Cells Flashcards
What do all cells contain?
- A cell-surface membrane enclosing cell contents.
- Cytoplasm.
- Genetic material, made of DNA.
What groups can cells be divided into?
Prokaryotic: Bacteria
Eukaryotic: Cells found in plants, fungi, algae and animals that have internal membranes, forming organelles
What is an organelle?
Small cellular structure in cytoplasm that has a specific function.
What are the differences between eukaryotic cells and prokaryotic cells?
- Both have ribosomes.
- Both have a cell-surface membrane.
- Prokaryotes have circular DNA whereas eukaryotes have linear DNA arranged as chromosomes.
- Eukaryotes have mitochondria whereas prokaryotes do not have mitochondria.
- Eukaryotes have membrane-bound organelles whereas prokaryotes don’t have membrane-bound organelles.
- Prokaryotes may have a capsule whereas eukaryotes do not have a capsule.
- Prokaryotes have a cell wall made of murien whereas place cells have a cell wall made of cellulose and fungal cell wall is made of chitin and animal cells do not have a cell wall.
- Prokaryotes may have plasmids whereas eukaryotes do not have plasmids.
- Eukaryotes have larger ribosomes (80S) whereas prokaryotes have smaller ribosomes (70S).
How do prokaryotes form new cells?
By binary fission.
What structures does a bacterium/prokaryote have?
DNA:
- Short, circular molecule of DNA, not associated with protein and free in the cytoplasm.
- Carries genetic codes for protein.
Cell Wall:
- Contains murein, a glycoprotein.
- Prevents osmotic lysis, rigid, strengthening.
Cytoplasm:
- Solution where many dissolved molecules are found, no membrane-bound organelles in a prokaryote.
- Site of many metabolic reactions.
Cell surface membrane:
- Phospholipid bilayer with embedded proteins.
- Controls passage of substances across exchange surfaces by passive or active transport.
Small Ribosomes:
- Small structures in cytoplasm (70S size).
- Site of protein synthesis.
Simple flagellum:
- Thin rotating fibre.
- Responsible for movement of cell.
Plasmids:
- One or more small loops of DNA, can replicate independently.
- Can pass on genetic information via conjugation to other bacteria.
Capsule:
- Extra layer outside cell wall.
- Protects from desiccation, phagocytosis and some pathogens.
How do eukaryotic cells form new cells?
By mitosis and meiosis.
What structures does a eukaryotic cell have and what are the functions?
Cell-surface membrane:
- Membrane found on cell surface and most internal organelles. Made of a phospholipid bilayer which also contains embedded proteins.
- Selectively permeable and allows cell identification.
Nucleus:
- Contains chromatin which are long, linear DNA molecules associated with just one protein. Surrounded by a nuclear envelope. Also has one or more nucleoli.
- DNA contains genetic code for making proteins and nucleolus manufactures ribosomes.
Mitochondrion:
- Oval shaped organelle surrounded by 2 membranes. Inner membrane folded and forms cristae. Fluid inside called matrix. Contains DNA like that in prokaryotes.
- Produces ATP from aerobic respiration. ATP used by cell for active processes such as active transport and protein synthesis.
Rough endoplasmic reticulum:
- A series of tubes in the cytoplasm of the cell. Appears rough due to ribosomes attached to membranes.
- Synthesis and transport of proteins through cytoplasm.
Ribosomes:
- Made of RNA and protein. Not surrounded by a membrane. Larger than in prokaryotes (80S).
- Site of protein synthesis.
Smooth endoplasmic reticulum:
- A series of tubes in the cytoplasm of the cell. No ribosomes attached.
- Synthesises and transports lipids.
Golgi apparatus:
- Stack of flattened sacs.
- Modifies proteins that are made in the cell, such as converts them to glycoproteins. Packages them into vesicles. Forms lysosomes.
Vesicles:
- Continually pinched off from the end of the sacs of golgi body.
- Used to transport proteins to the cell-surface membrane for release.
Lysosomes:
- Golgi vesicle containing hydrolytic enzymes, sometimes known as lysosomes.
- Digest unwanted material in the cell such as damaged organelles or pathogens.
What is the structure of a plant cell and functions of the organelles?
- Cell wall - Made of cellulose, which provides high tensile strength that prevents osmotic lysis.
- Vacuole - Filled with cell sap which gives rigidity.
Chloroplast - The site of photosynthesis.
What are the features and functions of chloroplasts?
Envelope - A double-membrane surrounding the chloroplast
Granum - A stack of membrane-bound discs called thylakoids. The thylakoid membranes contain chlorophyll. The membranes provide a large surface area for light absorption to maximise the rate of photosynthesis.
Stroma - Contains enzymes needed for photosynthesis and stores starch grains.
DNA - Short, circular and not associated with proteins.
What is a tissue, organ and organ system?
Tissue - A group of similar cells.
Organ - A group of tissues organised into a structure which serves a particular physiological function.
Organ system - A group of interacting, interrelated or interdependent organs forming a complex functional whole.
What are the features of a virus?
- Genetic material: either DNA or DNA
- Caspid: a protein coat
- Attachment protein: allow the virus to attach to a host cell complementary to and attach to receptors on host cell membrane.
What is magnification?
The number of times bigger the image appears compared to its actual size.
What is resolution?
The minimum distance between 2 points at which they can be seen as separate.
Describe optical microscopes.
- Use light to illuminate the specimen.
- Use glass lenses to focus the light.
- Has an eyepiece lens of fixed magnification and a selection of objective lenses of various magnifications.
- Specimens must be very thin to transmit the light.
- Light has a relatively long wavelength and so optical microscopes have a low resolution.
- Can form coloured images.
- Living specimens can be seen.
- Preparation of specimens is simple.
Contrast transmission electron microscopes and scanning electron microscopes.
Transmission:
- Beam of electrons is transferred through the specimen. The specimen must be very thin.
- Has greater resolution so smaller organelles can be observed, as well as internal details of organelles.
- Cannot form 3D images.
Scanning:
- Electrons are reflected off the surface.
- Has a lower resolution
- Does not require thin sections.
- Can have 3D images.
- Usually show the surface of the object.
Both:
- Use a beam of electrons and electromagnets.
- Black and white images only.
- Only dead specimens can be used.
- Complex preparation of specimens can result in artefacts.
What is an artefact?
Something that results from the way a specimen is prepared. They are not part of the natural specimen. It is not always easy to distinguish artefacts from cell organelles.
How do you covert millimetres to micrometers and convert micrometers to nanometers?
Millimetres —> Micrometers - X 1000
Micrometers —> Nanometers - X 1000
How would you measure something using an optical microscope?
- Measure with an eyepiece graticule.
- Calibrate against something of known length.
What the process of cell fractionation and ultracentrifugation?
1) Cells are broken open using a homogeniser. Once homogenised, cell membranes become broken which allow organelles to be released.
2) Cell debris and whole/unbroken cells are filtered off.
3) Place in a ultracentrifugation and the most dense organelle (the nucleus) will form at the bottom of the tube. The rest of the organelles would still be suspended in the supernatant.
4) The ultracentrifugation process is then repeated to separate mitochondria, and then again for ribosomes.
What conditions must tissue be kept in during organelle isolation and why?
- The tissue is kept in ice-cold, isotonic, buffer solution.
1) Cold temperature:
- Reduce enzyme activity.
- Prevents digestion of proteins, including enzymes.
2) Isotonic: Same water potential as organelles to prevent osmotic lysis of organelles.
3) Buffer:
- Maintains and controls and pH.
- Prevents the denaturation of proteins, including enzymes.
