Cell Structure Flashcards
What is a dry mount (slide prep)
thin slices or whole specimens are viewed with just the coverslip placed on top
e.g. plant tissue or hair
What is a wet mount (slide prep)
water is added to the specimen before lowering the coverslip, a mounted needle prevents air bubbles from forming.
e.g. to view aquatic organisms
What is a squash slide (slide prep)
Wet mounts that you push the coverslip down on to squash the sample to ensure a thin enough layer for light to pass through.
e.g. used to create root tip squash sample to view chromosomes in mitosis
What are smear slides (slide prep)
created using another slide to smear the sample across the slide to create a smooth, thin, evenly coated specimen. A coverslip is then placed on top.
E.g. blood cells in a blood sample
What is differential staining
Technique which involved many chemical stains used to stain different parts of a cell in different colours
What stains are used and for what
Crystal violet or methylene blue- stain negatively charged materials
Microsin and congo red- creates a stained background
Describe gram staining
Gram positive- crystal violet is added and then iodine, alcohol is used to wash away unbound stain. The bacteria appear blue/purple as the stain is retained due to the thicker peptidoglycan cell wall later absorbing the dye
Gram negative- crystal violet can not be absorbed due to their peptidoglycan cell wall being thin, safranin is used as a counterstain which turns them red.
Electron Microscopes
High resolution due to short wavelength of electron beam (small organelles can be visualised)
Image is created using an electromagnet to focus the beam of negatively charged electrons
EM must be in a vacuum because electrons are absorbed by air
Only non living specimens can be examined
Black and white image
Transmission Electron Microscopes
Extremely thin specimens are stained and placed into a vacuum
Electron gun produces beam that passes through the specimen
Some parts of the specimen absorb electrons which makes them appear darker
2D image produced
Scanning Electron Microscope
Specimen doesn’t need to be thin
Electrons are beamed onto the surface and scattered depending on the contours
Produces a 3D image.
Laser Scanning Confocal Microscope
Fluorescent microscope
Image obtained using high light intensity to illuminate specimen using fluorescent dye
High resolution and 3D image
Structure of the nucleus
Nuclear envelope- double membrane
Nuclear pores
Nucleoplasm- granular, jelly like material
Chromosomes- protein bound, linear DNA
Nucleolus- smaller sphere inside which is the site of rRNA production and makes ribosomes
Function of the nucleus
Site of DNA replication and transcription (making mRNA)
Contains the genetic code for each cell
Site of ribosome synthesis
Structure of Flagella
Whip/tail like structure
Function of flagella
For mobility and sometimes as a sensory organelle for chemical stimuli
Structure of cilia
Hairlike projections out of cells
Function of cilia
Can be mobile or stationary
Mobile cilia help move substances in a sweeping motion
Stationary cilia are important in sensory organs such as the nose
Structure of centrioles
Made of microtubules
Occur in pairs to form a centrosome
Function of centrioles
Involved in the production of spindle fibres and organisation of chromosomes in cell division
Structure of cytoskeleton
Network of fibres found within the cytoplasm all over a cell
Consists of microfilaments, microtubules and intermediate fibres.
Function of the cytoskeleton
Provides mechanical strength to cells, helps maintain the shape and stability of a cell. Many organelles are bound to the cytoskeleton
Microfilaments are responsible for cell movement
Microtubules are responsible for creating a scaffold like structure
Intermediate fibres provide mechanical strength
Structure of the endoplasmic reticulum
Folded membranes called cisternae
Rough ER has ribosomes on the cisternae
Function of the Endoplasmic reticulum
Smooth- Synthesis and store lipids and carbohydrates
Rough- Protein synthesis
Structure of golgi apparatus (and vescicles)
Folded membranes making cisternae
Secretary vesicles pinch off from the cisternae
Function of the golgi apparatus and vesicles
Add carbohydrates to proteins to form glycoproteins
Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids
Form lysosomes
Label molecules with their locations
Finished products are transported to the cell surface in vesicles where they fuse with the membrane and the contents are released
Structure of Lysosomes
Bags of digestive enzymes (can contain 50 different)
Function of lysosomes
Hydrolyse phagocytic cells
Break down dead cells (autolysis)
Exocytosis (release enzymes to outside of a cell to destroy material)
Digest worn out organelles for the reuse of materials
Structure of mitochondria
Double membrane
Inner membrane called the cristae
Fluid centre called the mitochondrial matrix
Loop of mitochondrial DNA
Function of mitochondria
Site of aerobic respiration
Site of ATP production
DNA to code for enzymes needed in respiration
Structure of ribosomes
Small, made up of two subunits of protein and rRNA
80s- large ribosomes found in eukaryotic cells (25nm)
70s- smaller ribosome found in prokaryotic cells, mitochondria and chloroplasts
Function of ribosomes
Site of protein synthesis
Structure of chloroplasts
Surrounded by a double membrane
Contains thylakoids (folded membranes embedded with pigment)
Fluid filled stroma contains enzymes for photosynthesis
Found in plants
Function of chloroplasts
Site of photosynthesis
Structure of a cell wall
(in plants and fungi cells)
Plants- made of microfibrils of the cellulose polymer
Fungi- made of chitin (a nitrogen containing polysaccharide)
Function of the cell wall
Provide structural strength to the cell
Structure of plasma membrane
Phospholipid bilayer- molecules embedded within and attached in the outside (such as proteins, carbohydrates and cholesterol)
Function of plasma membrane
Controls the entrance and exit of molecules
Describe the production and secretion of proteins
Polypeptide chains are synthesised by ribosomes on the RER
These chains then travel into the cisternae of the RER where they are packaged into vesicles and sent to the golgi apparatus via the cytoskeleton
They are then modified and packaged into vesicles at the golgi apparatus
The secretory vesicles then carry the proteins to the cell surface membrane where it fuses and releases the proteins via exocytosis
Compare prokaryotic and eukaryotic cells
Prokaryotes are much smaller
Prokaryotes have no membrane bound organelles
Prokaryotes have smaller ribosomes
Prokaryotes do not have DNA contained within a nucleus
Prokaryotes have a cell wall made of murein (a glycoprotein)
Prokaryotes may also contain plasmids, a capsule around the cell and flagella
