cell structure Flashcards
what is magnification
the number of times larger an image appears, compared with the size of the object being viewed
what is resolution
how clearly we can determine two points, the higher the resolution the greater the detail
what is wet mounting
specimens are suspended in a liquid such as water or immersion oil
what is dry mounting
solid specimens are viewed whole or cut into very thin slices
why must we place a cover slip on at an angle (when placing it onto a wet mount)
this is to prevent air bubbles forming under the cover slip
what is the maximum magnification and resolution of a scanning electron microscope (SEM)
- 15 to 200,000 times (magnification range)
- 3-10 Nm (resolution range
what is the maximum magnification and resolution of a transition electron microscope (TEM)
- x 2 million (magnification range)
- 0.5nm (resolution range)
what are the disadvantages of electron microscopes
- the specimen has to be chemically fixed, by being dehydrated and stained
- vacuum required
- large and needs to be installed
- expensive to buy/operate
- specimens must be dead
what is the function of the mitochondrion
mean length = 0.5 to 1 um
- to produce energy in respiration
what is the function of chloroplasts
mean length = 3-10 um
uses light energy in photosynthesis
- convert light energy in to stable chemical energy
what is the function of the Golgi apparatus
mean length = 0.5 to 2.0 um
to function as a factory in which proteins are processed and transported to the plasma membrane etc.
what is the function of the smooth ER
mean length =30nm to 50nm
it synthesis and stores lipids including cholesterol and phospholipids to produce new cellular membranes
what is the function of the rough ER
mean length = 20nm to 30nm
to produce proteins that will become part of the Endomembrane system, the plasma or will be secreted
(the endomembrane systems is all of the membranes within the cell)
what are centrioles
- centrioles, move to the poles (opposite ends of the cell) of the cell
- froms spindle fibres, which often attach to chromosomes
what are flagella
- flagella are prokaryotes/ bacteria
- ## whip like movement
what are cilia
- same structure as the flagella, but shorter
- beating movement
- arranged in clusters
what are microfilaments
- filaments found in the cytoplasm
- help the cell move
- change shape (endocytosis and exocytosis)
what are microtubles
- little tubes (microscopic)
- form the spindle
- make up cilia and undulipodia, so help, with the movement of substances
- motor proteins, allow them to move via ATP
what are intermediate fibres
- extended between cells and help to stabilise the tissue
what are lysosomes
- Specialist forms of vesicles which contain hydrolytic enzymes (enzymes that break biological molecules down)
- Break down waste materials such as worn-out organelles, used extensively by cells of the immune system and in apoptosis (programmed cell death)
State some advantages and disadvantages of light microscopes
easy to use, portable, can be used to observe living specimens (tissues) DISADS: Limited magnification and resolution so fine detail cannot be observed
State the maximum magnification and resolution for a light microscope
M = 1500 - 2000 times; R = 200nm (0.2µm)
Describe reasons why we use staining in microscopy
Coloured chemicals that bind to molecules on the specimen, increasing contrast and making the specimen easier to see; some stains bind to specific cell structures in differential staining, e.g. acetic orcein binds to DNA and stains chromosomes dark red
Describe differences in how the image is formed between TEMs, SEMs and LSCMs
- TEM: electrons pass straight through specimen (2D black and white image);
- SEM: electrons bounce off specimen surface and focused (3D black and white image);
- LSCM: laser scans specimen point by point and stacks layers of the image at different depths (3D image)
Describe 4 disadvantages of electron microscopy
- Specimen has to be dead (as observed in a vacuum)
- requires specialist training to use; heavy metallic salt stains hazardous to human health;
- complex preparation process means artefacts may be produced (distorts image);
- high energy electron beam can damage the specimen (distorts image)
State 5 success criteria that must be considered when making a biological drawing of a specimen
Use a sharp pencil, ensure drawing has a title and a scale bar, make appropriate annotations detailing structure and function, use a ruler to draw label lines which do not overlap (with no arrowheads), ensure all lines in image are clear and continuous (unbroken), NO shading
State the formula for calculating magnification
magnification = image size/actual size
Describe the structures and functions of the various components of the nucleus
- Nuclear envelope: separates contents of the nucleus from the rest of the cell, contains nuclear pores which allow movement of messenger RNA (mRNA) OUT of the nucleus
- nucleolus: contains ribosomal RNA to synthesise ribosomes; nucleoplasm: contains chromatin which is where DNA is stored
Describe the structure and function of the rough endoplasmic reticulum (rER)
A system of membranes containing fluid filled cisternae, continuous with nuclear membrane and covered in ribosomes. It acts as both an intracellular transport system and a site of protein synthesis (translation on ribosomes)
Describe the structure and function of the smooth endoplasmic reticulum (sER)
Similar to rER but more tubular structure with NO ribosomes. Site of cholesterol, steroid hormone, lipid synthesis
Describe the structure and function of the Golgi apparatus
A stack of membrane-flattened sacs; secretory vesicles bring materials to and from the Golgi. It is the site of protein modification (e.g. adding sugar groups to make glycoproteins), protein folding (e.g. into an enzyme/hormone). Modified proteins can then either be stored in the cell or exported via exocytosis at the plasma membrane
Describe the structure and function of a mitochondrion
Double membrane with inner membrane folded into cristae (provides a large surface area for electron carrier proteins in aerobic respiration and significant ATP production); contains a fluid filled matrix containing enzymes (for respiration) and mitochondrial DNA (for self-replication and protein synthesis)
Describe the structure and function of chloroplasts
Double membrane, inner membrane continuous with stacks of flattened membrane sacs called thylakoids (stacks of thylakoids are called grana) which contain chlorophyll; fluid-filled stroma (contains enzymes for photosynthesis); contains loops of DNA (for protein synthesis) and starch grains (carbohydrate storage)
Describe the structure and function of the components of the vacuole
Contains cell sap (water and solutes which maintain cell stability by exerting pressure on the cell wall…turgid); surrounded by a tonoplast (vacuolar membrane)
Describe the structure and function of lysosomes
Single-membrane bound vesicles containing hydrolytic enzymes; lysosomes are abundant in phagocytes (neutrophils and macrophages). Lysosomes can engulf dead/damaged organelles and foreign matter and recycle the digested components
Describe the structure and function of centrioles
“9 + 3” arrangement of microtubules (made of tubulin); pairs of centrioles are arranged at right angles to each other. Responsible for spindle fibre formation during cell division
Describe the structures and function of cilia and flagella
“9 + 2” arrangement of microtubules; cilia can be stationary (sensory role) or mobile (beat rhythmically to move mucus from airways); flagella used for cell motility
Outline briefly the structures and functions of three components of the cytoskeleton
Microfilaments (composed of actin protein fibres; responsible for cell movement and contraction during cytokinesis); microtubules (composed of globular tubulin proteins; scaffold shale of cell and important in organelle movement working with motor proteins dynein and kinesin); intermediate fibres (many proteins; mechanical strength, anchor nucleus in cytoplasm)
Describe how a protein is synthesised and modified before leaving the cell
Synthesised on ribosome (on rER or free floating), travel through rER in cisternae and pinched off into a vesicle; vesicle moves via microtubules towards Golgi; vesicle fuses with face of Golgi and is modified; modified protein leaves Golgi in vesicle and travels to plasma membrane; vesicle fuses with plasma membrane and exits the cell via exocytosis
Describe the main differences between eukaryotes and prokaryotes
Prokaryotes are much smaller, they have no membrane-bound organelles, less well-developed cytoskeleton and no centrioles; cell wall made of murein (not chitin or cellulose); free-floating loop of DNA (and plasmids)
Describe the similarities between chloroplasts/mitochondria and prokaryotes
- Contain 70s ribosomes
- Contain loops of DNA
- contain RNA
- divide by binary fission
