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Flashcards in 5 - Cells Deck (34):

Structure of cell membrane?

Made of phospholipid bilayer
Intrinsic and extrinsic proteins
Controls the entry and exit of materials
Non-polar molecules can diffuse through
Polar molecules move through using channel or carrier proteins


Structure of nucleus?

Surrounded by nuclear envelope
Nuclear pores - gaps in the nucleus
Chromatin inside - where the DNA is kept
Nucleolus - Dark parts of chromatin - makes ribosomes


Structure of mitochondrion?

Site of aerobic respiration
Double membrane
Inner membrane folded into Cristae
The space inside the mitochondria is called the Matrix


Structure of Chloroplast?

Site of photosynthesis
Third membrane called thylakoid
Space inside chloroplast is called stroma
contains Circular Granum and Starch Grains


Use of Golgi Apparatus?

Transport proteins from the RER and SER to the cell membrane
Modification and packaging of proteins takes place
Made of flattened sacs filled with fluid


Use of lysosomes?

Contain digestive enzymes to break down unwanted chemicals, cells, toxins, etc.


Use of Ribosomes?

Protein synthesis


Use of RER and SER

RER - Protein synthesis on ribosomes
SER - Lipid synthesis


Structure of cell wall?

Made of strong cellulose fibres
Outside of cell wall called middle-lamella
Gaps between cell walls called plasmodesmata


Structure of vacuole?

Have a central vacuole
Contain cell sap
Membrane called tonoplast


Structure of prokaryotic cells?

No nucleus - DNA present in nucleus
Most are unicellular (single cell)
Have ribosomes - similarity to Eukaryotic cells
Circular cells called plasmids that contain more genetic information
Cell wall not made of cellulose or chitin but from murein
Extra layer outside of cell wall called capsule


Virus structure

Surrounded by protein coat called capsid
Said to be acellular - not made of cells
According to cell theory they are not living
Contain genetic material inside that floats
Have attached proteins on the outside
Viruses are extremely small


Virus replication

Invade cell
protein molecules on capsid attach to membranes
Genetic material hijaks the machinery of cell
Cell copies viruses DNA
Creates new viruses
Virsuses burst out of cell, destroying it


Magnification formula?

M = Image/ Actual


Optical microscope?

Objective lens at bottom
Eyepiece lens at top
Condenser lens underneath
Limited resolving power due to the wavelength of light (resolving power limited to half the wavelength of light, most powerful at 0.2um)
Magnification x1500


What is resolving power?

The ability to distinguish between two objects


What is magnification?

The number of times bigger an image is than the actual object


Electron microscope?

Specimens stained with heavy metals
Does not let electrons through
In vacuum (electrons can only pass through air for a little distance)
Electron gun at top
electromagnet lens focuses electrons onto specimen
objective lens underneath specimen, goes to projector lens
Goes to fluorescent screen
Image black and white
Resolving power: 0.0002um due to electron wavelength being very small
Magnification: x1,500,000
Specimens are dead (in vacuum) however and are cut thin


Differences between TEMs and SEMs?

- High resolution images
- Shows internal parts of organelles
- Only used on thin specimens
- Show the surface and can be 3D
- Lower resolution images
- Can be used on thick specimens


What can occur in the preparation of any electron microscopy?

Artefacts, images that are not there in real life


Cell fractionation and centrifugation?

Separating the parts and organelles in a cell so that they can be studied closely


Process of differential centrifugation?

1. Use homogeniser to break open cell membrane/wall
2. Buffer solution to keep pH the same and prevent enzyme or protein denaturing
3. Add isotonic solution (same water potential as cell) to keep the osmotic movement the same so cells do not burst or shrink
4. Filter to remove debris such as the broken cell wall
5. Centrifugation: homogenate is centrifuged at different speeds to operate organelles based on their size/density, largest first.
Pellet of organelle will remain at bottom whilst supernatant will be at top after spinning


Examples of density of organelles?

Very dense Nucleus
Golgi, lysosomes, RER
Lease dense Ribosomes


Cell cycle?

Interphase (G1, S, G2)
Mitosis (Prophase, Metaphase, Anaphase, Telophase)


What happens in interphase?

G1 - Cell increases in size and mass, organelle and protein synthesis
S - DNA replication, Increased respiration
G2 - Protein synthsesis


Process of mitosis?

Prophase: Chromosomes condense and become visible, chromatids held by centromere and nuclear membrane breaks down
Metaphase: Chromosomes line up at centre of cell, spindle fibres attach at the centromeres
Anaphase: Chromatids separated to opposite poles of cell, Spindle fibres contracts
Telophase: Chromosomes uncoil, new nuclear membrane forms around the chromosomes
Cytokinesis: Cellular division and two genetically identical daughter cells are produced with full set of chromosomes


Importance of mitosis?

Replace and repair cells
Forms genetically identical cells
Asexual reproduction


Cancer due to cell cycle

Mutations in DNA can occur through additions, deletions or subsititutions
Uncontrolled cell division leads to growth of tumour


Cell division in prokaryotes?

Do not have chromosomes so divide by binary fission
Circular DNA and any plasmids replicate and move to opposite poles of the cell
Main DNA loop is only replicated once
The cell splits and forms two daughter cells with identical genetic information
Plasmids may not divide equally however


Calculating time taken for each stage for mitosis

Proportion of cells in that phase x how long the cell cycle lasts in minutes


Root tip observation of cells experiment

Cut 1cm from the tip of a growing root (tip where mitosis occurs)
Prepare a boiling tube containing 1 M hydrochloric acid and put it in a water bath at 60 C
Transfer the root tip in to a boiling tube and leave for 5 mins
Use a pippete to rinse the root tip with cold water and dry on paper towel
Cut 2mm of the very tip and place on microscope slide
Use a mounted needle to break the tip open and spread the cells out thinly
Add a few drops of stain (toluidine blue O)
Place a cover slip over, push down firmly, don't smear
Can view through optical microscope


Mitotic Index

Number of cells with visible chromosomes / total number of cells observed


Calculating size of cells

Line up eyepiece graticule and the stage micrometer
Each division on the stage micrometer is 0.1mm long
At this magnification, 1 division on the stage micrometer is the same as 4.5 divisions on the eyepiece graticule
Therefor 1 division on the eyepiece graticule is 0.22 mm
Find how many eyepiece divisions and use this number


How to prepare slides?

Pipette small drop of water onto slide
Tweezers to place small thin specimen on top of water
Add a stain
Add cover slip