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Summary Cells and Viruses
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Detailed notes following from the Biology B Edexcel textbook with the specification points and notes underneath - A level course
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TOPIC 2Eukaryoti c and prokaryoti c cell structure and functi on
i Understand that cell theory is a unifying concept that states that cells are a fundamental unit of
structure, function and organisation in all living organisms.
Modern cell theory states
1. All living things are composed of one or more cells
2. The cell is the basic unit of life
3. New cells arise from pre-existing cells
ii Understand that in complex organisms, cells are organised into tissues, organs, and organ systems.
iii Know the ultrastructure of prokaryotic cells and the structure of organelles, including: nucleoid,
plasmids, 70S ribosomes and cell wall.
Prokaryotes have a nucleoid – genetic material
packaged in on a single circular piece of DNA
forming BACTERIAL CHROMOSOME but there
is no NUCLEAR MEMBRANE
Bacterial cell wall is a mesh work of tough
protein called peptidoglycan and can be
gram positive or gram negative:
Peptidoglycan – many parallel
polysaccharide chains with short
peptide cross-linkages forming a big net
structure
Plasmids – separate circles of DNA with extrachromosomal genes
found in cytoplasm that only carry a few genes; can be shared during sexual reproduction using pili
, (appendages from surface of bacteria allowing prokaryote to stick to surfaces) and often have genes
coding for antibiotic resistance
70S ribosomes – site of protein synthesis; not attached to any membranes and are smaller than
those in eukaryotic cells
iv Be able to distinguish between Gram positive and Gram negative bacterial cell walls and
understand why each type reacts differently to some antibiotics.
Gram positive bacteria have
THICK cell walls made almost
entirely of PEPTIDOGLYCAN.
Become purple when
stained by crystal violet
Gram negative bacteria
have THIN cell walls of
peptidoglycan and an
addition OUTER membrane
with high LIPID content that
prevents crystal violet stain
getting to cell wall, so cells do not become purple (add safarin that stains red)
Gram negative bacteria are normally more resistant to antibiotics as they have a largely
impermeable cell wall.
v Know the ultrastructure of eukaryotic cells and the functions of organelles, including: nucleus,
nucleolus, 80S ribosomes, rough and smooth endoplasmic reticulum, mitochondria, centrioles,
lysosomes, Golgi apparatus, cell wall, chloroplasts, vacuole and tonoplast.
Nucleus – acts as control centre of cell through
production of mRNA and tRNA and hence protein
synthesis; retain genetic material of cell in form of DNA
and chromosomes; manufacture ribosomal RNA and
assemble ribosomes
Nucleolus – area of dense chromatin within nucleus;
granular structure and not membrane bound; makes
ribosomal RNA and assembles ribosomes
Endoplasmic reticulum
Rough ER: provide large SA for synthesis of proteins and
glycoproteins; provide pathway for transport of
material eg proteins
Smooth ER: synthesise, store and transport lipids and
carbs; metabolise carbs; aid in detox of drugs
Golgi apparatus
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