(3) Cell Structure Flashcards
Explain how to separate organelles in cell fractionation.
Before cell fractionation:
Tissue placed in cold, buffered isotonic solution.
Cold- Reduces enzyme activity that may break down organelles
Buffered- To maintain pH which could affect structure of organelles.
Isotonic- To prevent osmosis/organelles from bursting or shrinking.
Ultracentrifugation:
Tube of filtrate spun at high speed
Heaviest organelles move to the end creating a pellet and supernatant
Pellet removed and supernatant spun again at faster speed.
Largest- smallest:
Nucleus mitochondria lysosomes ribosomes
Electron Microscope advantages and disadvantages:
Electron beam very short wavelength hence resolve objects very well.
Electrons negatively charged beam can be focused using electromagnets.
TEM:
Electron beam penetrates specimen
Produces 2D images
Requiring thin specimen
Very high resolution
SEM:
Electron beam does not penetrate
Electrons are scattered off specimen and detected
Produces 3D image
Does not require specimen to be thinly sliced.
Lower resolution than TEM
Disadvantages for both:
Must be in a vacuum
Requires complex staining process
Which may lead to artefacts
Describe the structure and functions of the nucleus. (4marks)
Overall function:
Production of mRNA and DNA
Hence protein synthesis
Store of DNA and Chromosomes
Nuclear envelope- Double membrane surrounding the nucleus. Controls entry and exit of materials in and out of cell
Nuclear pores- Allows passage of large molecules eg. mRNA out of nucleus.
Nucleoplasm- granular, jelly like material makes up the bulk of the nucleus.
Chromatin- loose DNA found within nucleoplasm.
Nucleolus- Small spherical region within nucleoplasm. Manufactures ribosomal DNA: assembles the ribosomes.
Describe structure of Mitochondria.
Mitochondria:
Site of aerobic respiration
Production of ATP
Cristae: Provide large surface area for the attachment of enzymes and other proteins involved in respiration
Matrix:
Makes up remainder of mitochondria.
Contains: Proteins, lipids and DNA
So mitochondria can produce some of its own proteins.
Describe the structure and functions of the chloroplasts.
Chloroplast envelope:
Double membrane
Highly selective on what enters and leaves organelle
Grana/Thykloids:
Within them have photosynthetic pigment (chlorophyll)
Thykloids are where light absorption takes place (stage 1 of photosynthesis)
Stroma:
Fluid filled matrix
Synthesis of sugars (stage 2 of photosynthesis)
Within the stroma are starch grains.
Connections between thylakoids: Lamellae.
How are chloroplasts adapted to their function:
Granal membranes- Provide large surface area for attachment of chlorophyll.
Fluid of stroma possesses all the enzymes needed to make sugars in second stage of photosynthesis.
Chloroplasts contain both DNA and ribosomes so they can quickly produce proteins for photosynthesis
Endoplasmic Reticulum:
Compare structure and functions of RER AND SER.
RER:
Has ribosomes present over surfaces
Provide large surface area
For synthesis of proteins and glycoproteins
Provide pathway for the transport of materials, especially proteins throughout cell.
SER:
(Lack of ribosomes on surface of organelle)
Synthesise store and transports lipids and carbohydrates.
Describe structure and function of Golgi Apparatus:
Function: Add carbohydrates to proteins to form glycoproteins.
-Forms lysosomes
-Transport, modify and stores lipids
-Secrete carbohydrates such as those used in making cell walls.
Lysosomes:
Describe function, formation and the enzyme in lysosomes.
Formed from vesicles of Golgi apparatus.
Contains lysozymes which can hydrolyse cell walls of certain bacteria
Describe structure and function of ribosomes
Site of protein synthesis
80s - found in eukaryotic cells
70s - found in prokaryotic cells, mitochondria and chloroplasts
Describe structure and function of cell walls.
Consist of microfibrils
Consist of a number of polysaccharides eg. Cellulose
Provide mechanical strength in order to prevent the cell bursting under pressure.
Cell walls of fungi made of chitin.
Describe structure and function of vacuole:
Fluid filled sac bounded by a single
Membrane.
Makes cell turgid
May act as a temporary store of sugars and amino acids.
Pigments may colour petals to attract pollinating insects.
Compare eukaryotic and prokaryotic cell structures:
Eukaryotic:
Larger and have a nucleus bounded by a nuclear envelope
Prokaryotic:
Smaller, no nucleus, no nuclear envelope.
Structure of bacterial cell:
-Has a cell wall made of murein
-Slime capsule
Cell surface membrane containing 70s ribosomes
Circular strand of DNA
Plasmids(smaller pieces of DNA which can replicate separately)
Flagellum (locomotion)
Describe the stages of Mitosis:
Prophase:
-Chromosomes CONDENSE
- Centrioles move to poles and spindle fibres first develop
Metaphase:
Chromosomes pulled by spindle fibres to equator
Anaphase:
Centromeres divide into two
Spindle fibres pull individual chromatids to opposite poles
Telophase:
Chromosomes reach poles becoming longer and thinner. (Dissipate)
Leaving widely spread chromatin
Spindle fibres disintegrate
Cytokinesis:
Cytoplasm divides
Describe Binary fission in Prokaryotic cells:
-Circular DNA replicates, both copies attach to cell membrane
- Plasmids replicate
- Cell Membrane begins to grow in between two DNA molecules dividing cytoplasm into two.
- New cell wall forms between two molecules of DNA
-New cell wall forms between two molecules of DNA dividing original cell into two identical daughter cells each with a single copy of circular DNA and a variable number of copies of the plasmids
3 stages to cell cycle:
1: Interphase- ‘Resting stage’ / no division takes place
2: Nuclear division. Nucleus divides:
Into two (mitosis)
Into four (meiosis)
3: Division of the cytoplasm (cytokinesis) divides to form 2 cells (mitosis) and 4 cells (meiosis)
Treatments to cancer:
-Prevent DNA Replication
-Inhibit metaphase/ interference of spindle fibre formation.
-Disadvantages:
Other healthy cells get damaged.
Hair cells which are highly mitotically active are vulnerable to damage especially.
