2.1 - E - Cell Structure Flashcards
What is a cell?
The smallest structural and functional unit of an organism
Define Organelle
Sub-cellular structures which have a specialised function
Define magnification
The degree to which the size of an image is larger than the object itself
What is a photomicrograph?
A photograph of an image seen using an optical microscope
Define resolution
The degree to which it is possible to distinguish between 2 objects that are very close together. The higher the resolution, the greater the detail.
What is the equation to work out magnification?
Magnification = Image size / Actual size
I.A.M
List 4 good things about light (optical) microscopes
Relatively cheap
Easy to use
Portable and can be used anywhere
Able to be used to study whole living specimens
What is the equation for working out total magnification?
Total magnification = Objective lens magnification x eyepiece lens magnification
What are the 4 types of microscope?
Light (Optical)
Transmission Electron Microscope (T.E.M)
Scanning Electron Microscope (S.E.M)
Laser Scanning Microscope
Define Staining
Coloured chemicals that bind to substances which allow them to be seen
What stain makes DNA visible and what colour is it?
Acetic orcein stains DNA dark red
Define Sectioning
Specimens embedded in wax and then thin sectors are cut
What is the order of units of measurement?
m cm mm um nm pm
Define Division Of Labour
Each organelle having a specific role in keeping the cell alive
Define Ultrastructure
The detail inside cells
How do electron microscopes work?
Generate a beam of electrons
Electromagnetic snare used to focus the electrons onto a specimen (instead of lenses)
The image produced from the electron beam transmitted to a screen and creates a black and white image
What is important about the specimen used by electron microscopes?
They must be dead - they have to be in a vacuum
What is the highest magnification and resolution of a light microscope?
x 1,500
200nm - size of a light wave
What is an eyepiece graticule?
A measuring device. It is placed in the eyepiece of a microscope and acts as a ruler when you view an object under the microscope.
What is a stage graticule?
A precise measuring device. It is a small scale that is placed on a microscope stage and used to calibrate the value of eyepiece divisions at different magnifications
What is the maximum magnification and resolution of a T.E.M?
x 500,000
0.1nm / 100pm
(Highest of any microscope)
How do T.E.Ms work?
They produce black and white 2D images
The denser parts absorb more electrons and makes them look darker on the image
What is the maximum magnification and resolution of a S.E.M?
x 100,000
10nm
How do S.E.Ms work?
The electrons bounce off the surfaces to give a 3D image
What is the other name for the Laser Scanning Microscope?
Confocal Microscope
Explain how Laser Scanning Microscopes work
They use laser light to scan an object point by point and assemble pixel information on a computer screen
What is the cytoskeleton?
The network of protein fibres within the cytoplasm that gives structure and shape to the cell
What are the 4 parts of the cytoskeleton?
Microtubules
Flagella
Cilia
Filaments (Intermediate and Actin)
Explain Microtubules
Main part of the cytoskeleton
Hollow cylinders of tubular (protein) (25nm in diameter)
They maintain the cell’s shape and connect organelles to each other to keep them in place
Their motors use ATP to move organelles along the fibres (chromatids in mitosis and vesicles from RER to the Golgi apparatus)
Explain Flagellum
Tail like structures thar move cells
1 or 2 per cell
Move by motor proteins on the microtubules pushing against each other, causing it to bend, creating movement
Explain Cilia
Less than 10um Waft substances Large numbers on ciliated epithelial cells Rare in plants Eg: mucus and eggs in ovaries
Explain Intermediate and Actin Filaments
Intermediate:
Thick cables made of keratin with a 10nm diameter
Maintain cell’s shape and anchor the nucleus and organelles
Actin:
2 intertwined strains of actin with a 7nm diameter
Maintain cell’s shape and cause muscle contractions
Involved in cytokinesis
What are vesicles?
Membrane bound sacs, used to carry substances around
Explain the Nucleus’ structure and function
Contains DNA - the control centre of the cell
Surrounded by a double membrane with pores
It transmits genetic information and provided instructions for protein synthesis
Explain the Nucleolus’ structure and function
Does not have a membrane around it; contains RNA
Where ribosomes are made
Explain the Nuclear Envelope’s structure and function
The double membrane that surrounds the nucleus that has pores.
Separates the contents of the nucleus from the rest of the cell. In dissolved substances can pass through.
Larger substances can leave the nucleus.
Explain the Rough Endoplasmic Reticulum’s structure and function
System of membranes that contain fluid-filled cavities (Cisternae).
It is covered in ribosomes.
It’s an intercellular transport system. The cisternae create channels that move substances from one part of a cell to another.
Large S.A for ribosomes, which form amino acids to make proteins and are then moved to the Golgi apparatus
Explain the Smooth Endoplasmic Reticulum’s structure and function
System of membranes, but no ribosomes.
Contains enzymes that catalyse reactions involved with lipid metabolism.
Explain the Golgi Apparatus’ structure and function
Consists of a stack of membrane-bound flattened sacs. Secretory vesicles bring substances/materials to and from it.
Modifies and packages proteins - adds lipids.
Folded into 3D shapes.
Put into vesicles.
Explain the Mitochondria’s structure and function
2-5 um long.
Surrounded by 2 membranes with a fluid-filled space between them. Inner part of mitochondrion is a “fluid-filled matrix”
It is the site of production of ATP during aerobic respiration.
They are self-replicating; abundant in metabolic areas (liver/synapses)
Explain the Ribosomes’ structure and function
Spherical, approx 20nm diameter.
Made of ribosomal DNA and made in the nucleolus as 2 separate organelles which exit then fuse. Most attach to RER - some roam free in the cytoplasm.
They synthesise proteins on the RER or are assembly points for proteins that will be used inside the cell.
Explain the Lysosome’s structure and function
Small bags formed from the Golgi apparatus.
Surrounded by a membrane and contain powerful hydrolytic (digestive) enzymes.
They keep the hydrolytic enzymes separate from the rest of the cell.
They engulf and digest old organelles and return the components to the cell to be reused.
Explain the Centriole’s structure and function
Consist of 2 bundles of microtubules at right angles to each other.
Spindle forms from centrioles during mitosis.
Also involved in the formation of cilia and undulipodia (flagella).
They multiply underneath the surface membrane the sprout outwards.
Not commonly found in plants (some unicellular algae)
Explain the Chloroplast’s structure and function
4-10um and only found in plants and some protists.
Contain loops of DNA and starch grains.
Surrounded by a double membrane/envelope.
Inner membrane contains stacks of flattened membrane sacks: Thylakoids, which contain chlorophyll. Each stack of thylakoids is a Grana.
The fluid-filled matrix is called the stroma.
They are the site of photosynthesis and split hydrogen bonds in water.
They are abundant in leaf cells.
Explain Vacuoles
Found in plant cells only The membrane (tonoplast) is filled with waters and sugars to push against the cell wall to keep the cell turgid
What are plant cell walls made out of?
Cellulose
What do the cell walls of plant cells do?
Provide strength and support
Maintain the cell’s shape
Contribute to the strength and support of the whole plant
Are permeable and allow solutions to the pass through
Explain the process in making and secreting a protein
Instructions are transcribed in the nucleus into messenger RNA (mRNA)- transcription.
It leaves through the nuclear envelope and is magnetised to the RER.
Here, it is translated and protein molecules are assembled.
The molecules are pinched off in vesicles and travel to the Golgi apparatus where they fuse.
The Golgi apparatus processes and packages the molecules ready for release.
Vesicles fuse with the cell surface membrane.
Cell surface membrane opens to release the molecules.
What similarities do eukaryotic and prokaryotic cell’s have?
A plasma membrane
Cytoplasm
Ribosomes
DNA & RNA
What’s different about a prokaryotic cell compared to a eukaryotic cell?
Prokaryotes are much smaller
They don’t have a nucleus
They have a much less well-developed cytoskeleton with no centrioles
They have a cell wall made of peptidoglycan and not cellulose
Plasmid and chromosomal DNA
Smaller ribosomes
What are pili and what are their purpose?
Small, hair-like structures that allow bacteria to attach to cells
What are prokaryotic cell walls made out of?
Peptidoglycan
