Eukaryotic cells and organelles

• cell surface membrane :

  • All cells are surrounded by a cell surface membrane which controls the exchange of materials between the internal cell environment and the external environment
  • The membrane is described as being ‘partially permeable’
  • The cell membrane is formed from a phospholipid bilayer of phospholipids spanning a diameter of around 10 nm

  
• Diagram of animal cell:

  contains:

  
• Plant cell diagram :

  contain=

  
• What do plant cells contain that animal cells don't ?

  1. cellulose cell wall
  2. plasmodesmata (channels for exchanging substances with adjacent cells)
  3. vacuole (compartment that contains cell sap)
  4. chloroplasts
  5. (you may see starch grains in plant cells but they are not organelles. Plants use starch grains to store excess sugars)
• algal and fungal cells:

  1. algal cells = a lot like plant cells - they have all the same organelles including a cell wall and chloroplasts
  2. Fungal cells = a lot like plant cells but have 2 key differences = their cell walls are made of chitin not cellulose and they don't have chloroplasts (don't photosynthesize)
• Eukaryotic cells =

  complex - including animal and plant cells and all cells in algae and fungi
• Nucleus :

  • large organelle surrounded by a double membrane (nuclear envelope) which has many pores
  • Nuclear pores are important channels for allowing mRNA and ribosomes to travel out of the nucleus, as well as allowing enzymes (eg. DNA polymerases) and signaling molecules to travel in
  • Controls the cells activities by controlling the transcription of DNA
  • The nucleus contains chromatin (the material from which chromosomes are made)
  • Chromosomes are made of sections of linear DNA tightly wound around proteins called histones
  • ‘nucleolus’ (plural: nucleoli) are the sites of ribosome production

  
• Mitochondria :

  • The site of aerobic respiration within eukaryotic cells, mitochondria are just visible with a light microscope
  • Surrounded by double-membrane with the inner membrane folded to form cristae
  • The matrix formed by the cristae contains enzymes needed for aerobic respiration, where ATP is produced
  • Small circular pieces of DNA (mitochondrial DNA) and ribosomes are also found in the matrix (needed for replication)
  • Found in large numbers in cells that ae very active and require a lot of energy

  
• Chloroplast:

  • Small, flattened structure found in plant and algal cells
  • surrounded by a double membrane and also has membranes inside called thylakoid membranes.
  • these membranes are stacked up in some parts of the chloroplast to form grana
  • Grana are linked together by lamellae - thin, flat pieces of thylakoid membrane
  • the site where photosynthesis takes place - some parts of photosynthesis happen in the grana and other parts happen in the stroma ( a thick fluid found in chloroplasts)

  
• Golgi Apparatus:

  • a group of fluid-filled membrane- bound flattened sacs
  • Vesicles are often seen at the edges of the sacs
  • It processes and packages new lipids and proteins
  • it also makes lysosomes

  
• Golgi Vesicles :

  • a small fluid-filled sac in the cytoplasm, surrounded by a membrane and produced by the Golgi apparatus
  • stores lipids and proteins made by the Golgi apparatus and transports them out of the cell (via the cell-surface membrane)

  
• Lysosome:

  • specialist forms of vesicles , a round organelle surrounded by a membrane - no clear internal structure
  • Contains hydrolytic enzymes. These are kept separate from the cytoplasm by the surrounding membrane, and can be used to digest invading cells or to break down worn out components of the cell/ organelles.

  
• Ribosomes:

  • a very small organelle that is found freely in the cytoplasm of all cells or is attached to the rough endoplasmic reticulum in eukaryotic cells
  • Each ribosome is made of ribosomal RNA (rRNA) and proteins
  • Its not surrounded by a membrane
  • 80S ribosomes are found in eukaryotic cells
  • 70S ribosomes are found in prokaryotes, mitochondria and chloroplasts
  • Site of translation (protein synthesis)

  
• Rough Endoplasmic Reticulum (RER)

  • a system of membranes enclosing a fluid-filled space called cisternae
  • the surface is covered with ribosomes
  • folds and processes proteins that have been made at the ribosomes

  
• Smooth Endoplasmic Reticulum (SER):

  • similar to rough endoplasmic reticulum (formed from a network of flattened membrane bound sacs called cisternae), but with no ribosomes
  • synthesizes and processes lipids & steroids
  • most cells contain less smooth ER compared to rough ER

  
• Cell wall:

  • Cell walls are formed outside of the cell membrane is a rigid structure offering structural support to cell in plants, algae and fungi
  • The cell wall is freely permeable to most substances (unlike the plasma membrane
  • Structural support is provided by the polysaccharide cellulose in plants and algae.
  • In fungi its made of chitin
  • Narrow threads of cytoplasm (surrounded by a cell membrane) called plasmodesmata connect the cytoplasm of neighboring plant cells

  
• Cell Vacuole:

  • a membrane-bound organelle found in the cytoplasm of plant cells
  • It contains cell sap - a weak solution of sugar and salts
  • The surrounding membrane is called the tonoplast
  • Helps to maintain pressure inside the cell and keep the cell rigid
  • This stops plants wilting
  • Also involved in the isolation of unwanted chemicals inside the cell