Cells and Cell structure Flashcards
Advantages of using a light microscope:
- Easy to use (used in school settings)
- Cheap
Disadvantages of light microscope:
- Not very high magnification and resolution
Why does an electron microscope have a higher resolution than a light microscope?
Electrons have a shorter wavelength than visible light
How does a TEM work?
- Directs electrons through a thin specimen
- Electrons transmit through, get caught by detectors which create a 2D image of specimen
Advantages of a TEM:
- Very high resolution
- 2D images of thin slices
Disadvantages of TEM:
- High energy electron beam can cause radiation damage
- Complex staining method
- Artefacts present
How does a SEM work?
Directs electrons at a specimen, electrons bounce off and are captured by detectors which allows a 3D image to be formed
Advantages of a SEM:
- Images in 3D
- Best for larger samples
Disadvantages of a SEM:
- Samples have to be coated which can change natural appearance and composition
- Lower resolution than TEM
What is the difference between magnification and resolution?
Magnification is how much bigger the image is than the specimen while resolution is how well a microscope distinguishes between two points that are close together
What is cell fractionation?
Process by which cells are broken up and their organelles separated - based on differing masses
Has 2 steps: Homogenisation and Ultra-centrifugation
What are the 3 conditions for Cell fractionations and why are they used?
- Cold - Reduced kinetic energy which reduces rate of enzyme activity that could break down organelles
- Isotonic conditions - Prevents organelles from bursting or shrinking from osmosis
- Buffered solution - Maintains a constant pH so proteins don’t denature
What is homogenisation?
Breaking up cells to release organelles
What happens during homogenisation?
Homogeniser used to break up cells - producing homogenate
Filtered to remove complete cells and debris, leaving only free organelles
What is ultracentrifugation?
Filtrate from homogenation placed in ultracentrifuge and spun at a high speed
What happens in ultracentrifugation?
- Heaviest organelles forced to the bottom forming thin pellet
- Fluid at top(supernatant) is removed
- Supernatant then spun at a higher speed to gain next heaviest organelles in a pellet
Process is repeated
What is the order of organelles from most to least heavy?
Nuclei, Chloroplasts, Mitochondria, Lysosomes, Er, Ribosomes
What is the cell surface(plasma) membrane?
Membrane found on surface of animal cells and just inside cell wall of other cells.
Made mainly of lipids and proteins
What is the function of the cell surface(plasma) membrane?
Regulates movement of substances in and out of cell. Also has receptor molecules which allow it to respond to chemicals such as hormones
What is the nucleus?
Large organelle surrounded by nuclear envelope with many pores.
Nucleus contains chromosomes and one or more structures called the nucleolus.
Chromatins used to make chromosomes
What is the function of a nucleus?
Controls the cell’s activities by controlling transcription of DNA.
DNA contains instructions to make proteins.
Pores allow substances to move between nucleus and cytoplasm.
Nucleolus makes ribosomes.
What is a mitochondrion?(structure)
Have a double membrane - inner folded to form structures called cristae.
Inside is called the matrix which contains enzymes involved in respiration.
What is the function of mitochondria?
Site of aerobic respiration where ATP is produced. Found in large numbers in cells where lots of energy is required.
What is a chloroplast?(structure)
Small flattened structure found in plant and algal cells surrounded by two membranes.
Have thylakoid membranes which are stacked to form grana.
Grana linked together by lamellae
Lamellae are thin, flat pieces of thylakoid membrane
What is the function of the chloroplast?
The site where photosynthesis takes place.
Some parts of photosynthesis happen in grana, others in the stroma.
What is the golgi apparatus?
group of fluid-filled, membrane-bound flattened sacs. Vesicles often seen at edges of sacs.
What is the function of the golgi apparatus?
Processes and packages new lipids and proteins.
Also makes lysosomes.
What is a Golgi vesicle?
Small fluid filled sac in cytoplasm, surrounded by a membrane and produced by Golgi apparatus.
What is the function of a Golgi vesicle?
Stores lipids and proteins made by the Golgi apparatus and transports them out of the cell
What is a Lysosome?
Round organelle surrounded by a membrane, with no clear internal structure
What is the function of a Lysosome?
Contains hydrolytic enzymes.
These enzymes can be used to digest invading cells or break down worn out components of the cell.
What is a ribosome?
Small organelle that floats free in cytoplasm or attached to RER. Made up of proteins and RNA.
What is the function of a ribosome?
site where proteins are made
What is a Rough Endoplasmic Reticulum RER?
System of membranes closing a fluid-filled space. Surface covered in ribosomes.
What is the function of an RER?
Folds and processes proteins that have been made by ribosomes
What is a Smooth Endoplasmic Reticulum SER?
System of membranes closing a fluid-filled space. No ribosomes on surface
What is the function of an SER?
Synthesises and processes lipids
What is the cell wall?
Rigid structure that surrounds cells in plants, algae and fungi.
What is the cell wall made of in plants and algae?
Cellulose
What is the cell wall made of in fungi?
Chitin
What is the cell wall made of in prokaryotic cells?
Murein - glycoprotein
What is the function of cell wall?
Supports cells and prevents them from changing shape
What is the cell vacuole?
Membrane-bound organelle found in cytoplasm of plant cells.
Contains cell sap (weak solution of sugar and salts).
Surrounding membrane called the tonoplast.
What is the function of the cell vacuole?
Helps maintain pressure inside cell and keep cell rigid.
Stops plant from wilting.
Also involved in isolation of unwanted chemicals inside the cell
What is the flagella? (prokaryotic)
Long hair-like structure that rotates to make the cell move
What is the slime capsule? (prokaryotic)
Helps protect bacteria from attacks by cells of the immune system
What is the cell wall? (prokaryotic)
Supports cell and prevents from changing shape. Made from polymer called murein. This is a glycoprotein.
What is the cell membrane? (prokaryotic)
Made of lipids and proteins. Controls movement of substances in and out of cell.
What is the cytoplasm? (prokaryotic)
Has no membrane-bound organelles.
Has smaller ribosomes than eukaryotic
What is the circular DNA? (prokaryotic)
DNA that floats freely in the cytoplasm.
Present as one long coiled-up strand.
Not attached to any histone proteins.
What is a plasmid? (prokaryotic)
Small loops of DNA that aren’t part of the main circular DNA molecule.
Contains genes for something like antibiotic resistance and can be passed between prokaryotes
What is the size of ribosomes in Eukaryotic cells?
80S
What is the size of ribosomes in Prokaryotic cells?
70S
