NOTES

• HOW DO CELLS PROVIDE INDIRECT EVIDENCE FOR EVOLUTION

  • all life on earth exists as cells
  • any differences between cells are due to additions of extra features
  • all cells have the same basic features
• DID MITOCHONDRIA AND CHLOROPLASTS EVOLVE FROM BACTERIA?

  ENDOSYMBIOTIC THEORY: large prokaryotic cells engulfed smaller photosynthetic bacteria and smaller ones that could make energy / ATP using oxygen. Instead of smaller bacteria digested, remained intact.

  • photosynthetic bacteria - evolved into chloroplasts
  • bacteria making energy using oxygen - evolved into mitochondria
• FACTS THAT SUPPORT ENDOSYMBIOTIC THEORY

  • both have own DNA like prokaryotes
  • DNA arranged like prokaryotes (loop)
  • divide on their own, like bacteria
• STRUCTURE OF EUKARYOTIC CELLS

  • complex
  • can be multi or unicellular
  • larger
  • membrane bound organelles
  • larger ribosomes - 80s
  • DNA
• EUKARYOTIC CELL DNA

  • in a membrane bound nucleus
  • wrapped tightly around histone proteins to form chromatin
  • chromatin coiled into chromosomes
  • linear DNA molecules

  
• NUCLEUS STRUCTURE

  • double membrane
  • nuclear envelope with nuclear pores
  • nucleolus
  • chromosomes (which are made from protein-bound linear DNA)
• NUCLEUS FUNCTION

  • controls activities of cell by controlling transcription of DNA
  • site of DNA replication and transcription to produce mRNA
  • instructions to make proteins
  • contains the genetic material for each cell
  • pores allow transfer of substances (RNA)
  • nucleolus makes rRNA and is where ribosome subunits assemble
• CELL SURFACE MEMBRANE STRUCTURE

  • phospholipid bilayer with molecules embedded
  • surrounds animal cells and is inside cell wall of other cells

  
• CELL SURFACE MEMBRANE FUNCTION

  • regulates movement of substances into and out of the cell
  • has receptor molecules to respond to chemicals like hormones

  
• ROUGH ENDOPLASMIC RETICULUM AND SOFT ENDOPLASMIC RETICULUM STRUCTURE

  • system / sheets of membranes enclosing a fluid filled space
  • forms flattened sacs called cisternae
  • RER covered in ribosomes on surface
• ROUGH ENDOPLASMIC RETICULUM FUNCTION

  • protein synthesis on the ribosomes
  • proteins into the lumen of RER and folds into tertiary structure
  • polypeptide packed into vesicles to travel to golgi apparatus

  
• SMOOTH ENDOPLASMIC RETICULUM FUNCTION

  • synthesis and stores lipids and carbohydrates

  
• GOLGI APPARATUS STRUCTURE

  • system of membranes enclosing a fluid filled space
  • folded to form cisternae

  
• GOLGI APPARATUS FUNCTION

  • processes and modifies proteins / polypeptide chain
  • packs it into vesicles
  • makes vesicles and lysosomes

  
• GOLGI VESICLES STRUCTURE

  • small, fluid filled, membrane bound sac
  • found at edges of apparatus

  
• GOLGI VESICLES FUNCTION

  • transports lipids and proteins made by the Golgi apparatus
  • to the cell surface membrane where it fuses with the membrane
  • releases contents out of the cell by exocytosis

  
• LYSOSOMES STRUCTURE

  • bags of powerful digestive lysosomal enzymes (hydrolytic enzymes)
  • membrane bound sac with no clear internal structure which is acid filled

  
• LYSOSOMES FUNCTION

  • digest large molecules into smaller / soluble molecules
  • key role in phagocytosis
  • digest old / worn out organelles in the cell
  • digest invading cells
  • transfer enzymes out of the cell by exocytosis

  
• RIBOSOMES STRUCTURE

  • made up of 2 subunits
  • made of proteins and RNA
  • either floats free in cytoplasm or attached to the surface of the RER

  
• RIBOSOMES FUNCTION

  • site of protein synthesis - translation
  • proteins made by ribosomes in cytoplasm remain in cytoplasm
  • ones made on RER are secreted from the cell by exocytosis

  
• MITOCHONDRIA STRUCTURE

  • double membrane with intermembrane space
  • inner membrane folded to form Crista
  • matrix inside the inner membrane with enzymes

  
• MITOCHONDRIA FUNCTION

  • site of aerobic respiration to produce ATP
  • cristae provide larger surface area for oxidative phosphorylation

  
• CHLOROPLAST STRUCTURE

  • small, flat organelle in photosynthesising cells
  • double membrane
  • thylakoids are flat discs with pigment / chlorophyll in and enzymes
  • grana - stacked thylakoids
  • Lamellae are flattened membranes which connect grana to transport chemicals
  • stroma is the fluid with starch granules in

  
• CHLOROPLAST FUNCTION

  • site of photosynthesis
  • light dependent on thylakoids and lamellae
  • light independent in stroma which contains enzymes for it
  • grana absorb light efficiently

  
• CELL WALL STRUCTURE

  • plants and algae - cellulose
  • fungi - chitin
  • bacteria - peptidoglycan, murein, glycoprotein

  
• CELL WALL FUNCTION

  • keeps shape of cell and prevents change of shape
  • supports and strengthens
  • osmosis - cell wall mechanically strong enough to resist hydrostatic pressure
  • permeable to water molecules

  
• VACUOLE STRUCTURE

  • permanent in plant cells
  • membrane sac, larger than vesicles
  • fluid filled - tonoplast
  • contains cell sap - weak solution of salts and sugars

  
• VACUOLE FUNCTION

  • maintains pressure inside cell
  • keeps cell rigid
  • stops plant wilting
  • isolation of unwanted chemicals
  • water in - hydrostatic pressure outwards, vacuole becomes turgid

  
• SPECIALISATION: the way cells adapt for their specific function to make function efficient
• HOW DOES SPECIALISATION HAPPEN?

  every cell has every gene to be able to become any cell, but only some genes are switched on / expressed and the rest are switched off
• EXAMPLES OF CELL SPECIALISATION

  • muscles cells —> lots of mitochondria, release ATP - help contraction
  • sperm cells —> lots of mitochondria and tail - to help them swim to egg
  • white blood cells —> lots of lysosomes - phagocytosis and digestion

  
• CELL ORGANISATION

  CELLS: the smallest unit that can live on its own and that makes up all living organisms and the tissues of the body.

  
• CELL ORGANISATION

  TISSUES: epithelial tissue lines surfaces of organs and have a protective and secretory function, xylem tissue transports water and mineral ions and has mechanical support.

  
• CELL ORGANISATION

  ORGANS: combination of tissues,

  • stomach has muscle to churn, epithelium to protect and secrete, connective tissue to hold tissues together
  • leaves have palisade mesophyll for photosynthesis, spongy mesophyll for gas diffusion, upper epidermis to protect and let light through, lower epidermis for protection and allow diffusion, xylem for transport of water and minerals and phloem for organic food

  
• CELL ORGANISATION

  ORGAN SYSTEM: organs work together as single unit

  • digestive system
  • respiratory system
  • circulatory system

  
• STRUCTURE OF PROKARYOTIC CELLS

  • less complex than eukaryotic
  • single celled organisms
  • smaller
  • no membrane bound organelles
  • more organelles
  • cell wall made of murein/ peptidoglycan
  • smaller ribosomes / 70s
  • DNA

  
• DNA IN PROKARYOTIC CELLS

  • free in cytoplasm
  • circular loop, coiled strand / not linear
  • plasmids are single loops which contain gene for antibiotic resistance

  
• ORGANELLES IN A PROKARYOTIC CELL

  NUCLEOID: not membrane bound region within bacteria, contains most bacterial DNA, some RNA and proteins, seen under TEM
• ORGANELLES IN A PROKARYOTIC CELL

  GENOPHORE: long, double strand of DNA, usually in a circle, most of genetic material, within nucleoid
• ORGANELLES IN A PROKARYOTIC CELL

  PLASMID: small, circular loops of DNA in cytoplasm, can be transferred between bacteria of same or different species