Eukaryotic cells

• Structure of the nucleus:

  - Nuclear envelope (double membrane)

  - Nuclear pores~ regulate exit and entry of materials

  - Nucleoplasm

  -Chromosomes~ protein-bound, linear DNA

  - Nucleolus~ smaller sphere inside which is the site of ribosomal RNA production and making ribosomes
• What are the functions of the nucleus?


  Site of DNA replication and transcription (making mRNA), contains the genetic code for each cell (houses chromosomes).
• What is the structure of the cell membrane?

  - It is a thin and flexible barrier

  - Phospholipids form the basic structure, with proteins embedded within it.

  - It is partially-permeable

  - The cell membrane also contains molecules/ receptors/ antigens on the surface allowing cell recognition/ signalling.
• What is the function of the cell membrane?

  It surrounds and protects the interior of the cell and controls the exchange of materials.
• Structure of mitochondria:

  - Surrounded by two membranes (an outer and inner)

  - The matrix~ central fluid filled space that contains enzymes that catalyse reactions in some stages of respiration

  - The cristae~ intricate folds of the inner membrane that have a large internal surface area and holds the enzymes involved in the final stages of respiration.

  - Contains circular DNA and ribosomes
• What is the function of mitochondria?

  Site of aerobic respiration and produces the energy carrier molecule, ATP.
• What is the structure of a ribosome?

  - small granules found in all cells (not surrounded by a membrane) and occur in large numbers

  - occurs free in the cytoplasm or associated with RER

  - made up of two subunits (large and small)

  - two types: 80s~ found in eukaryotic cells and are 25 nm in diameter

  70s~ found in prokaryotic cells, mitochondria and chloroplasts
• Functions of ribosomes:

  Site of protein synthesis: they contain ribosomal RNA and proteins.
• Golgi apparatus

  
• What is the structure of the golgi apparatus?

  Folded membranes making cisternae (stacks of flattened membranous sacs) ~secretory vesicles pinch off from the cisternae.
• What are the functions of the golgi apparatus?

  - Adds carbohydrates to proteins to form glycoproteins

  - Processes and packages new lipids and proteins

  - Produces secretory enzymes

  - Secretes carbohydrates (eg: cellulose in plants for making cell wall)

  - Makes lysosomes
• What are lysosomes?

  Vesicles produced by the Golgi apparatus containing lysozymes.
• What is the function of lysosomes?

  They contain hydrolytic enzymes used to destroy surplus organelles or body cells and tissues if released. They can release these enzymes to:

  . Breakdown material/ pathogens ingested by phagocytes

  . Destroy material outside the cell

  . Digest worn out organelles

  . Breakdown cells when they have died
• Rough ER

  
• What is the structure and function of the rough ER?

  - Extensive network of membrane-bound tubules and sacs

  - Continuous with the nuclear envelope

  - Ribosomes on the surface of the lipid membrane

  - Large SA for protein synthesis

  - Pathway to transport proteins through the cell
• What is the structure and function of the smooth ER?

  - No ribosomes, just an extension of the nuclear membrane (more tubular in appearance)

  - Synthesises, stores and transports lipids and carbohydrates

  
• What is the purpose of the vacuole?

  - The vacuole is filled with fluid and is surrounded by a single membrane called a tonoplast

  - It makes the cell turgid so provides support

  - Temporary store of sugar and amino acids

  - The pigments are responsible for coloured petals

  - Stops the plant wilting and is involved in the isolation of unwanted chemicals.
• What is the structure of the cell wall?

  - A rigid structure that surrounds cells in plants, algae and fungi.

  - There is a thin layer called the middle lamella which cements adjacent cells together.

  - Plants and algae~ made of microfibrils of cellulose polymer

  - Fungi~ made of chitin
• What is the cell wall's function?

  Provides mechanical strength to the cell and prevents the cell from bursting by pressure from osmosis.
• What is the structure of the chloroplast?

  - Present in plant and algal cells

  - Surrounded by two membranes, forming an envelope

  - The stroma~ contains water, enzymes and other substances

  - Thylakoids~ intricate series of membranes that form interconnecting enclosed spaces, contains the chlorophyll

  - Grana~ stacks of thylakoids

  - Lamellae~ adjacent grana are connected by the lamella
• What is the function of the chloroplast?

  The site of photosynthesis~ some parts happen in the grana and others in the stroma
• What is chromatin?

  Loosely packed DNA spread throughout the nucleoplasm.
• What are chromosomes?

  DNA condensed into thread like structures during cell division.
• Nucleus

  
• Mitochondria

  
• Chloroplast

  
• What are centrioles?

  Paired, barrel-shaped organelles located in the cytoplasm of animal cells near the nuclear envelope. They are made of microtubules and help chromosomes separate during cell division.