2.1.1 Cell Structure Flashcards
What are the pros and cons of a light microscope?
Pros:
- Specimens can be alive or dead
- Natural colour
- Portable and easy to use
- Can see living processes
Cons:
- Long wavelength
- Low magnification
- Poor resolution
- 2D
What are the pros and cons of transmission electron microscopes (TEMs)?
Pros:
- Electrons instead of light
- Shorter wavelength
- High magnification
- High resolution
- Good detail
Cons:
- 2D
- Specimens must be dead (cut thin, in a vacuum)
- Black and white only
- Expensive
What are the pros and cons of scanning electron microscopes (SEMs)?
Pros:
- Electrons instead of light
- High magnification
- High resolution
- Good detail
- 3D
Cons:
- Specimens must be dead
- Black and white only
- Expensive
What is the difference between TEMs and SEMs?
TEMs - electrons pass through the specimen
SEMs - electrons bounce of the surface of the specimen
What are the pros of laser scanning confocal microscopes?
- Laser light used
- High resolution
- 3D
What are the resolutions and magnifications of light microscopes, SEMs and TEMs?
Light - x1500, 200nm
SEM - x100,000, 0.2nm
TEM - x500,000, 0.02nm
What are dry mounts?
- Thin slices or whole specimens
- Just coverslip placed on top
What are wet mounts?
- Water is added to specimen before lowering coverslip
What are squash slides?
- Wet mounts which have had the coverslip pushed down to squash sample
- Thin layer to enable light to pass through
E.g. root tip
What are smear slides?
- Edge of another slide smears sample across the slide
- Creates a thin, smooth, evenly coated specimen
- Coverslip placed on top
E.g. blood cells
What is the process of preparing a specimen?
- Fixing
- Sectioning
- Staining
- Mounting
What is the eyepiece graticule?
- A scaled used to measure the size of objects you are viewing under a microscope
- When the objective lens and magnification is changed, the eyepiece must be calibrated
How do you calibrate an eyepiece graticule?
- Line up the stage micrometer and the eyepiece graticule whilst looking through the eyepiece
- Count how many divisions on the eyepiece graticule fit into one division on the micrometer scale
- Divide the micrometer number by the number of eyepiece graticule divisions
Why is staining used?
- To increase contrast so cells become visible and distinguishable
- Living cells are normally colourless and transparent so they have a low magnification and resolution
What is an example of a stain?
Methylene blue - all purpose, positively charged
What is differential staining?
A technique which involves many chemical stains being used to stain different parts of a cell different colours
What is gram staining and how does it work?
- A type of differential staining using crystal violet and safranin
- Crystal violet is added and gram positive bacteria appear blue/purple as thicker peptidoglycan cell wall retains the stain
- Gram negative bacteria don’t absorb it as they have a thinner peptidoglycan cell wall so safranin is used as a counter stain turning them red
What are the rules of biological drawings?
- Draw in a sharp pencil
- Title the diagram
- State the magnification
- No shading
- Smooth, continuous lines
- Annotate cell components, cells and sections of tissue visible
- white and unlined paper
- Labels should be parallel to top of page with a ruler
- Labels shouldn’t cross and have no arrowheads
- Proportions must be correct
What are the two magnification formulae?
Magnification = size of image/size of real object
Magnification = eyepiece magnification x objective magnification
What is magnification?
Measure of how many times larger the image is compared to the object
What is resolution?
Minimum distance between two objects in which they can still be viewed as separate (determined by wavelength)
What are eukaryotic cells?
Cells that contain membrane bound organelles
What is the nucleus?
- Site of DNA replication and transcription
- Contains genetic code for each cell
- Surrounded by a nuclear envelope (double membrane)
- Outer membrane is continuous with the RER
- Pores allow mRNA and ribosomes out and nutrients and hormones in
- Chromosomes are in a loosely coiled state (chromatin) when cell is not dividing
- The nucleolus is the site of ribosome synthesis
What is the rough endoplasmic reticulum?
- Intracellular transport system made up of extensive membranes present within cytoplasm
- Studded with ribosomes
- Large SA for ribsomes
- Ribosomes make proteins which are then transported within the ER’s cisternae
What is the smooth endoplasmic reticulum?
- Contains enzymes involved with lipid metabolism (synthesis of lipids/phospholipids and synthesis of cholesterol)
- Storage site for calcium in skeletal muscle cells
- Involved with absorption, synthesis and transport of lipids from the gut
What is the golgi apparatus?
- A series of tightly packed, membrane-bound, flattened sacs (cisternae)
- Collects and processes proteins
- Adding sugar makes glycoproteins and adding lipids makes lipoproteins
- Made from vesicles budded (from ER) which fuse at forming face
- Vesicles bud off from maturing face to go to surface membrane for secretion or to be stored in the cell
What is the plasma membrane?
- Has a trilaminar appearance
- Selectively permeable
- Controls entry and exit of materials
- Made of phospholipid bilayer
What is the vacuole?
- Large fluid filled sac
- Surrounded by a membrane called the tonoplast
- Only plant cells have a permanent vacuole
- Filled with water and solutes
- Provides support by creating a pressure potential through osmosis
- Pressure means cells become turgid
What are the mitochondria?
- Rod like structures with a double membrane
- The inner membrane is highly folded to form cristae which project into the matrix
- Completes the later stages of aerobic respiration and synthesizes ATP
- Self replicating and abundant in metabolically active cells
- DNA loop codes for enzymes needed for respiration
What is the chloroplast?
- Organelle only found in plant cells
- Surrounded by a double membrane
- Inner membrane is continuous with thylakoids which run through stroma
- Thylakoids are stacked (grana)
- Site of photosynthesis
- Grana trap light energy used to fix carbon dioxide in the stroma
- Stroma contain enzymes for photosynthesis
What are the ribosomes?
- Made of protein and rRNA
- Site of protein synthesis
- Two sizes (70s is smaller ribosome found in prokaryotes and 80s is a large ribosome found in eukaryotes)
- Attached to RER or free in the cytoplasm
What are the lysosomes?
- Contain powerful hydrolytic enzymes for hydrolysis
- Single membrane
- Enzymes are kept separate from rest of the cell
- Role is to destroy damaged cells and organelles
- Present in white blood cells and acrosome of sperm head in large numbers
What are the cilia?
- Membranous cellular extensions
- Move in a wave like manner
- Contain microtubules and are formed from centrioles
What is the centriole?
- Two bundles of microtubules at 90 degrees to each other
- Present just outside the nucleus
- Triplets of microtubules form a ring
- Microtubules are made from tubulin
- Produce spindle fibres which attach to centromere of chromosome in cell division
- Involved in the formation of cilia
What is the cell wall?
- High tensile strength to prevent the cell from bursting when turgid
- Maintains cell shape
- Contributes to structural strength and support of plant
- Freely permeable
- Cellulose in plants
- Chitin in fungi
- Peptidoglycan in prokaryotes
What is the flagella?
- A whip like structure
- Aids mobility
How do the organelles produce and secrete proteins?
- Nucleus contains DNA for protein synthesis
- DNA copied into mRNA which leaves nucleus
- Proteins are made by the ribosomes of the RER
- Transport vesicles bud off from the RER and travel to the forming face of the golgi body
- Material is modified/processed
- Vesicles bud off from the maturing face of the golgi body
- Vesicle either transport material within cell to form cellular structures or fuse with the cell membrane to export contents in exocytosis
What is the importance of the cytoskeleton?
- Network of protein structures (microfilaments, intermediate filaments and microtubules) in the cytoplasm
- Provides cellular support
- Involved in movement and cell division
What are the microtubules?
- The largest cytoskeleton fibres
- Made of tubulin
- Can grow or shrink by adding dimers
- Form the track along which motor proteins walk and drag organelles
- Form the spindle before a cell divides, which enable the chromosomes to be moved
- Make up the cilia, undulipodia and centrioles
What are the microfilaments?
- Made of actin
- Give support and mechanical strength
- Keep cell’s shape stable
- Allow cell movement
What are the intermediate filaments?
- Prevent collisions
- Maintain position of organelles in cytoplasm
- Anchor the nucleus within the cytoplasm
- Extend between cells for cell signalling
What are the motor proteins?
- Myosins, kinesins and dyneins
- Drag substances around the cell along the microtubules
What are prokaryotic cells?
Cells that have no membrane bound organelles
What structures are always present in a prokaryotic cell?
- Cytoplasm
- Plasma membrane
- Cell wall
- Circular loop of DNA
- Ribosomes
How is a prokaryotic cell different to a eukaryotic cell?
- Cells are smaller
- DNA is not contained with a nucleus
- Smaller ribosomes
- Capsule prevents bacteria from desiccating and protects bacteria from hosts immune system
