cell structure

• Define a eukaryotic cell

  DNA is contained in a nucleus, contains membrane-bound specialised organelles.
• Define a Prokaryotic cell

  DNA is 'free' in cytoplasm, no organelles e.g. bacteria & archaea.
• State the relationship between a system and specialised cells.

  Specialised cells → tissues that perform specific function → organs made of several tissue types → organ systems
• Describe the structure of the cell-surface membrane.

  Fluid mosaic' phospholipid bilayer with extrinsic & intrinsic proteins embedded

  
• Describe the function of the cell-surface membrane

  ● Isolates cytoplasm from extracellular environment.

  ● Selectively permeable to regulate transport of

  substances

  
• Explain the role of cholesterol

  steroid molecule connects phospholipids & reduces fluidity
• Explain the role of glycoproteins

  cell signalling, cell recognition (antigens) & binding cells together

  
• Explain the role of glycolipids

  cell signalling & cell recognition

  
• Describe the structure of the nucleus


  ● Surrounded by nuclear envelope, a semi-permeable double membrane.

  ● Nuclear pores allow substances to enter/exit.

  ● Dense nucleolus made of RNA & proteins assembles ribosomes.

  
• Describe the function of the nucleus

  ● Contains DNA coiled around chromatin into chromosomes.

  
  

  ● Controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis, semiconservative replication
• Describe the structure of a mitochondrion


  ● Surrounded by double membrane folded inner membrane forms cristae: site of electron transport chain

  ● Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins.

  
• Describe the structure of a chloroplast

  ● Vesicular plastid with double membrane.

  
  

  ● Thylakoids: flattened discs stack to form

  grana; contain photosystems with chlorophyll.

  
  

  ● Intergranal lamellae: tubes attach thylakoids

  in adjacent grana.

  
  

  ● Stroma: fluid-filled matrix

  
• State the function of mitochondria

  site of aerobic respiration to produce ATP

  
• State the function of chloroplasts

  site of photosynthesis to convert solar energy to chemical energy
• Describe the structure and function of the Golgi apparatus.


  Planar stack of membrane-bound, flattened sacs cis face aligns with rER.

  
  

  Molecules are processed in cisternaevesicles bud off trans face via exocytosis:

  ● modifies & packages proteins for export

  ● synthesises glycoproteins

  
• Describe the structure of a lysosome

  - Sac surrounded by single membrane

  - embedded H+ pump maintains acidic conditions

  - contains digestive hydrolase enzymes

  - glycoprotein coat protects cell interior

  
• Describe the function of a lysosome

  ● digests contents of phagosome

  ● exocytosis of digestive enzymes
• Describe the structure of a ribosome

  Formed of protein & rRNAfree in cytoplasm or attached to ER

  
• Describe the function of a ribosome

  ● Site of protein synthesis via translation:

  large subunit: joins amino acids

  small subunit: contains mRNA binding site
• Describe the structure of the endoplasmic reticulum (ER).


  Cisternae: network of tubules & flattened sacs extends from cell membrane through cytoplasm & connects to nuclear envelope

  
• Describe the function of a rough endoplasmic reticulum (ER)

  many ribosomes attached for protein synthesis & transport.

  
• Describe the function of a smooth endoplasmic reticulum (ER)


  lipid synthesis

  
• Describe the structure of the cell wall in bacteria

  Made of the polysaccharide murein.

  
• Describe the structure of the cell wall in plants

  - Made of cellulose microfibrils

  - plasmodesmata allow molecules to pass between cells

  - middle lamella acts as boundary between adjacent cell walls.
• State the functions of the cell wall

  ● Mechanical strength and support.

  ● Physical barrier against pathogens.

  ● Part of apoplast pathway (plants) to enable easy diffusion of water
• Describe the structure of the cell vacuole in plants.

  Surrounded by single membrane: tonoplastcontains cell sap: mineral ions, water, enzymes, soluble pigments.

  
• Describe the function of the cell vacuole in plants

  ● Controls turgor pressure.

  ● Absorbs and hydrolyses potentially harmful

  substances to detoxify cytoplasm
• Explain some common cell adaptations

  ● Folded membrane or microvilli increase surface area e.g. for diffusion.

  ● Many mitochondria = large amounts of ATP for active transport.

  ● Walls one cell thick to reduce distance of diffusion pathway
• State the role of plasmids in prokaryotes

  ● Small ring of DNA that carries non-essential genes.

  ● Can be exchanged between bacterial cells via conjugation.

  
• State the role of flagella in prokaryotes

  Rotating tail propels (usually unicellular) organism
• State the role of the capsule in prokaryotes.

  polysaccharide layer:

  
  

  ● Prevents desiccation.

  ● Acts as food reserve.

  ● Provides mechanical protection against

  phagocytosis & external chemicals.

  ● Sticks cells together.

  
• what do both eukaryotic and eukaryotic cells have ?

  ● Cell membrane.

  ● Cytoplasm.

  ● Ribosomes (don't count as an organelle since not membrane-bound).
• Why are viruses referred to as 'particles' instead of cells?

  Acellular & non-living: no cytoplasm, cannot self-reproduce, no metabolism.
• Describe the structure of a viral particle

  ● Linear genetic material (DNA or RNA) & viral enzymes e.g. reverse transcriptase.

  ● Surrounded by capsid (protein coat made of capsomeres).

  ● No cytoplasm

  
• Describe the structure of an enveloped virus

  ● Simple virus surrounded by matrix protein.

  ● Matrix protein surrounded by envelope derived from cell membrane of host cell.

  ● Attachment proteins on surface

  
• State the role of the capsid on viral particles

  ● Protect nucleic acid from degradation by restriction endonucleases.

  
  

  ● Surface sites enable viral particle to bind to & enter host cells or inject their genetic material

  
• State the role of attachment proteins on viral particles

  Enable viral particle to bind to complementary sites on host cell : entry via endosymbiosis

  
• Describe how optical microscopes work

  1)Lenses focus rays of light and magnify the view of a thin slice of specimen.

  
  

  2) Different structures absorb different amounts and wavelengths of light.

  
  

  3) Reflected light is transmitted to the observer via the objective lens and eyepiece
• Outline how a student could prepare a temporary mount of tissue for an optical microscope

  1) Obtain thin section of tissue e.g. using ultratome or by maceration.

  
  

  2) Place plant tissue in a drop of water.

  
  

  3) Stain tissue on a slide to make structures visible.

  
  

  4) Add coverslip using mounted needle at 45° to

  avoid trapping air bubbles
• give advantages of using an optical microscope

  + colour image

  + can show living structures

  + affordable apparatus