cell structure Flashcards
Define Magnification
How many times bigger the image is than the specimen (object)
Define Resolution
Minimum distance apart that two objects can be in order for them to appear as separate items
what is the equation for magnification?
m = I/A
what is cell fractionation?
the process where cells are broken up and the different organelles they contain are separated out
why is the tissue placed in a cold, buffered, isotonic solution?
cold- reduce enzyme action that might break down organelles
buffered- so that pH does not denature proteins
isotonic-to prevent bursting or shrinking via osmosis
what is homogenation?
cells are broken up by homogeniser which releases organelles from the cell. The homogenate is then filtered to remove large debris
what is ultracentrifugation?
- where organelles are separated by a centrifuge.
- Filtrate is spun at low speed at first to allow heaviest organelles to form sediment.
- liquid at top is removed to leave just sediment.
- liquid is spun at higher speed and process is repeated so that each time, the next heaviest organelle is separated out
State the maximum magnification for an optical microscope
x 1500
State the maximum resolution for an optical microscope
0.2 µm
Name 3 pros of optical microscopes
Easy and cheap to operate
Can have living specimens
can see in colour
Name 2 cons of optical microscopes
Low resolution & magnification so can’t see organelles smaller than 0.2 µm (e.g. ribosomes, endoplasmic reticulum and lysosomes)
Specimens often need staining to show specific organelles
Why does optical microscopes have a maximum resolution of 0.2 µm?
because of the long wavelength of light rays
what is a TEM?
Transmission electron microscope
consists of an electron beam focused on to specimen. Some parts absorb so appear darker. This creates a 2d image
State the maximum resolution for a transmission electron microscope
0.1 nm
State the maximum magnification for a transmission electron microscope
x 10 000 000
Name a pro of transmission electron microscopes
Has highest resolutions & magnification
so can see internal structure of organelles e.g. chloroplasts
Name 4 cons of transmission electron microscopes
can not observe living organisms as system must be in a vacuum
complex staining process
not in colour
may contain artefacts which are things that appear in the image as a result of the preparation process.
what is a SEM?
Scanning electron microscope that directs a beam of electrons on to surface of specimen, forming a 3D image.
what 2 instruments are used to measure the size of objects?
eyepiece graticule and stage micrometer
what is the structure and function of the nucleus?(5)
nucleus contains cell’s hereditary material in the chromosomes
nuclear envelope is a double membrane that surrounds nucleus controlling entry and exit of materials
nuclear pores allow passage of large molecules e.g. mRNA out of the nucleus
nucleoplasm is jelly like substance that makes up bulk of nucleus
nucleolus manufactures ribosomal RNA and ribosomes.
What are chromosomes made of?
DNA bound to histone proteins
what is the structure and function of the mitochondria?(4)
Have double membrane, the inner membrane is highly folded & called cristae
cristae provide large surface area for attachment of enzymes involved in respiration
Inner section is called matrix containing protein lipids ribosomes and DNA that allow for production of proteins
mitochondria are the site of aerobic respiration so are plentiful in cells that need ATP
what is the structure and function of chloroplasts?(4)
contain double membrane that is highly selective
grana are stacks of thylakoids that contain chlorophyll for LDR of photosynthesis. membrane provides large surface area for attachment.
stroma is fluid filled matrix where LIR of photosynthesis occurs
contains DNA and ribosomes so can easily produce proteins.
what is the structure and function of the rough endoplasmic reticulum?(3)
network of flattened membrane bound sacs called cisternae
covered in ribosomes
provides large surface area for synthesis of proteins and glycoproteins and transports these.
what is the structure and function of the smooth endoplasmic reticulum?(2)
no ribosomes, continuous with RER
synthesises, stores and transports lipids and carbohydrates
what is the structure and function of the Golgi apparatus?(3)
Stacks of membrane-bound flattened sacs called cisternae
transports, modifies and stores lipids and proteins
form lysosomes by pinching off cisternae
What is a lysosome and what is its function?(4)
vesicles containing enzymes e.g. lysozymes
hydrolyse material ingested by phagocytic cells
release enzymes outside cell so material outside cell can be destroyed
digest worn out organelles so that useful chemicals can be reused
what is the structure and function of ribosomes?(2)
two subunits each containing ribosomal RNA and protein.
sight of protein synthesis
what are the 2 types of ribosomes and where are they found?
80S- in eukaryotic
70S- in prokaryotic
what is the function of a cell wall?
provide mechanical strength to prevent cell bursting under osmotic pressure
what is the difference between plant and fungal cell walls?
plant- made of cellulose
fungi- made of chitin
what is the structure and function of the vacuole?(3)
fluid filled sac bound by membrane called tonoplast
support herbaceous plants by making cells turgid
contains sugars, amino acids that may be used as temporary food store
name and explain 5 structures of prokaryotic cells
cell wall-protects against mechanical damage
capsule-protects and helps groups of bacteria stick together
cell-surface membrane-controls entry and exit
circular DNA-holds genetic information
plasmid-contains survival genes
Name 4 structural differences between eukaryotes and prokaryotes
prokaryotes:
Smaller ribosomes (70s type)
No true nucleus (free, floating circular DNA)
DNA not associated with proteins
No membrane-bound organelles
Cell wall made from the glycoprotein murein
what are viruses?
acellular (no organelles)
non living particles(They cannot reproduce independently)
Name 5 features of viruses
Contain core of genetic material - either DNA or RNA
Have protein coat around core called capsid
Have attachment proteins which stick out from edge of the caspid
lipid envelope
may have flagella
What happens in interphase?
G1- growth of cell
S1-synthesis of organelles
G2-further growth
the two copies of DNA are joined by a centromere
What happens in prophase?
chromosomes condense and become visible
nucleolus disappears and nuclear envelope breaks down
What happens in metaphase?
chromatids joined by a centromere line up along the equator of the cell
What happens in anaphase?
spindle fibres from centrioles attach to centromeres
centromeres divide and each chromatid is pulled to opposite poles of the cell
What happens in telophase?
chromosomes elongate and become thinner, leaving chromatin
nucleolus and nuclear envelope reform
what is cytokinesis?
when the cytoplasm and membrane divide
what is cancer?
abnormal and uncontrolled cell division
