3+4 Cell structure + Transport across membranes

• In eukaryotic cells, the cytoplasm contains membrane-bound organelles so DNA is enclosed in a nucleus
• Organelle = sub-cellular structure with a specific function
• Membrane-bound = surrounded by a membrane (phospholipid bilayer)
• Examples of eukaryotic organisms: animals, plants, algae and fungi
• General animal cell organelles:

  • Mitochondria
  • Nucleus and nucleolus
  • Rough and Smooth endoplasmic reticulum
  • Golgi apparatus and golgi vesicle
  • Cytoplasm
  • Ribosomes
  • Lysosomes
  • Cell-surface membrane
• Cell wall can be found in plants, algae and fungi
• chloroplasts can be found in plants and algae
• large, permanent cell vacuole can only be found in plants
• The cell surface membrane is a selectively permeable barrier between the cell and its environment so it enables the control of the passage of substances in and out of the cell.
• The cell-surface membrane contains molecules/receptors/antigens on the surface allowing cell recognition/signalling
• The nucleus is made up of a nuclear envelope, the nucleolus, the nucleoplasm and protein-bound, linear DNA
• The nucleus contains DNA which contains genes which code for protein so it controls cell activities
• The nucleolus makes ribosomes
• Nuclear pores allow substances e.g. mRNA to move between the nucleus and the cytoplasm
• The nuclear envelope has a double membrane and nuclear pores
• The nucleolus is the dense region within the nucleus
• Ribosomes are the site of protein synthesis - translation
• Ribosomes are not surrounded by a membrane but can be attached to the rough endoplasmic reticulum
• Ribosomes are made of ribosomal RNA and a protein
• Rough endoplasmic reticulum roles:

  1. Ribosomes on the surface of the rough endoplasmic reticulum synthesise proteins
  2. Proteins are processed/folded/transported inside the rough endoplasmic reticulum
  3. Proteins are packaged into vesicles for transport e.g. to Golgi apparatus
• The smooth endoplasmic reticulum synthesises and processes lipids e.g. cholesterol
• The smooth endoplasmic reticulum has NO ribosomes attached to it
• Golgi apparatus role:

  1. Modifies/Processes protein from the rough endoplasmic reticulum e.g. protein + carbohydrate -> glycoproteins
  2. Packages them into Golgi vesicles
  3. Produces lysosomes (a type of Golgi vesicle)
• Golgi vesicles transport proteins or lipids to their required destination e.g. to the cell-surface membrane
• Lysosomes have a membrane and contain lysozymes (hydrolytic enzymes)
• Lysosomes role:

  1. Contains/releases lysozymes
  2. To break down/hydrolyse pathogens or worn-out cell components
• The mitochondria consists of an outer membrane, cristae (inner membrane fold) and the matrix (which contains small 70S ribosomes and circular DNA)
• The mitochondria is the site of aerobic respiration to produce ATP for energy release
• Chloroplasts consist of:

  • A double membrane
  • Stroma, which contains thylakoid membrane, small 70S ribosomes, circular DNA and starch granules or lipid droplets
  • Lamella, which is the thylakoid linking grana
  • Grana, which are stacks of thylakoid
• Chloroplasts absorb light energy for photosynthesis to produce organic substances
• The cell wall in plants and algae is composed mainly of cellulose (a polysaccharide)
• The cell wall in fungi is composed of chitin (a nitrogen-containing polysaccharide)
• The cell wall provides mechanical strength to the cell so prevents cell changing shape or bursting under pressure due to osmosis. It is permeable to most substances unlike the cell-surface membrane
• The cell vacuole maintains turgor pressure in the cell, supporting the plants. It also contains cell sap - a store of sugars, amino acids, pigments and any waste chemicals
• A tissue is a group of specialised cells with a similar structure working together to perform a specific function, often with the same origin
• An organ is a group of tissues performing specific functions
• An organ system is a group of organs working together to perform specific functions
• Antibodies, enzymes and hormones need a high rate of protein production so they have many ribosomes and rough endoplasmic reticulum for a high rate of protein synthesis
• Many cells need a high rate of ATP production - e.g. for active transport or muscle contraction so they have many mitochondria for a high rate of aerobic respiration/ATP production
• Bacteria and archaea (always unicellular) are prokaryotic organisms