Pack 2 - Cell Structure Flashcards
Define resolution.
The minimum distance apart two objects can be in order for them to be distinguishable as two separate objects.
What determines the resolution of a microscope?
The wavelength of radiation being used. (e.g the wavelength of light)
What is the approximate resolution of a light microscope?
0.2μm
Why is the resolving power of an electron microscope higher than a light microscope?
The wave length of electrons is shorter than the wavelength of light.
What is cell fractionation?
The process where cells are broken up and the organelles they contain are released and separated out.
What THREE conditions must a tissue be under before cell fractionation can take place and WHY?
- Cold - To reduce enzyme activity that may break down ORGANELLES.
- Isotonic (same Ψ as tissue) - to prevent bursting or shrinking of ORGANELLES due to osmosis.
- Buffered (same pH as tissue) - to prevent enzymes denaturing or the changing in the structure ORGANELLES.
Describe cell fractionation in 4 steps.
- Homogenisation - cells are broken up by a blender into a homogenate releasing organelles.
- Filtration - whole cells/debris removed
- Ultracentrifugation - homogenate is spun in a CENTRIFUGE at a low therefore the densest organelles fall to the bottom.
- Repeat - the supernatant is poured of and the process is repeated on the supernatant at higher speeds to obtain less dense organelles.
What is the fluid at the top of a centrifuge tube called after centrifugation?
Supernatant
Order the following organelles by increasing speed of centrifugation.
• Mitochondria
• Nuclei
• Lysosomes
- Nuclei
- Mitochondria
- Lysosomes
How are electrons focused in an electron microscopes?
Using electromagnets (because electrons are negatively charged).
What is an important condition needed for all electron microscopes and why?
A near vacuum - because electrons are deflected and absorbed by air molecules.
What kind of image does a transmission electron microscope (TEM) produce?
2D, Black and White
What is the approximate resolution of a transmission electron microscope (TEM)?
0.1nm
Why can the maximum resolving power of a transmission electron microscope (TEM) no always be produced?
- Difficulties preparing the specimen.
* high energy electron beams required would destroy the specimen.
What are 4 main limitations of a TEM?
- The whole system must be in a near vacuum therefore living specimens cannot be observed.
- A complex staining process is required.
- The specimen must be extremely thin to allow electrons to pass through.
- The image may contain artefacts due to the way the specimen is prepared.
What kind of image does a scanning electron microscope (SEM) produce and how?
3D - Black and white
Rather than penetrating the sample, a SEM passes a beam of electrons over the sample in a regular pattern. The electrons are scattered depending on the surface. A computer builds a 3D image based on the scattering of electrons.
What are the advantages of a SEM over a TEM?
- Specimen does not have to be thin.
* 3D image
What is the approximate resolution of a scanning electron microscope (SEM)?
20nm
Name the 5 components of the nucleus and their roles.
- Nuclear envelope - controls the entry and exit of materials; contains reactions taking place in the nucleus.
- Nuclear pores - allows passage of large molecules in and out of the cell e.g. mRNA
- Nucleoplasm
- Chromosomes - consist of protein bound linear DNA
- Nucleolus - manufactures ribosomal RNA and assembles ribosomes.
Describe the structure of the nuclear envelope.
Double membrane; outer membrane is continuous with the ER; often has ribosomes on its surface.
What are 3 functions of the nucleus?
- Controls protein synthesis through the production of mRNA and tRNA
- Retains genetic material of the cell
- Manufactures ribosomal RNA and ribosomes
Name the 3 components of mitrochondria and their roles.
- Double membrane - controls the entry and exit of materials
- Cristae (extensions of the inner membrane) - large surface area for attachment of enzymes and other proteins used in respiration.
- Matrix - remainder of the mitochondria; contains proteins, lipids, ribosomes and DNA; allows mitochondria to control the production of some of their own proteins.
What is the function of mitochondria?
Site of aerobic stages of respiration.
Produces ATP
Give an example of a cell that would have lots of mitochondria.
Any metabolically active cell - e.g. muscle cell, epithelial cell…
Name the 5 main components of a chloroplasts.
- Chloroplast envelope - highly selective double plasma membrane.
- Thylakoids - contain chlorophyll where light absorption takes place.
- Grana - stacks of thylakoids
- Stroma - fluid containing DNA starch and ribosomes
- DNA - for quick protein synthesis
Give 3 ways chloroplasts are adapted to their function.
- Grana have large surface area for attachment of chlorophyll, electro carriers and enzymes that carry out the first stage of photosynthesis.
- Stroma contains all the enzymes needed in the section stage of photosynthesis.
- Stroma contains DNA and ribosomes for quick manufacture of proteins needed for photosynthesis.
What are the sacs called that the endoplasmic reticulum enclose.
Citernae
What are the 2 functions of the rough endoplasmic reticulum?
- Large surface area containing ribosomes forth synthesis of proteins and glycoproteins.
- Pathway for the transport of materials especially proteins
What are the 2 functions of the smooth endoplasmic reticulum?
- Synthesis store and transport lipids.
* Synthesis store and transport carbohydrates.
Give an example of a cell that would have a large endoplasmic reticulum.
Liver/secretory cells as they manufacture and store large quantities of proteins, carbohydrate and lipids.
Give 5 functions of the Golgi Apparatus
- adds carbohydrates to proteins to form glycoproteins
- produces secretory enzymes
- secretes carbohydrates (such as those to be used in cell walls)
- transports, modifies and stores lipids
- forms lysosomes
What are vesicles.
Small rounded hollow structures that transport molecules from the Golgi apparatus (may be to the cell surface).
What are lysosomes?
Vesicles that contain enzymes such as proteases and lipases as well as lysozyme (enzymes that break down bacteria cell walls).
What are the functions of lysosomes?
- to hydrolyse material ingested by phagocytic cells.
- to release enzymes to outside the cell (exocytosis) to destroy material around the cell.
- to digest worn out organelles.
- break down dead cells.
Describe the structure of ribosomes.
A small sub-unit and a large sub-unit both containing ribosomal RNA and protein.
Name the two types of ribosomes and which type of cell they are found in.
70s - prokaryotic
80s - eukaryotic
Describe the structure of a cell wall.
- number of polysaccharides such as cellulose.
* middle lamella marks the boundary between adjacent cell walls and cements them together.
Name 3 functions of the cell wall.
- Prevent bursting through osmotic pressure.
- Mechanical strength as a whole
- to allow water to pass along the cell and move throughout the plant as a whole.
What type of membrane does a vacuole have and what is it called?
Single membrane - tonoplast
Give 3 functions of a vacuole.
- Support herbaceous parts of plants by making cells turgid.
- Contains sugars and amino acids that may act as a temporary food store.
- Pigment colours petals to attract insects.
Where do all cells come from?
Fertilised egg
What are the main differences between prokaryotes and eukaryotes?
- Lacks a nucleus or any membrane bound organelles.
* Genetic material forms one circular molecule of DNA
What is a bacteria’s cell wall made of?
Murien
What are the 2 main functions of bacterial cell wall?
- Physical barrier
* protects against mechanical damage and osmotic lysis
What are the cell walls of fungi made of?
chitin, glycan and glycoproteins
What three features can prokaryotes have that eukaryotes don’t and what are their functions?
- Plasmid - can reproduce themselves independently; give the cell resistance to harmful substances.
- Capsule - protects from other cells; bacteria can stick together for protection
- Flagellum - locomotion
Give 4 differences between the structure of DNA in prokaryotes and eukaryotes.
- Prokaryotes have no nucleus.
- Prokaryotes have one circular molecules of DNA. eukaryotes have linear DNA
- Prokaryotes can have plasmids
- Eukaryotes’ DNA is associated with proteins called histones.
Describe 4 features of viruses and their functions.
- RNA/DNA as genetic material.
- Capsid - a protein that enclose the genetic material.
- Lipid envelope (some viruses)
- Attachment proteins - used to identify and attach to host cell.
Why is a virus not a living organism?
It cannot survey by itself. Therefore they are described as particles NOT CELLS.
