cell structure

• structure of nucleus

  1. Nuclear envelope: double membrane surrounding nucleus, outer membrane continuous with the (R)ER of the cell.

  
  

  2. Nuclear pores: allow the passage of larger molecules, such as mRNA, out of the nucleus.

  
  

  3. Nucleoplasm: granular, jelly-like material making up the bulk of the nucleus.

  
  

  4. Chromosomes: protein-bound, linear DNA.

  
  

  5. Nucleolus: small spherical region(s) in nucleoplasm. Manufactures ribosomal RNA and assembles ribosomes.

  
• Funtion of nucleus

  1. site of DNA replication and transcription

  2. contains genetic code for each cell
• structure of smooth endoplasmic reticulum

  -enclosed flattened sacs with nuclear membrane

  -Has no ribosomes on its surface.

  
• function of smooth endoplasmic reticulum

  Synthesises, stores and transports lipids, carbohydrates and steroid hormones
• Structure of rough endoplasmic reticulum

  -enclosed flattened sacs with nuclear membrane.

  -Is coated with Ribosomes.

  
• function of rough endoplasmic reticulum

  • large SA for protein synthesis
  • pathway for transport of materials
• Structure of Golgi Apparatus

  1. Compact system of flattened sacs and stacked membranes (cisternae).

  
  

  2. Vesicles - modified proteins and lipids transported to cell membrane where they fuse with it, and then egest contents to the outside.

  
• function of golgi apparatus


  - Modify, sorts and packages proteins and other materials from the ER for storage in the cell or secretion outside the cell

  - forms glycoproteins

  -produce secretory enzymes

  -forms lysomes
• Structure of Lysosomes

  Membrane sac of digestive enzymes

  contain lysozymes

  
• function of lysosomes

  - digest/break down food, waste, and broken parts

  - hydrolyse phagocytic cells

  - exocytosis - release enzymes to outside of cell to destroy material
• structure of mitochondria

  1. Double membrane surrounding organelle - controls entry and exit of material.

  
  

  2. Cristae - extensions of the inner membrane, providing a large surface area for the attachment of enzymes and other proteins during respiration.

  
  

  3. Matrix - makes up the remainder - contains proteins, lipids, ribosomes and DNA (allows mitochondria to produce own proteins) and some respiratory enzymes.

  
• function of mitochondria

  - Site of aerobic respiration

  - ATP production

  - DNA to code for enzymes needed in respiration
• structure of ribosomes

  1. Small cytoplasmic granules found in all cells, free-floating or associated with RER.

  
  

  2. 80S - found in eukaryotic cells, slightly larger.

  
  

  3. 70S - in prokaryotic cells, slightly smaller.

  
  

  4. 2 Subunits - large and small - contain ribosomal RNA and proteins.

  
• function of ribosomes

  site of protein synthesis
• Structure of vacuole

  -A fluid filled sac surrounded by a tonoplast membrane.

  
• function of vacuole

  - Filled with cell sap which helps keep the cell turgid

  - temporary store of sugars and amino acid
• structure of chloroplasts

  1. Chloroplast envelope - double plasma membrane, highly selective, surrounds the organelle.

  
  

  2. Grana - stacks of disc-shaped thylakoid membrane.

  
  

  3. Thylakoids - contain chlorophyll used in photosynthesis, can be linked by lamellae to other grana.

  
  

  4. Stroma - fluid-filled matrix where Calvin Cycle takes place. Also contains starch grains.

  
• function of chloroplast

  Site of photosynthesis
• structure of cell wall in plants

  made from microfribrilis which is made from cellulose

  
• structure of cell wall in fungi

  made from chitin
• Function of cell wall


  Protects and supports the cell
• structure of plasma membrane

  phospholipid bilayer

  
• function of plasma membrane

  controls entrance and exit of molecules
• what features of plant cells are NOT in animal cells?

  cell wall, vacuole, chloroplast
• name 3 key differences between prokaryotic and eukaryotic cells

  - cells are much smaller (P)

  - no membrane bound organelles (P)

  - no nucleus ( P)

  - cell wall made of murein (P)
• What is the size of ribosomes in prokaryotes?

  70s
• what is the size of ribosomes in eukaryotic cells

  80s
• what do prokaryotic cells have, instead of a nucleus


  a single, circular DNA molecule free in the cytoplasm
• what do prokaryotic cell walls contain

  murein (glycoprotein)
• what is a plasmid?


  small circular piece of DNA (prokaryotic)
• what is the capsule?

  slimy layer made of protein

  prevents the bacteria from drying out and protects it from the host immune system
• what is the function of flagella

  - rotate at the base to propel the bacteria for movement
• What is cell fractionation used for?

  Separating individual organelles from the cell in order to study
• what 3 things does the solution need to be in cell fractionation?

  cold, isotonic and buffered
• why does the solution need to be cold in cell fractionation?

  - to reduce enzyme activity

  - when the cell is broken open, enzymes are released which could damage organelles
• why does the solution need to be isotonic in cell fractionation?

  - organelles need to be the same water potential as the solution to prevent osmosis

  - stops organelles from shrivelling or bursting
• why does the solution need to be buffered in cell fractionation?

  - solution has a pH buffer to prevent damage to organelles
• name the two steps of cell fractionation

  1. homogenisation

  2. ultracentrifugation
• what occurs in homogenisation

  - cells are broken open using a blender

  - whilst in cold, isotonic, buffered solution
• What occurs in ultracentrifugation?

  - filtered solution spun in a centrifuge, with increasing speeds each time

  - separates organelles according to density