Unit 2- Cell Structure Flashcards
What does cell theory state? 3
- all organisms are composed of 1 or more cells, all the processes of life take place within these cells
- Cells are the smallest units that can be alive
- New cells are always formed by division of old cells
How do unicellular and multicellular organisms differ, in terms of cells
- unicellular, the cell carries out all the processes of life
- multicellular, the cells are differentiated to carry out different tasks
Difference between prokaryotic and eukaryotic cells?
Prokaryotic cells have no nucleus or interior compartments
Eukaryotic cells have a nucleus and various interior compartments
Cell membrane:
- thin flexible layer made of phospholipids and proteins
- controls entry and exit of materials
- separates the contents of the cell from the outside
Nucleus:
- surrounded by a nuclear envelope, a double membrane with nuclear pores
- interior nucleoplasm, full of chromatin
- in cell division chromatin condenses becoming visible chromosomes
- nucleolus, used in making ribosomes
Mitochondria:
- where aerobic respiration occurs, and ATP is synthesised
- double membrane, outer is simple and very permeable while inner is highly folded to give cristae
- cristae, provide large surface area
- mitochondrial matrix, containing small circular strands of DNA
- stalked particles (ATP synthase) on cristae
Chloroplasts:
- where photosynthesis takes place
- found in only photosynthetic organisms
- double membrane
- starch grain
- thylakoid membrane folded into disks
- stacks of thylakoid membranes are called grana
- space between membranes is called stroma
- thylakoid membrane contains chlorophyll and carotenoids
What is a plastid?
Organelles with a double membrane, which divide by fission
Ribosome:
- sites of protein synthesis
- smallest organelle
- found free in the cytoplasm or on RER
RER
- studded with ribosomes for protein synthesis
- proteins are processed in the RER, eg modified by adding a carb group)
- exported to the Golgi apparatus after modified
SER
- processes/modifies materials, mainly lipids
- modified compounds are sent to Golgi to be transported out the cell
Golgi Apparatus:
- series of flattened membranes
- purpose is to transport proteins for extra cellular use from the ER to the cell membrane
- parts of the RER fuse with the Golgi body to form cisternae, pushing a vesicle of proteins off from the cisternae
- vesicles release their contents out the cell by exocytosis
Vacuoles:
- Membrane bound sacs containing water or dilute solutions of salts and other solutes
- plant cell vacuoles are surrounded by a membrane called the tonoplast, filled with sap
- they keep cell rigidity and turgidity
Lysosomes:
- membrane bound vesicles containing digestive enzymes
- formed from RER
- used to break down toxic chemicals, organelles or cells, where the products are then recycled in the cell
- may fuse with phagosomes
Cytoskeleton:
- network of protein fibres throughout all eukaryotic cells
- add support, transport and motility
- attached to the cell membrane providing shape holding organelles in position
- responsible for cell movements such as division, cilia, flagella…
Centrioles:
- 2 centrioles found near the nucleus
- part of the cytoskeleton
- used in cell division to make up spindle fibres
- only in animal cells
Cilia purpose:
To move the cell or extra cellular fluid
Short and numerous
Flagella purpose:
- longer than the cell
- used for motility, eg sperm
Microvilli purpose:
- short extensions found in epithelial cells of small intestine and kidney
- increase the surface area for absorption
Cytoplasm:
- solution within cell membrane
- contains enzymes, sugars, salts, amino acids, nucleotides and all the resources needed for a cell to function
Cell wall:
- thick layer outside the cell membrane
- used to give strength and rigidity to cells
- resists osmotic lysis
Give examples of cell walls:
- plant- cellulose
- fungi- chitin
- bacteria- peptidoglycan
Plant cell walls composition:
- 3 layers:
1) outer layer is the middle lamella, thick layer of calcium pectate that glues cells together
2) middle layer is the primary cell wall, thin layer of cellulose microfibrils and is more flexible
3) the inner layer is the secondary cell wall, thick, network of of fibres like cellulose, hemicellulose and pectin
What makes up the primary cell wall?
Cellulose microfibrils
What makes up the outer layer of the cell wall?
- middle lamella
Made of calcium pectate (glue like substance)
What is special about xylem cells?
The secondary cell wall contains additional lignin for strength and water proofing, which later form woody tissue
What makes up the inner layer of the cell wall?
- secondary cell wall
- network of fibres including cellulose, hemicellulose and pectin
What is the plasmodesmata?
Channels between cytoplasm of adjacent cells forming a symplast, allowing solutes to diffuse freely between cells without crossing a membrane
What is the difference between prokaryotic and eukaryotic ribosomes?
Prokaryote have 70s ribosomes (made of 30s and a 50s subunit)
Eukaryotes have 80s ribosomes
Compare and contrast the eukaryotic and prokaryotic cells
- both have DNA as genetic material
- both have a membrane
- prokaryotes have 70s ribosomes and eukaryotes 80s ribosomes
- prokaryotes do not have membrane bound organelles
What are the 9 organelles found in all prokaryotes
- cell membrane
- cytoplasm
- cell wall
- capsule
- DNA
- plasmid
- nucleoid
- flagellum
- 70s ribosomes
Describe the capsule, and its function
- thick sticky layer of sugar (polysaccharides)
- used to stick cells together, for a food reserve, protection
What are plasmids?
Small circles of DNA, separate from main DNA in prokaryotes used to exchange DNA in bacteria
What is the nucleoid?
Region of cytoplasm where main DNA of prokaryote is
What is the flagellum?
A rigid helical shaped tail used for propulsion
What are the results of the gram stain test?
Gram positive bacteria stain purple
Gram negative bacteria stain red
Describe the structure of a gram positive cell wall
- capsule
- very thick peptidoglycan cell wall
- phospholipid bilayer
What is a positive and negative feature of gram positive bacteria
+ thick cell wall provides lots of strength against physical conditions
- most antibiotics act on wall formation so these are more vulnerable
Describe the structure of the gram negative cell wall
- lipopolysaccharide bilayer
- thin layer of peptidoglycan
- thin layer of cytoplasm (periplasm)
- phospholipid bilayer (cell membrane)
Give a positive and negative feature of gram negative bacteria
+ thin cell wall provides less strength so is more easily broken
- outer layer of lipopolysaccharides is resistant against most antibiotics, so these are harder to kill
Describe the gram stain test
- add crystal violet stain to slide, (binds to peptidoglycan turning ALL bacteria purple)
- iodine assists the binding process
- add ethanol (dissolves outer lipid layer of gram negative) this washes out purple stain from gram negative but not gram positive
- add safranin (red stain) which binds to remaining peptidoglycan of gram negative
