Topic 3 - Cells Flashcards
Define the term eukaryotic cell.
DNA is contained in a nucleus, contains membrane-bound organelles.
Define the term prokaryotic cell.
DNA is ‘free’ in cytoplasm, no organelles
Describe the structure and function of the cell-surface membrane.
Structure: ‘Fluid mosaic’ phospholipid bilayer with extrinsic and intrinsic proteins embedded.
Functions: Isolate cytoplasm from extracellular environment.
Selectively permeable to regulate transport of substances.
Cell signalling and recognition
Describe the structure of the nucleus.
Surrounded by nuclear envelope, a semi-permeable double membrane.
Nuclear pores allow substances to enter/exit.
Dense nucleolus made of RNA and proteins.
Describe the function of the nucleus.
Contains DNA.
Controls cellular processes.
Describe the structure of a mitochondrion.
Surrounded by double membrane folded inner membrane forms cristae.
Fluid matrix containing mitochondrial DNA, respiratory enzymes, lipids, proteins.
Describe the structure of a chloroplast.
Vesicular plastid with double membrane.
Thylakoids: flattened discs stack to form grana. These contain photosystems with chlorophyll.
Intergranal lamellae: tubes attach thylakoids in adjacent grana.
Stroma: fluid-filled matrix.
State the function of mitochondria.
Site of aerobic respiration to produce ATP.
State the function of the chloroplasts.
Site of photosynthesis to convert solar energy to chemical energy.
Describe the structure and function of the Golgi apparatus.
Structure: Planar stack of membrane-bound, flattened sacs.
Functions: Modifies and packages proteins for export.
Synthesis glycoproteins.
Processes enzymes.
Transport, modify and store lipids.
Describe the structure and function of the lysosomes.
Structure: Sac surrounded by single membrane. It is a vesicle produced by the golgi apparatus.
Contains digestive hydrolytic enzymes called lysozymes.
Functions: Digests contents of phagosome.
Exocytosis of digestive enzymes.
What is magnification?
How much bigger the image you see is than the actusl specimen itself.
What is resolution (resolving power)?
The ability to distinguish between two points that are close together as separate structures.
What is the equation that links magnification, image size and real size?
Magnification = Image size / real size.
What is the purpose of cell fractionation and ultracentrufication?
To break open cells and separate out organelles.
Why must the tissue be place in a cold, buffered and isotonic solution?
Cold - Reduces enzyme activity that might break down the organelles.
Buffered - so that the pH does not change and effect the structures of organelles.
Isotonic - to prevent organelles bursting or shrinking as a result of loss or gain of water.
Describe the process of ultracentrifugation.
1.) Break open cells/tissues and filter.
2.) Add this to cold, buffered and isotonic solution.
3.) Centrifuge at a low speed until heaviest organelles settle out. Remove the pellet.
4.) Centrifuge again at a higher speed.
What are the two types of electron microscopes?
Transmission Electron Microscope
Scanning Electron Microscope
How does a TEM work?
Uses beams of electrons, which have a much shorter wavelength than light.
What can TEM’s do?
Can magnify objects up to 500,000 times the size.
Have a very high reolution.
What are some limitations of the TEM?
Living specimens can not be viewed as the whole system must be in a vacuum.
The specimen has to be extremely thin.
Specimens are killed and chemically ‘fixed’. This takes time and is very complex.
This method can result in artefacts.
Can only form 2D images.
Image is in black and white
How does a SEM work and what are its advantages?
Electrons are passed across the surface of the specimen.
Scattered electrons form an image on the screen.
Specimens do not need to be thin.
Less complex and time consuming to prepare than TEM.
Less chance of artefacts.
What are the limitations of a SEM?
Can only form 3D images.
Lower resolving power than TEM.
What is the structure of the smooth endoplasmic reticulum?
Membranes enclose a network of flattened tubes called cisternae.
Has no ribosomes attached so referred to as smooth.
What is the function of the smooth endoplasmic reticulum?
Site of lipid and carbohydrate synthesis, store and transport.
What is the structure of the rough endoplasmic reticulum?
Membrane enclose a network of flattened tubes called cisternae.
It is continuous with the outer nuclear envelope.
Has ribosomes attached .
What are the functions of the Rough Endoplasmic reticulum?
Protein synthesis happens here.
Provides a pathway for the transport of materials.
What is the cell wall in plants and algae mad of?
Cellulose and glycoproteins.
What are the cell walls in fungi made of?
Chitin, glycans and glycoproteins.
What are the functions of the cell wall?
Provides mechanical strength when under osmotic pressure and gives strength to the plant as a whole.
Allows water to pass along it, so contributes to water movement through the plant.
Describe the structure and function of the plant vacuole.
Structure: Fluid-filled sac containing a solution of mineral ions, sugars, amino acids, waste and pigments.
Function: Gives cells turgidity - overall support
Sugars and amino acids can act as a temporary food store.
Pigments give colour - e.g. petals to attract pollinators.
What features are special about a prokaryotic cell?
Much smaller than eukaryotic cells.
No nucleus
No membrane bound organelles.
What is the function of the slime capsule in a prokaryote?
Prevents the cell from drying out - slippery
What is the function of the cell wall in a prokaryote?
Prevents the cell from bursting in too much water
How is the DNA arranged in a prokaryote?
Single circular DNA molecule that floats free in the cytoplasm.
What is the structure and function of the Flagellum?
Hair-like structure that rotates to propel the cell
What is the function of plasmids?
Can code for properties such as antibiotic resistance.
What is the function of ribosomes in a prokaryote?
Site of polypeptide synthesis
What does mitosis produce?
Two new identical daughter cells that have the same number of chromosomes as the parent cell.
Why is division by mitosis important?
Growth
Differentiation/reproduction
Repair
What are the stages of mitosis in order?
Interphase
Prophase
Metaphase
Anaphase
Telophase
What happens during prophase?
Chromosomes condense and first become visible.
The nuclear envelope breaks down.
What happens during metaphase?
Spindle fibres connect to centromeres on chromosomes.
The spindle fibres pull the chromosomes so they line up the equator.
What happens during anaphase?
The spindle fibres pull the sister chromatids away from each other to opposite poles of the cells.
What happens during telophase?
The individual sister chromatids uncoil.
The nuclear envelope reforms around each set of sister chromatids at the two poles.
Cytokinesis occurs and the cytoplasm and cell membrane split to form 2 individual daughter cells.
What is the equation for mitotic index?
(Number of cells with condensed chromosomes / total number of cells) x100
What are the four stages of the cell cycle?
G1
S
G2
Mitosis
What happens during the G1 phase of the cell cycle?
Period of cell growth before the DNA is duplicated.
What happens during the S period of the cell cycle?
DNA is replicated.
What happens during the G2 phase of mitosis?
Period after DNA is replicated - the cell prepares for division.
What are the three stages of interphase?
G1
S
G2
Why is it wrong to describe interphase as the resting phase?
There may be no division but there is a period of intense chemical activity.
When does the mass of DNA rise and fall?
Mass of DNA rises during DNA replication in the S phase and then falls during cytokinesis.
What causes cancer?
Uncontrolled cell division
`What is the difference between a malignant and benign tumor?
Benign - grow slowly, more compact and less likely to become life threatening.
Malignant - Grow quicker, less compact, more life threatening.
How do cancer cells move to different parts of the body?
The blood
