Chapter 3- Cell Structure Flashcards
Magnification =
Size of image / size of real object
What is resolution?
Minimum distance apart that two objects can be in order for them to appear as separate items
What is cell fractionation?
Process where cells are broken up + organelles are separated out
What are the 3 steps of cell fractionation?
- Tissue is placed in a cold, buffered, same water potential solution
- Homogenation
- Ultracentrifugation
Describe homogenation
-Cells broken up by homogeniser
-Releases organelles from cells
-Resultant fluid = homogenate -> filtered
Describe ultracentrifugation
Ultracentrifugation = fragments in homogenate are separated in centrifuge
1. Filtrate placed in centrifuge + spun (slow speed)
2. Heaviest organelles (nuclei) spun to bottom of tube
3. Fluid at top (supernatant) removed (leaves nuclei sediment)
4. Supernatant -> other tube + spun at faster speed
5. Next heaviest organelles (mitochondria) forced to bottom
6. Process repeated at faster speed each time so each organelles is sedimented + separated
What is a transmission electron microscope (TEM)?
-Parts of specimen absorb electrons + appear dark -Produces image on screen + photographed -> photomicrograph
-Resolving power = 0.1nm (limited by specimen preparation + electron beam damaged specimen)
What are the limitations of the TEM?
-Must be in a vacuum - X observe living specimens
-Specimen needs complex staining process but image X in colour
-Specimen = extremely thin
-Produces a flat 2D image
-Image may have artefacts
How does a scanning electron microscope (SEM) work?
-Specimens X need to be extremely thin - electrons don’t penetrate
-Directs electron beam onto specimen depending on contours of specimen
-Resolving power = 20nm
What is an eyepiece graticule?
Placed in eyepiece of microscope + scale is etched onto it + then its calibrated for each objective lens then it can remain in place
Structure + function of nucleus
-Nuclear envelope = double membrane, controlling entry/exit + contains everything
-Nucleolus = small spherical, assembles ribosomes
-Chromosomes = protein-bound, linear DNA
-Nucleoplasm = majority of nucleus, jelly-like
-Nuclear pores = allow passage of large molecules e.g. mRNA
-Function = Contains genetic info, control centre
Structure + function of mitochondria
-Cristae = part of inner membrane, large SA (protein + enzyme attachement)
-Double membrane = controls entry/exit
-Matrix = contains proteins, lipids, ribosomes + DNA -> mitochondria can control protein production
-Function = aerobic respiration, ATP production
Structure + function of chloroplasts
-Chloroplast envelope = double membrane, selective entry/exit
-Stroma = where 2nd photosynthesis stage happens
-Grana = stack of disc-like structures called thylakoids containing chlorophyll, where light absorption happens
-Granal membrane = large SA, chemical can attached for 1st photosynthesis stage
-Manufactures proteins for photosynthesis -> ribosomes + DNA
Structure + function of ribosomes
-Two types -> 80S (eukaryotic) + 70S (prokaryotic cells, mitochondria, chloroplasts + are smaller)
-Function = site of protein synthesis
Structure + function of endoplasmic reticulum
Rough (RER):
-Ribosomes present
-Functions: large SA -> protein synthesis, pathway for material transport through cell
Smooth (SER):
-No ribosomes
-Functions: synthesis/store/transport lipids + carbohydrates
Structure + function of Golgi apparatus
-Cisternae = stack of membranes
Functions:
-Add carbohydrates to proteins -> glycoproteins
-Produce secretory enzymes
-Secrete carbohydrates
-Transport lipids
-Form lysosomes
Structure + function of lysosomes
-Lysozymes -> hydrolyse cell wall of bacteria
Functions:
-hydrolyse material ingested by phagocytes
-release enzymes out of cell to destroy materials
-digest old organelles to reuse chemicals
-break down dead cells
Structure + function of cell wall
-Middle lamella = boundary between adjacent cell walls
-Made of polysaccharides
Functions:
-Mechanical strength
Cell walls of fungi made of chitin
Structure + function of vacuoles
-Single membrane around = tonoplast
Functions:
-supports plants = makes cells turgid
-sugars + amino acids = temporary food store
-pigments -> colour petals -> attract insects
How do cells become specialised?
Only having some genes expressed at one time -> different genes switched on in different specialised cells -> makes it adapted to a particular function which it performs effectively to make an organism efficient
What are tissues?
Collection of similar cells performing a similar function e.g. epithelial tissues -> often line organ surfaces as protection/to secrete
What are organs?
Combination of tissues performing variety of functions, often having one predominant function e.g. animals = stomach, plants = leaf
What is an organ system?
Organs working together to perform particular functions e.g. digestive = digest + process food
Function of a cell wall in prokaryotes
Made of murein
Physical barrier to protect from substances + mechanical damage
