Topic 2.1 - Cells Flashcards
Includes cell structure, microscopy, transport across membranes and mitosis
Describe how you convert cm → mm → μm → nm & vice versa
Define Magnification
How many times bigger the image is than the specimen (object)
Define Resolution
Minimum distance apart that two objects can be in order for them to appear as separate items
State the formula used to work out magnification
Describe how optical (light) microscopes work
Light from bulb travels through condenser lens, then specimen, up through objective lens and through eyepiece lens into your eye
State the maximum resolution for an optical microscope
0.2 µm
Name 2 pros of optical (light) microscopes
- Easy and cheap to operate
- Can have living specimens
Name 2 cons of optical (light) microscopes
- Low resolution & magnification
- Can’t see organelles smaller than 0.2 µm (e.g. ribosomes, endoplasmic reticulum and lysosomes)
- Specimens often need staining to show specific organelles
Why do optical microscopes have a maximum resolution of 0.2 µm?
Due to the long wavelength of light rays
Name 2 Electron Microscopes
- Transmission Electron Microscopes
- Scanning Electron Microscopes
Describe how transmission electron microscopes work
- Use electromagnets to focus a beam of electrons which is then transmitted through the specimen
- Denser parts of specimen absorb more electrons = makes them look darker on image you end up with
State the maximum resolution for a transmission electron microscope
0.1 nm
Name a pro of transmission electron microscopes
- Has highest resolutions & magnification
- See internal structure of organelles e.g. chloroplasts
Name 4 cons of transmission electron microscopes
- Non-living matter only
- Image in black and white and 2D
- Preparation may distort structure/give artefacts
- Vacuum required
- Elaborate preparation - staining is complex
Describe how scanning electron microscopes work
- They scan a beam of electrons across specimen = knocks off electrons from specimens
- Electrons gathered in cathode ray tube to form image
State the maximum magnification of SEMs
x 30,000
State the maximum resolution of SEMs
20 nm
Name 3 pros of SEMs
- Can form complex 3D images of sample
- Can be used on thick specimens
- Magnifications & resolutions are higher than light microscopes
Name 3 cons of SEMs
- Large and expensive & difficult to operate
- Specimens has to be mounted in vacuum
- Specimen has to be dead
What are 2 differences between fungal and plant cells?
In fungal cells:
Cell walls are made from of chitin & they don’t have chloroplasts
What is the function of the cell-surface (plasma) membrane?
Regulates movement of substances into and out of cells
(has receptor molecules on it and therefore responds to chemicals and other proteins )
What is the function of the nucleus?
Holds genetic information of cell
What is the function of the nucleolus?
Makes RNA and ribosomes
What is the function of nuclear pores?
Allow passages of large molecules (e.g. RNA)
What is the nucleoplasm?
Jelly-like material that makes up bulk of nucleus
What is the nuclear envelope?
Double membrane that surrounds nucleus
What is the function of the nuclear envelope?
Controls entry/exit of materials in and out of nucleus & reactions taking place within it
Where is chloroplast found?
Plant cells and some protoctists
Describe the structure of a chloroplast
Two membranes (chloroplast envelope) filled with fluid
- Membranes stacked into layers known as thylakoids
- A whole stack of thylakoid membranes is known as a granum
- Fluid-filled matrix = stroma (starch grains are found there)
Where is chlorophyll found?
In thylakoids & lamellae
Name 3 adaptations of chloroplast
- Granal membranes = large surface area for enzymes, etc (for 1st stage of photosynthesis)
- Fluid of stroma = possess all enzymes (for 2nd stage of photosynthesis)
- Chloroplasts contain DNA and ribosomes = can quickly manufacture some proteins for photosynthesis
What is the function of chloroplast?
Absorbs light for photosynthesis
Describe the structure of a mitochondrion
- Have double membrane filled with fluid
- Inner membrane is highly folded & called cristae
- Inner section is called matrix
What does the matrix in mitochondria contain?
Enzymes involved in respiration
What is the function of a mitochondrion?
Site of aerobic respiration where ATP is produced/energy released
Describe the structure of endoplasmic reticulum
Made up of flattened membrane bound sacs called cisternae
What is the surface of the rough endoplasmic reticulum covered in?
Ribosomes
What is the function of the rough endoplasmic reticulum?
Modifies and transports proteins made on ribosomes
What is the function of the smooth endoplasmic reticulum?
Synthesises and processes lipids
What is the function of the smooth endoplasmic reticulum in the liver cells?
Involved in breaking down toxins
Describe the structure of the Golgi apparatus
- Not a stable structure = constantly changing
- Stacks of membrane-bound flattened sacs
What is the function of a Golgi vesicle?
Stores lipids and proteins made by Golgi apparatus & transport them out of the cell
Describe the function of the Golgi apparatus
- Receives proteins from ER/moves to Golgi
- Modifies proteins
- Proceses/packages them into vesicles
- Vesicle is moved to plasma membrane
- Fuses with it/excoytosis
What is the function of a cell wall?
Supports cell and prevents them from changing shape
(Cell wall is permeable to allow solutions to pass in and out)
What is a lysosome?
Tiny bag of digestive enzymes, surrounded by a single membrane
What is the function of lysosome?
- Can digest invading cells or break down worn out components of cell
- Keeps digestive enzymes away from cytoplasm
Describe the structure of a ribosome
- Has no outer membrane
- Contains 2 sub-units
What is the function of ribosome?
Site of protein synthesis
(mRNA used to assemble proteins from amino acids)
Describe the structure of a cell vacuole
- Membrane-bound organelle found in cytoplasm of plant cells
- Surrounding membrane is called tonoplast
What is the function of a vacuole?
- Maintain pressure inside cell & keep them rigid (stops plants wilting)
- Storage of waste
Name 4 similarities between eukaryotes and prokaryotes
- Plasma membrane
- Cytoplasm
- DNA & RNA
- Ribosomes
Name 4 structural differences between eukaryotes and prokaryotes
Prokaryotes have:
- Smaller ribosomes (70s type)
- No true nucleus (free, floating circular DNA)
- No membrane-bound organelles
- Cell wall made from the glycoprotein murein
Name 3 additional features that prokaryotic cells can have
- Flagella
- Plasmids
- Capsule
*Pili
What is a flagellum?
Hair-like structure that rotates to make prokaryotic cells move
What are plasmids?
Small loops of DNA
(contain genes for things like antibiotic resistance)
What is the function of a capsule?
Protects bacteria from attack by cells of immune system
Viruses are …
Not cells = Acellular
What are viruses essentially?
Just nucleic acids surround by protein = not alive
What do viruses do?
Invade and reproduce inside the cells of other organisms
Name 3 features of viruses
- Contain core of genetic material - either DNA or RNA
- Have protein coat around core called capsid
- Have attachment proteins which stick out from edge of the caspid
Why do the viruses have attachment proteins?
They allow them to cling on to a suitable host cell
What is cell fractionation?
Process which cells are broken up and organelles they contain are separated out
Name the 3 stages in cell fractionation
- Homogenisation - Breaking Up the Cells
- Filtration
- Ultracentrifugation - Separating the Organelles
What happens in stage 1 (homogenisation) of cell fractionation?
- Cells broken up by homogeniser (blender)
- Added to solution
Why do you break up the cells during fractionisation?
To breaks up the plasma membrane and release the organelles
Name the 3 conditions of the solution used during cell fractionation and why they are used.
- Isotonic - prevens organelles being damaged through osmosis.
- Ice-cold - prevents enzyme activity so proteins are not brokens down.
- Buffered- maintains a constant pH so proteins are not denatured
What happens in stage 2 (filtration) of cell fractionation?
Homogenised cell solution is filtered through gauze to separate any large cell debris or tissue debris from organelles
(organelles = much smaller than debris)
What happens in stage 3 (ultracentrifugation) of cell fractionation?
- Cell fragments poured into tube & put into centrifuge - spun at low speed
- Heaviest organelles (nuclei) at bottom of tube = form thick sediment called a pellet
- Rest of organelles stay suspended in fluid above pellet = called supernatant
- Supernatant is poured into another tube & spun in centrifuge at higher speed
- Heaviest organelles (mitochondria) form pellet at bottom
- Supernatant is spun at higher speed
- Process is repeated at higher speeds until organelles are separated out
State the order of the organelles that are seperated in ultracentrifugation (from heaviest to lightest)
Nuclei to ribosomes
Nuclei, chloroplast, mitochondria, lysosomes, endoplasmic reticulum, ribosomes
Describe how to prepare a ‘temporary mount’ of specimen on a slide
- Pipette drop of water onto slide
- Use tweezers to place thin section of your specimen on top of water drop
- Add drop of stain - iodine dissolved in potassium iodide solution
- Lower cover slip using a mounted needle
Preparing a ‘temporary mount’ of specimen on a slide:
Why do you add a stain?
∵ Highlights objects in a cell
Preparing a ‘temporary mount’ of specimen on a slide:
When adding the cover slip, describe what you should do to avoid getting air bubbles
When adding the cover slip:
- Stand slip upright on slide, next to water droplet
- Carefully tilt and lower it so it covers the specimen
Preparing a ‘temporary mount’ of specimen on a slide:
Why do we try avoid getting air bubbles?
∵ they obstructs your view of specimen
Define Exocytosis
Bulk transport of materials out of a cell from a vesicle
Define Endocytosis
Bulk transport of materials into a cell by the formation of vesicle from the cell membrane
Describe the stages of the cell cycle.
- Interphase - When DNA is replicated (also known as S phase)
- Mitosis - The cell divides through the stages of prophase to cytokinesis. (M phase)
- Growth - the cell produces proteins to use in processes, and may also get ready to divide again. (G phase)
What are the stages of mitosis?
(Interphase)
Prophase
Metaphase
Anaphase
Telophase and cytokinesis
Describe what occurs during prophase
Chromosomes condense after they have now been replicated (they become visible). The chromosomes consist of two identical chromosomes (sister chromatids) joined together at the centromere. The two centrioles (where the spindle fibres originate) move to opposite poles of the cell. Spindle fibres form and the nuclear envelope breaks down, releasing the chromosomes.
Describe what occurs during metaphase
Spindle fibres continue to extend from the centrioles. The chromosomes line up along the equator of the cell and are attached to the centrioles from their centromeres by spindle fibres.
Describe what occurs during anaphase
The sister chromatids seperate at the centromere (so they divide in two). Spindle fibres begin to shorten and the separated sister chromatids are pulled to opposite poles by the spindle fibres
Describe what occurs during telophase and cytokinesis.
The chromosomes arrive at opposite poles and begin to decondense. The nuclear envelope begins to reform around each set of chromosomes. The spindle fibres break down. Once the nuclear envelope has been reformed, the cytoplasm splits, and the cell membrane reforms around the two new daughter cells.
Match the image to the mitotic stage.
A - Anaphase
B - Telophase
C - Cytokinesis
D - Interphase
E - Metaphase
F - Prophase
How do prokaryotic cells divide?
By binary fission, which occurs as follows:
1. The circular DNA replicates and both copies attach to the cell membrane
2. The cell membrane then begins to grow between the two DNA molecules and pinches inwards to divide the cytoplasm.
3. A new cell wall forms between the two DNA molecules, dividing the original cell.
How do viruses replicate?
Viruses are not living, therefore they infect a host cell, and use the host’s replication machinery to replicate. (i.e. the viral DNA is combined with the host DNA so when it replicates its DNA, the viral DNA is also replicated).
