2.1 Cell Structure Flashcards
Describe how a light microscope works.
•Lenses focus rays of light and magnify the view of a thin slice of a specimen
•Different cellular structures absorb different amounts of wavelengths of light
•Reflected light is transmitted to the observer via the objective lens and the eyepiece
Describe how a transmission electron microscope (TEM) works.
•A high energy bean of electrons is passed through a thin slice of specimen
•The more dense of the cellular structures appear darker as they absorb more electrons
Describe how a scanning electron microscope (SEM) works.
•A beam of electrons is focused onto a specimen’s surface using electromagnetic lenses
•Electrons are then reflected off of the specimen and into a collecting device, which generates an image
Describe how a laser scanning confocal microscope works.
•A laser beam is focused onto a small area on a sample’s surface using objective lenses
•A fluorescent stain is added to the sample, which reflects the laser
•A detector then generates an image of the sample pixel by pixel.
How should field of view in microscopy be recorded?
•Draw diagram of image
•Include scale bar
•Annotate visible structures
State an equation to calculate the actual size of a structure from microscopy.
•Image size = Actual size x Magnification
Define magnification and resolution
•Magnification: the factor by which the image is larger than the actual specimen
•Resolution: the smallest separation distance at which 2 separate structures can be distinguished from one another
Why do samples need to be stained for light microscopes ?
•Coloured dyes bind to the structures
•Allows for the absorption of some wavelengths of light to produce an image with contrast.
What is differential staining ?
•Contrast between heavily and lightly stained areas, allows for distinguishing structures.
State the magnification and resolution of a optical light microscope.
•Magnification : x2000
•Resolution : 200nm
State the magnification and resolution of a TEM.
•Magnification : x500,000
•Resolution : 0.5nm
State the magnification and resolution of a SEM.
•Magnification : x500,000
•Resolution : 3-10nm
Explain how to use the eyepiece graticule and stage micrometre to measure the size of a sample’s structures.
•Place micrometre on stage to calibrate eyepiece graticule
•Line up scales on graticule and micrometre. Count how many graticule divisions are in 100µm on mictometre
•Length of 1 eyepiece division = 100µm / number of divisions
•Use calibrated values to calculate actual length of structures
Describe the structure of the nucleus.
•It is surrounded by a semipermeable double membrane called the nuclear envelope
•Nuclear pores allow substances to enter/exit
•Dense nucleolus made of RNA and proteins, assembles ribosomes.
Describe the function of the nucleus
•Contains DNA coiled around chromatin into chromasones
•Controls cellular processes: gene expression (specialisation and site of mRNA transcription), mitosis, semiconservative replication
Describe the structure and function of the endoplasmic reticulum (ER)
•Rough ER: many ribosomes attached for protein synthesis and transport
•Smooth ER: lipid synthesis
What is the cisternae?
•The network of tubules and flattened sacs that extends from cell membrane and connects to nuclear envelope
•What makes up the golgi and ERs
Describe the structure and function of the golgi apparatus
•A stack of membrane bound flattened sacs.
•It Modifies and packages proteins/lipids for export
Describe the structure and function of ribosomes
•It is formed of protein and rRNA
•They have a large subunit which joins to amino acids and a small subunit with an mRNA binding site
Describe the relationship between the organelles involved in the production and secretion of proteins.
•The ribosomes that synthesise proteins are attached to the rER
•The golgi apparatus which modifies proteins for secretion aligns with the rER.
Describe the structure of a mitochondrion
It is surrounded by a double membrane
It has a folded inner membrane called the cristae
Describe the structure of a chloroplast
Contains flattened discs called thylakoids, which contain chlorophyll
Thylakoids are organised into grana
Intergranal lamellae are tubes that attach thylakoids within grana
State the function of mitochondria and chloroplasts
Mitochondria: the site if aerobic respiration to produce ATP
Chloroplasts: the site of photosynthesis to convert solar energy into chemical energy
Describe the structure and function of a lysosome
A single membrane sac that contains digestive hydrolase enzymes.
Describe the structure and function of a plant cell wall
Made of cellulose microfibrils
Plasmodesmata between adjacent cells forms apoplast pathway
What are bacterial and fungal cell walls made of ?
Bacteria: peptidoglycan
Fungi: Chitin
Describe the structure and function of centrioles.
A group of microtubules
Centrioles migrate to opposite poles of the cell during prophase and spindle fibres form between them
Describe the structure and function of the cell surface membrane
Structure:
‘Fluid mosaic’ phospholipid bilayer
Extrinsic proteins (exterior) and intrinsic proteins (through) embedded
Function: Separates cytoplasm for extracellular environment
Selectively permeable to regulate the transport of substances
Involved in cell signalling and recognition
Explain the role of cholesterol, glycoproteins and glycolipids in the cell-surface membrane.
Cholesterol: connects phospholipids, increasing packing. Increases fluidity at low temps decreases at higher temps
Glycoproteins: cell signalling, cell recognition (antigens) and binding cells together
Glycolipids: cell signalling and recognition
Describe the structure and function of flagella
Hollow tube made of the protein flegellin
Rotates to propel cell
Describe the structure and function of cilia
Hairlike protrusions on eukaryotic cells
They move back and forth to sweep foreign substances (eg dust/pathogens) and to enable some movement
Why is the cytoskeleton important?
Provides mechanical strength
Aids transport within cells
Enables cell movement
What are the differences between prokaryotic and eukaryotic cells
Eukaryotic are larger
Prokaryotic lack membrane bound organelles + nucleus
Eukaryotic have linear chromosomes with histones
Prokaryotic have smaller ribosomes
Prokaryotic divide by binary fission not mitosis/meiosis
Prokaryotic cell wall is made of peptidoglycan not cellulose/chitin
Prokaryotic always have capsule and sometimes cytoskeleton
Eukaryotic have no capsule and always cytoskeleton
