Cells & Microscopy Flashcards
the nucleus (3)
- normally spherical
- the largest organelle in eukaryotic cells (10-20nm)
- contains DNA arranged in chromosomes
list the four parts of a nucleus
the nuclear envelope
nuclear pores
chromatin
the nucleolus
the nuclear envelope (2)
- a double membrane that surrounds the nucleus
- controls the entry and exit of substances in and out of the nucleus
nuclear pores
allow the passage of large molecules, such as mRNA, out of the nucleus
chromatin (2)
- linear DNA which is histone bound
- condenses into visible chromosomes during nuclear division
the nucleolus (2)
- small, spherical region of the nucleus within the nucleoplasm
- manufactures rRNA and makes ribosomes
the nucleus: FUNCTIONS (4)
- stores genetic information; codes for the primary structure of polypeptides
- production of mRNA via transcription
- production of rRNA that makes up ribosomes
- location where semi conservative replication occurs
the mitochondrion
where ATP is synthesised by aerobic respiration
list the four parts of a mitochondrion
double membrane
cristae
intermembrane space
the matrix
double membrane in a mitochondrion
controls the entry and exit of molecules in and out of the mitochondria
cristae (2)
- extensions that form from folds of the inner membrane
- provide a large surface area
the intermembrane space
the space between the inner and outer membrane
the matrix (2)
- contains proteins, lipids, mitochondrial DNA and 70s ribosomes
- allow the mitochondrion to make its own proteins for respiration, independently of the nucleus
state the two types of endoplasmic reticulum
rough endoplasmic reticulum (RER)
smooth endoplasmic reticulum (SER)
rough endoplasmic reticulum (RER) (3)
- the outer surface is coated in 80s ribosomes
- large surface area for protein synthesis
- packages proteins into vesicles to transport them to the golgi
smooth endoplasmic reticulum (4)
- the outer surface is not coated in ribosomes
- synthesise, store and transport lipids
- synthesise, store and transport carbohydrates
- packages them into vesicles to transport them to the golgi
golgi apparatus (4)
- sorts and modifies proteins
- by adding carbohydrates or lipids onto them to form a “glycoprotein” or “glycolipid”
- these modified proteins are packaged into vesicles again
- these vesicles then fuse with the cell surface membrane, releasing their contents outside the cell via exocytosis
lysosomes (3)
- contain and release hydrolytic enzymes
- also contain lysozymes (enzymes that hydrolyse the walls of certain bacteria)
- they isolate hydrolytic enzymes from the rest of the cell before releasing them
lysosomes: FUNCTIONS (4)
- fuse with foreign materials ingested by phagocytic cells and then release its hydrolytic enzymes
- release enzymes to the outside of the cell in order to hydrolyse molecules there
- break down damaged and worn out organelles (the useful molecules they are made from can be reused)
- completely break down cells after they have been used (autolysis)
what are ribosomes made up of?
ribosomal RNA
what is the role of ribosomes?
to synthesise proteins
where can ribosomes be found? (2)
- cytoplasm
- RER
list the two main types of ribosomes
- 80s (larger; found in eukaryotic cells)
- 70s (smaller; found in prokaryotic cells)
chloroplasts
the organelles that carry out photosynthesis
list the four parts of a chloroplast
double membrane
grana
thylakoids
stroma
grana
stacks of up to 100 disc like structures
thylakoids (3)
- disc like structures
- made from membranes
- within the membranes is the photosynthetic pigment called chlorophyll
stroma
a fluid filled matrix where the second stage of photosynthesis occurs
cellulose cell wall (2)
- consists of microfibrils; provides strength and rigidity to the cell wall
- prevents the cell from bursting under the pressure created by the entry of water by osmosis
what is a fungi cell wall made of?
chitin
state the three purposes of plant vacuoles (3)
- provide support, making cells turgid
- sugars and amino acids stored, could act as a temporary food source
- the pigments may colour petals and attract pollinating insects
define what a tissue is
a group of cells working together to perform a specific function
define what an organ is
a group of tissues working together to perform a specific function
what are the differences between a prokaryotic cell and a eukaryotic cell? (6)
PROKARYOTIC
- DNA is circular; not associated with histones
- contains no membrane bound organelles
- has no ‘true’ nucleus; DNA is free in the cytoplasm
- contains smaller ribosomes (70s)
- some have capsule, one or more flagella, one or more plasmids
- cell wall made of murein
EUKARYOTIC
- DNA is linear; associated with histones
- contains membrane bound organelles
- has a nucleus; DNA contained within nuclear membrane
- contains larger ribosomes (80s)
- do not have a capsule, flagella or plasmids
- plant cells have a cell wall made of cellulose
viruses are ___________
acellular
viruses: FEATURES (7)
- non living
- require a living cell to replicate inside
- contain DNA or RNA, which can be single or double stranded
- genome is surrounded by a protein called a capsid
- envelope contains attachment proteins
- no organelles
- has enzymes that it uses to replicate its genetic information
how are retroviruses different to viruses?
they contain an enzyme called reverse transcriptase, which allows them to produce a copy of DNA from viral RNA
what do the attachment proteins on the envelope of a virus do?
enable the virus to bind to host cells
define resolution
the ability to distinguish between objects that are close together
light (optical) microscopes (3)
- focussed using glass lenses
- viewed using the eye or photographic film
- cellular structures often need to be stained with a coloured dye to make them visible
which microscope can view both living and dead specimens?
light
what is a limitation of the light microscope?
the magnification is limited to x1500, meaning none of the smaller organelles can be observed
why is the magnification of a light microscope limited?
by using more lenses, a LM can magnify by a larger amount, but at these higher magnifications the microscope loses resolution
the ___________ the wavelength of light/electrons, the better the resolution
shorter
how many types of electron microscopes are there?
TWO
- transmission electron microscope (TEM)
- scanning electron microscope (SEM)
why does a beam of electrons have better resolution than light?
because it has a very short wavelength
how does a transmission electron microscope work? (3)
- specimens are fixed in resin and sliced thin, so they must be dead
- the electrons are fired through the specimen
- thin parts appear light, thicker areas appear darker
how are the specimens prepped for a TEM? (2)(+ 1)
- put in a vacuum
- stained using heavy metals
- a complex process that can create artefacts (which shouldn’t be there)
how does a scanning electron microscope work? (2)
- specimens are not sliced
- electrons bounce off the surface of the specimen
what is the only way you can tell if the image is made in an SEM?
the image produced will be 3D
CELL FRACTIONATION AND ULTRACENTRIFUGATION: step 1 (3)
- tissue is homogenised in a blender
- in an ice cold, isotonic, buffered solution
- to break open the cells and release organelles
why does the solution need to be…
ice cold
isotonic
buffered
ice cold
reduces the action of enzymes that would damage organelles
isotonic
same water potential to prevent osmosis so that cells don’t burst (lysis) or shrivel
buffered
maintains pH
CELL FRACTIONATION AND ULTRACENTRIFUGATION: step 2 (2)
- mixture is filtered to remove any large pieces of debris
- produces a solution of suspended organelles (supernatant)
CELL FRACTIONATION AND ULTRACENTRIFUGATION: step 3 (4)
- differential centrifugation
- centrifuged at a low speed
- densest organelles are forced to the bottom of the tube into a pellet
- pellet is removed
CELL FRACTIONATION AND ULTRACENTRIFUGATION: step 4 (4)
- supernatant is now centrifuged at a higher speed
- smaller, less dense organelles are forced to the bottom of the tube into a pellet
- pellet is removed
- supernatant can be centrifuged at a higher speed
