Unit 2 - Cell Structure Flashcards
Nucleus
- Controls cell functions by controlling DNA transcription
- Controls for:
Gene Expression
Protein Synthesis
Storing DNA
Nucleolus
Site of protein synthesis and ribosome production
Cell Surface Membrane
Regulates the movement of substances in and out of the cell
Mitochondria
- Site of aerobic respiration
- Produces ATP
Chloroplast (Plants and Algae)
Provides energy for plants and algae via photosynthesis
Golgi Apparatus
Processes and packages proteins and lipids to be transported to the vesicles
Golgi Vesicles
Stores and transports lipids and proteins out of the cell via the cell membrane
Lysosomes
Contains lysozymes (hydrolytic enzymes) that digest unwanted cell parts and complex biomolecules
Hydrolytic Enzymes
- Break down macromolecules
- Membrane-bound so they don’t self digest
Ribosomes
Synthesise proteins from mRNA during translation
Rough Endoplasmic Reticulum
- Synthesizes glycoproteins
- Produces 3D structures of proteins
Smooth Endoplasmic Reticulum
- Synthesizes lipids, phospholipids and cholesterol
- Contains enzymes that detoxify harmful substances
Cell wall (Plants, Algae and Fungi)
- Provides structural support by maintaining cell shape
- Protects the cell from invading pathogens
- Made of cellulose in plants and algae
- Made of chitin in fungi
Cell Vacuole (Plants)
- Maintains osmotic pressure in the cell to stop the plant from wilting
- Store unwanted chemicals as an emergency food store
4 Main Eukaryotic Kingdoms
- Animals
- Plants
- Fungi
- Protists
Cell Fractionation
- The process where cells are broken up and their organelles are separated out
- Two stage process (homogenation and ultracentrifugation)
Homogenation
- Tissue is cut up and placed in a cold, buffered, isotonic solution
- Cells are broken up in a homogeniser (releases the organelles from the cell)
- The homogenate is filtered to remove any cell membrane
- Suspension of homogenate is placed in a test tube and centrifuged
Conditions of the Solution for Cell Fractionation
- Cold
- Isotonic
- Buffered
Why does the solution have to be cold?
- To reduce enzyme activity
- Makes sure the organelles aren’t broken down
- Why does the solution have to be isotonic?
- To prevent water being lost/gained
- Prevents the organelles from bursting/shrinking
Why does the solution have to be buffered?
- To maintain a constant pH
- Prevents enzyme activity from being impacted
- Prevents organelle structure from being altered
Ultracentrifugation
- Suspended homogenate is placed in ultracentrifuge and spun at low speed
- The densest organelles collect at the bottom where they form sediment
- The supernatant liquid is then put in another tube where it is spun at higher speeds
- The next densest organelles collect at the bottom
- Repeat process
Order of Organelle Density
- Nucleus
- Mitochondria/Chloroplast
- Endoplasmic Reticulum/Golgi Complex
- Ribosomes
How does the speed of the centrifuge impact fragment size?
- Slower speeds = larger fragments
- Faster speeds = smaller pellets
Magnification
The number of times an image is enlarged compared with the real size of the object
Magnification Equation
Size of image/Size of actual object
Resolution
The minimum distance two objects can be apart in order for them to appear as separate items
Optical (Light) Microscope
- Used for specimens above 200nm
- Specimens can be alive or dead
- Wavelength of light is longer than electron wavelength so resolution is lower
- Produces coloured images
- Used to look at whole cells, small organisms and tissues
Electron Microscope
- Used for specimens above 0.5nm
- Shorter wavelength so higher resolution
- Electrons are absorbed or deflected by molecules in the air
- Vacuum is needed so can’t be used to observe living organisms
- TEMs and SEMs
Transmission Electron Microscope (TEM)
- Beam of electrons passes through
a thin part of the specimen - Parts of the specimen absorb the electrons and make the specimen appear dark
- Parts of the specimen transmit electrons and make the specimen appear light
- Resolving power of 0.1nm
Limitations of TEMs
- Black and white image due to absorbed (dark parts) and transmitted (light parts) electrons
- Specimen has to be extremely thin
- Image may contain artefacts
Scanning Electron Microscope (SEM)
- Beam of electrons passes across the surface of the specimen and scatter along the surface
- The pattern of scattering builds up a 3D image of the specimen
- Resolving power of 20nm (lower than TEMs)
Limitations of SEMs
- Black and white image due to absorbed (dark parts) and transmitted (light parts) electrons
- Image may contain artefacts
- However the specimen doesn’t have to be thin as electrons don’t penetrate the specimen
Artefacts
Damage caused in specimen preparation and can be confused with structures within the specimen
Cell Differentiation
- The process where cells become differentiated
- Cells acquire different sub-cellular structures and change shape
Sperm Cell
- Flagellum allows cell to swim through the uterus and fallopian tube to reach the egg
- Streamline head (same reason as flagellum)
- Lots of mitochondria provide energy for movement
- Digestive enzyme in the head to infiltrate egg cell
White Blood Cells
- ## High amount of lysosomes to break down invading pathogens
Mitosis
- A form of cell division that produces genetically identical cells
- 4 stages: Prophase, Metaphase, Anaphase, Telophase
Interphase
- G1: Cell carries out metabolic functions, Proteins that cell organelles are synthesized from are produced
- S: Synthesis, DNA replicates, 2 sister chromatids form from each chromosome
- G2: Mitochondria divides and cell continues to grow
Prophase
- Chromosomes condense and become visible when stained
- Nuclear envelope disintegrates
- Nucleolus disappears
Metaphase
- Spindles form
- Chromosomes line up on the equator
- Pairs of chromatids attach to spindles by centromeres
Anaphase
Spindle fibres contract and pull chromatids by centromeres to opposite poles
Telophase
- Chromatids reach poles
- Nuclear Envelope reforms
- Nucleolus reappears
- Spindles disintegrate
- Chromosomes uncoil and become long and thin
Cytokinesis
- Replicated organelles move to opposite poles
- Cytoplasm divides
- 2 new daughter formed
Prokaryote Structural Differences
- Between 10-100 times smaller than eukaryotes
- No membrane-bound organelles
- Smaller ribosomes
- No nucleus
- Cell wall is made of murein instead of cellulose
Plasma Membrane
Regulates the movement of substances in and out of the cell (same as eukaryotes)
Mesosomes
In-foldings of the cell membrane that increase surface area for attachment of enzymes involved in respiration
Slime Capsule
- Slimy layer that prevents the cell from desiccation (drying out)
- Protects the cell against the action of a host’s digestive enzymes
Pili
Hair-like structures which
attach to other bacterial cells
Flagellum
- Tail like structure
which rotates to move the cell
Plasmids
Circular DNA
Virus
- Non cellular and border between living and non-living
- Smaller than prokaryotes
- Have nucleic acid and a capsid (protein coat)
- Some have a lipid envelope with attachment proteins on it
- All viruses are parasitic
