKARYOTE EUKARYOTE
No nuclei or other membrane bound organelles Contain membrane bound organelles
Extremely small; diameter between 0.5 and 5 micrometres Larger 20+ micrometres
Circular DNA free in cytoplasm Linear DNA in nucleus
Cell wall always Not always a cell wall
 Animal cells are eukaryotic

STRUCTURE FUNCTION
Nucleus  Enclosed by double  The DNA in
memb; envelope chromosomes controls
 Envelope has pores protein synthesis
 Contains chromosomes,  Pores = substances
chromatin and nucleoli move between nucleus
and cytoplasm
 Nucleolus makes
ribosomes

Nucleolus  Dense body within the  Where ribosomes are
nucleus made




Ribosome  No membrane  Use info in nucleic acid =
 Large and small subunit site of protein synthesis
of protein and RNA
 Free in cytoplasm or
attached to ER

Chloroplast  2 membranes  Chlorophyll in grana =
 Grana in stroma – photosynthesis
stacked membranes
 Circular DNA, ribosomes
and starch grains in
stroma

Centrioles  2 small, hollow cylinders  Form spindle of protein
formed by a ring of fibres on which
microtubules chromosomes are
 Found in animal cells, separated during nuclear
but only some plant cells division
 Each cylinder = 9 fibres  Involved in transport
within cytoplasm
Vacuole  Single membrane  Stores (waste) products
 Cell sap – solution of  Volume affects turgidity
mineral salts, pigments, of cell
organic acids etc.

, Cell surface membrane/  Phospholipid bilayer  Pp barrier controls
plasma membrane  Proteins help form a pp passage of substances
barrier



Rough endoplasmic  System of fluid filled  Protein synthesis on
reticulum membrane bound ribosomes
flattened sacs =  Proteins transported
cisternae through ER – folded and
 Ribosomes attached to processed
the outer surface
Smooth endoplasmic  System of fluid filled  Makes and processes
reticulum membrane bound sacs = lipids and steroids
cisternae
 No ribosomes attached
to outer surface

Golgi apparatus  Stacks of fluid filled  Receives proteins
flattened membrane synthesised on ER
bound sacs  Modifies and packages
 Sacs formed by fusion of proteins in vesicles for
vesicles from ER transport
 Vesicles at edges of sacs  Involves added carbs =
glycoproteins
 Makes lysosomes
Mitochondrion  Double membrane  Site of (later) aerobic
 Inner membrane folded respiration
= cristae  Produces ATP
 Matrix w enzymes used  Found in large numbers
for respiration, circular in cells that are very
DNA molecule and active and require a lot
ribosomes of energy
Cell wall  Made of cellulose  Mechanical support and
microfibrils and protection
polysaccharides  Prevents cell from
bursting




Lysosome  Single membrane  Breaks down unwanted
 Spherical sacs w structures because
digestive enzymes contains digestive
enzymes
 Destroys old organelles
and cells
 Digests contents of
vacuoles formed by
phagocytosis


 Movement of proteins
1. Transcription of DNA to mRNA in nucleus
2. mRNA leaves nucleus
3. Protein made on ribosomes enter rough ER
4. Protein moves through the ER assuming 3D shape en route as they are
folded and processed
5. Vesicles pinched off the rough ER contain the protein
6. Vesicles from rough ER fuse to form the flattened sacs of the golgi
apparatus