2.1 Eukaryotic and prokaryotic cell structure + function Flashcards
What is the unifying concept of cell theory?
1) Cells - smallest unit of life.
2) All cells derived from division of pre-existing cells.
3) Within cells are the sites of all chem reactions of life.
What is the meaning of cell theory?
- Cells fundamental unit of structure, function + organisation in all living organisms.
What is the definition of a unicellular organism?
- Organism composed of a single cell.
What are cells organised into in complex organisms?
- Tissues, organs + organ systems.
What is the definition of a multicellular organism?
- Organism composed of many cells.
- Cells differentiate to become arranged into tissues, organs + systems that carry out different functions.
What is the process of differentiation?
- Developmental process - structure of cells in a multicellular organism specialise, becoming adapted for a specific function.
What happens to specialised cells?
- No longer able to divide.
- Cells show great variety in shape + structure.
What is the definition of a tissue?
- Group of cells w common origin + similar structure that work together to perform a single function.
What is an example of an animal tissue and an example of a plant tissue?
- Animal tissue –> blood.
- Plant tissue –> xylem.
What is the definition of an organ?
- Structure made of more than one type of tissue, that work together to perform a specific function.
What is the definition of an organ system?
- A group of organs + tissues that perform a particular function.
What is an example of an organ system?
- Circulatory system –> heart, together with blood vessels + blood.
What is the definition of a prokaryotic cell?
- Microorganisms, typically unicellular + have fundamentally different structure to eukaryotes.
What are the examples of prokaryotes?
- Bacteria + Cyanobacteria (photosynthetic bacteria).
What are the distinctive features of prokaryotes?
- Size –> exceedingly small - about size of ribosomes/chloroplasts in eukaryotic cells.
- Absence of (membrane-bound) nucleus.
Do prokaryotic cells have a membrane-bound nucleus?
- Single circular DNA molecule molecule (nucleoid).
- Unlike eukaryotic, DNA in nucleoid is not associated w protein.
What is the definition of a nucleoid?
- Circular DNA molecule found in prokaryotic cells.
- Don’t refer to as chromosome - the DNA in neither linear nor associated w histones.
Which structures are found in all prokaryotic cells?
- Cytoplasm, plasma membrane, ribosomes, nucleoid, cell wall.
Which two structures are only found in some prokaryotic cells?
Pili + Flagella.
What are plasmids + what is their function?
- Circular DNA molecules (in addition to nucleoid).
- usually only contain a few genes - usually conferring resistance to antibiotics.
What are 70s ribosomes?
- Involved in protein synthesis, but smaller than 80s ribosomes in eukaryotic cells.
What is found in the cytoplasm of prokaryotic cells?
- Lack of membrane-bound organelles.
- No mitochondria, chloroplasts, golgi apparatus or endoplasmic reticulum.
What are the functions of cell walls in all prokaryotic cells?
- Protects cells from rupture caused by osmosis + possible harm from other organisms.
What does a mesosome look like?
- In-tuckings of the cell membrane.
What actually is a mesosome?
- An artefact.
What is an artefact?
- Part of specimen viewed under microscope that wasn’t part of original cell.
- Damage caused by processing tissue for examination.
What are cell walls made up from in prokaryotic cells?
- Not cellulose as plant cells, instead they are PEPTIDOGLYCAN.
What is the function of Pili?
- Enable attachment to surfaces + other bacteria.
What is the function of Flagella?
- Bring about movement of the bacterium.
What is peptidoglycan in cell walls made of?
- Polymers of amino acids + sugars.
How are gram positive cell walls compromised and how does this affect staining?
- Thick walls made almost entirely of peptidoglycan.
- Wall becomes purple when stained w crystal violet.
How are gram negative walls compromised and how does this affect staining?
- Thin peptidoglycan walls w additional outer-membrane w high lipid content.
- Prevents crystal purple from getting to cell wall, so bacteria do not become purple.
What is the outer-layer of gram negative bacteria made of?
- Lipid + polysaccharide.
What happens in stage 1 of gram staining?
- Bacteria in an air-dried smear on a microscope slide appears colourless.
What happens in stage 2 of gram staining?
- Smear is treated w crystal violet.
- cells all appear violet when stain is washed from the slide.
What happens in stage 3 of gram staining?
- Smear is flooded w Lugol’s iodine (mordent treatment to combine dye to bacteria).
What happens in stage 4 of gram staining?
- Smear now treated w decolourising solution of acetone + alcohol.
- Removes violet dye from cells not reacted.
- Gram positive bacteria remain purple.
What happens in stage 5 of gram staining?
- Red dye Safranin is added as counter-stain.
- Taken up by colourless bacteria of the treatment smear.
What are the final results of gram staining?
- Gram positive –> Purple.
- Gram negative –> Red.
When and who discovered gram staining?
- The Dane, Hanz Gram.
- 1884.
Why was gram staining devised?
- To differentiate between the two types of bacteria.
How does antibiotics affect gram positive + gram negative bacteria? and why does this difference happen?
- Gram positive - susceptible to penicillin.
- Gram negative - resistant to many types of antibiotics.
- Outer, lipid-rich membrane of gn bacteria is relatively impermeable to antibiotics + antigens are hidden.
What is an organelle?
- A structure within cytoplasm of a eukaryotic cell that performs a discrete function.
Which organelles are membrane-bound in prokaryotic cells?
- All with the exception of ribosomes.
What is the solution around organelles called?
- Aqueous solution of chemicals - cytosol.
What are the cytosol and organelles contained in in eukaryotic cells?
- Cell surface membrane.
How have images of the ultrastructure of eukaryotic cells been made?
- With TEM’s (Transmission Electron Micrographs).
What is the role and structure of the nucleus in eukaryotic cells?
- Role in protein synthesis.
- Largest organelle in eukaryotic cell (10-20 μm diameter).
- Surrounded by double nuclear membrane w pores.
What is the size and purpose of nuclear pores in eukaryotic cells?
- 100nm.
- Allow movement of molecules between cytoplasm + nucleus e.g. mRNA.
What are the chromosomes in nuclei in eukaryotic cells?
- Each chromosome contains long strand DNA wound around beads of histone (type of protein).
When can chromosomes be seen in eukaryotic cells?
- Only visible w light microscope when nucleus divides.
- At other times, appear dispersed as a diffuse network, called chromatin.
What is a nucleoli?
- Single nucleolus, present in nucleus.
- Rounded, dark-staining bodies - sites of ribosome synthesis.
Which parts of the nucleus can only be seen when stained with certain dyes?
- Chromatin, chromosomes + the nucleolus.
What are some examples of eukaryotic cells that don’t contain one nucleus?
- Mature RBCs (mammals) - 0.
- Mature sieve elements in phloem of flowering plants - 0.
- Voluntary muscle cells + mycelia of fungi - both contain many nuclei.
What are features of mitochondria?
- Rod-shaped, 0.5-1.5μm diameter, 3.0-10.0μm long.
- Each has double membrane.
What are the features of the double membrane of the mitochondria in eukaryotic cells?
- Outer membrane, smooth boundary.
- Inner membrane, infolded to form cristae
What is in the middle of the mitochondria?
- Aqueous solution of metabolites + enzymes, called the matrix.
- Small circular molecules of DNA in matrix.
What do chloroplasts look like?
- Biconvex shape.
- 4-10μm long + 2-3μm wide.
Where are chloroplasts found?
- Cells of green plants + photosynthetic protoctists.
- Plants –> found in mesophyll.
What are chlororplasts?
- The site of photosynthesis.
What are the two layers of the double membrane of chloroplasts?
- Outer - smooth continuous boundary.
- Inner - in-tucked to form system of of branching membranes - lamellae or thylakoids.
- These are arranged in flattened circular piles called grana (singular granum).
What is located in the stroma of chloroplasts?
- Pigments including chlorophyll.
- Lots of grana.
- branching membranes in aqueous solution w enzymes + starch grains.
What are plastids?
- Organelles found in plant cells but not animal cells.
What are amyoplasts?
- Colourless plastids in which starch is stored.
What are chromoplasts?
- Coloured plastids, containing non-photosynthetic pigments.
What are ribosomes?
- Site of protein synthesis.
How is the size of a ribosome calculated?
- Recorded in Svedberg units.
- Measure of rate of sedimentation during centrifugation under standardised conditions.
- Eukaryotic have sedimentation rate of 80S.
What are ribosomes made up of?
- Two sub-units + don’t have membranes.
- Consists of protein + Nucleic acid (RNA).
Where are ribosomes found in cells?
- Found free in cytoplasm + also bound to ER to form rough ER.
What is endoplasmic reticulum?
- Consists of networks of folded single membranes forming interconnected sheets, tubes or sacs.
What is the rough endoplasmic reticulum and where is it found in eukaryotic cells?
- Continuous outer membrane surrounding nucleus.
- Develops tertiary + quaternary structures of proteins.
- Links AAs to form polypeptide chains.
What is the definition of a vesicle?
- Small, spherical organelle bounded by a single membrane - used to store + transport substances around cell.
What is the smooth endoplasmic reticulum and where is it found in eukaryotic cells?
- Not near nucleus + no ribosomes.
- Synthesises lipids, phospholipids + steroids.
What happens in the smooth ER in the cytoplasm of voluntary muscle fibres?
- Special type of smooth ER, stores calcium ions - essential in contraction of muscle fibres.
What is the Golgi apparatus?
- Stack of membranous disks called cisternae.
- One side is formed by fusion of vesicles from rough ER.
- Other side, vesicles are formed + pinched off.
What cells are Golgi apparatus most common in?
- Metabolically active - sort, modify + package polymers for secretion or use within cell.
What are lysosomes?
- Small spherical vesicles bound by single membrane.
- contain mix of 50 hydrolytic enzymes produced by RER + modified by GA.
What is the function of lysosomes?
- Breakdown of imported food vacuoles, old organelles + harmful bacteria.
How are centrioles formed?
- Microtubules of globular proteins called tubulin form network of hollow cylinders.
- These form centrioles.
How do centrioles occur?
- Occur in pairs.
- Normally lie at right angles right outside nucleus.
- Each is made of 9 bundles of microtubules.
- During cell division centrioles move apart creating spindle.
What are plant cell walls made of?
- Long, straight fibres of cellulose held together by hydrogen bonds.
How do plant cell walls protect the cell?
- Cellulose bundles at diff directions prevent stretching.
- Prevents bursting in dilute solutions.
What is the apoplast pathway in plant cell walls?
- Spaces between bundles of cellulose - allow movement of water from cell wall to cell wall.
What is the middle lamella?
- First boundary between cells during cell division - gel-like layer of calcium pectate.
- ER from parent cell gets trapped when cellulose is laid down forming plasmodesmata.
What is the definition of plasmodesmata?
- Cytoplasmic connections between plant cells through gaps in cell walls.
- Part of symplast pathway.
What is a permanent vacuole in plant cells?
- Fluid-filled + takes up bulk of cell.
- Presses cytoplasm + cell membrane against cell wall.
- Surrounded by tonoplast.
What is the tonoplast?
- Membrane surrounding vacuole.
- Barrier between fluid contents of vacuole + cytoplasm.
What are the different parts of a compound light microscope called?
- Eyepiece lens.
- Nosepiece.
- Objective lens.
- Stage.
- Condenser.
- Coarse focus.
- Fine focus.
- Built-in light source.
What is the purpose of the nosepiece on a compound light microscope?
- It is turned and clicks into different objective lenses.
What are the powers of the objective lenses on a compound light microscope?
- 4x (low).
- 10x (medium).
- 100x (high).
What is temporary preparation of a sample for viewing in a compound light microscope?
- Placing tissue on glass slide, cover w water-based liquid to stop it from drying out + put thin coverslip over.
What is permanent preparation of a sample for viewing in a compound light microscope?
- Water removed from tissue + replaced by firmer substance. Coverslip held in place by resin.
Why is it important to stain cells when viewing them under a compound light microscope?
- Cells translucent ∴ must use chemicals to react + see cell components.
What is digital microscopy?
- Attach microscope coupler or eyepiece adaptor to appropriate camera.
- Can be viewed on VDU monitor or can be printed.
What is the definition of magnification?
- Extent to which an object has been enlarged by a microscope in a drawing or photograph.
What is the magnification equation?
- M=I/A.
What is the definition of resolution?
- Ability to distinguish between 2 points that are very close together.
What is the resolution in a light microscope and an electron microscope?
- Light –> 2μm (2000nm).
- Electron –> 5nm.
How does a transmission electron microscope work?
- Electron beam passed through extremely thin section of material.
- Structures stain w heavy metal ions, making them electron opaque.
- These then look dark on image.
What can be seen on a transmission electron micrograph that cannot be seen through a light microscope?
- Cell ultrastructure.
What does Eukaryotic mean?
- True nucleus.
What does prokaryotic mean?
- Before the nucleus.
