Section 2: Cell structure Flashcards
What is the structure and function of the cell-surface membrane?
- Phospholipid bilayer with embedded proteins
- Selectively permeable - controls passage of substances
- Barrier between internal and external environments
What is the structure and function of the nucleus?
- Nuclear envelope, nuclear pores, nucleolus, DNA/ chromatin
- Controls cell activities through transcription of mRNA
- Nuclear pores allows substances to move
- Nucleolus makes ribosomes which are made of proteins and ribosomal RNA
What is the structure and function of the mitochondria?
- Double membrane - inner membrane folded to form cristae
- Matrix containing 70S ribosomes, small circular DNA and enzymes
- Aerobic respiration producing ATP
What is the structure and function of the Golgi Apparatus?
- Fluid filled membrane bound sacs with vesicles at the edge
- Receives proteins from RER
- Modifies/ processes proteins e.g add carbohydrates
- Packages into vesicles
- Makes lysosomes
What is the structure and function of lysosomes?
- Type of golgi vesicle containing lysozymes
- Breaks down/ hydrolyse pathogens and worn out cell components
What is the structure and function of ribosomes?
- Float free in cytoplasm or bound to RER - not membrane bound
- Made from 1 large and 1 small subunit
- Site of protein synthesis - translation
What is the structure and function of the RER?
- Ribosomes bound by membranes
- Folds polypeptides to secondary/ tertiary structure
- Packages to vesicles, transport to the Golgi
What is the structure and function of SER?
- Similar to RER but without ribosomes
- Synthesises and processes lipids
What is the structure and function of chloroplasts?
- Thylakoid membranes are stacked up to form grana which are linked by lamellae
- These sit in the stroma and are surrounded by a double membrane
- Also contains starch granules and circular DNA
- Chlorophyll absorbs light for photosynthesis
What is the structure and function of the cell walls?
- Made of cellulose in plants and algae and chitin in fungi
- Rigid structure surrounding plant and fungi.
- Prevents the cell changing shape and bursting lysis
What is the structure and function of the cell vacuole?
- Contains cell sap - weak solution of sugars and salts
- Surrounding membrane is called the tonoplast
- Maintains pressure in the cell
- Stores/ isolates unwanted chemicals in the cell
What is a tissue?
- Group of organised cells, joined together to perform a particular function
What is an organ and organ system?
- Group of organised tissues, working together to perform a particular function
- Group of organised organs, working together to perform a particular function
What are the differences between prokaryotic and eukaryotic cells?
- Prokaryotic = no membrane bound organelles
- Prokaryotic = no nucleus/ contains free floating DNA
- Prokaryotic DNA = circular and not associated with proteins. Eukaryotic is
- Prokaryotic cell walls = murein and peptidoglycan. Eukaryotic = cellulose
- Prokaryotic = smaller 70s ribosomes, Eukaryotic = 80S
- Prokaryotic = plasmid, capsule, flagella
What are the differences between prokaryotic and eukaryotic cells?
- Prokaryotic = no membrane bound organelles
- Prokaryotic = no nucleus/ contains free floating DNA
- Prokaryotic DNA = circular and not associated with proteins. Eukaryotic is
- Prokaryotic cell walls = murein and peptidoglycan. Eukaryotic = cellulose
- Prokaryotic = smaller 70s ribosomes, Eukaryotic = 80S
- Prokaryotic = plasmid, capsule, flagella
What are the different structures in a virus?
- Attachment proteins
- Capsid
- RNA
- Reverse Transcriptase
- Lipid envelope
How do you use an optical microscope and what is its resolution and magnification?
- Use light to form 2D image
- Visible light longer wavelength
- Magnification = x1500
- Resolution = 0.2 micrometres
Advantages of using an optical microscope:
- Can see living organisms
- Staining process less complicated and cheaper
Disadvantages of using an optical microscope?
- 2D image
- Only on thin specimens
- Low resolution - can’t see internal structures
- Low magnification
How to use a scanning electron microscope and what is its magnification and resolution:
- Forms 3D image
- Beam of electrons scan surface, knocking off electrons from the specimen and are gathered in a cathode ray tube to form an image
- Electrons have a shorter wavelength = 0.2nm
- High mag x1500000
Advantages of using TEM or SEM:
- SEM = 3D image
- High resolution
- High magnification
- SEM = on thick specimens
What are the disadvantages of using SEM:
- Vacuum, can’t see living organisms
- Lower resolution than TEM
How to use a TEM and what is its magnification and resolution?
- Electromagnets to focus a beam of electrons onto a specimen
- More dense areas = more absorbed
- Electrons have shorter wavelength, resolution = 0.2nm
- High mag = x1500000
How to use a TEM and what is its magnification and resolution?
- Electromagnets to focus a beam of electrons onto a specimen
- More dense areas = more absorbed
- Electrons have shorter wavelength, resolution = 0.2nm
- High mag = x1500000
What is magnification?
Magnification - how much bigger the image of a sample is compared to the real size,
measured by
Magnification =
Size of image /
Size of real object
What is resolution?
Resolution - how well distinguished an image is between 2 points; shows amount of detail;
limited by wavelength of radiation used
How do you measure the size of an object viewed with an optical microscope?
- Line up eyepiece graticule with stage
micrometer - Use stage micrometer to calculate the size
of divisions on eyepiece graticule at a
particular magnification - Take the micrometer away and use the
graticule to measure how many divisions
make up the object - Calculate the size of the object by multiplying the number of divisions by the size of
division - Recalibrate eyepiece graticule at different magnifications
How do you prepare a temporary mount?
- Use tweezers to place a thin section of specimen e.g. tissue on a water drop on a
microscope slide - Add a drop of a stain e.g. iodine in potassium iodide solution used to stain starch grains in
plant cells - Add a cover slip by carefully tilting and lowering it, trying not to get any air bubbles
What are the main stages in cell centrifugation?
- Homogenise
- Filter
- Ultracentrifuge
