cells, structure, microscopy Flashcards
draw the structure and state the function of the nucleus?
site of DNA replication and transcription (making mRNA) and contains the genetic code for each cell
describe the nuclear envelope and its role
its a double membrane that surrounds the nucleus and it controls the entry and exit of materials and contains reactions taking place
what is the nuclear envelope continuous with?
the endoplasmic reticulum
describe the nuclear pores and its role within the nucleus
has 3000s pores per nucleus, each 40-100nm in diameter and it allows the passage of large molecules such as mRNA
describe the nucleolus and its role?
it makes ribosomal RNA and assembles ribosomes. may be more than 1 nucleolus in a nucleus
describe the nucleoplasm and its role within the nucleus
granular, jelly-like substance that makes up the bulk of the nucleus
desribe the chromosomes and its role within the nucleus
found in nucleus, protein-bound linear DNA
draw the structure and state the function of the mitochondria
site of aerobic respiration, site of ATP production and where DNA codes for enzymes needed in respiration
describe the mitochondria
usually rod-shaped 1-10nm in length
explain the mitochondrias double membrane and its role
has an outer and inner membrane that controls the entry and exit of materials
describe the cristaes?
the inner membrane is folded to make cristae. which can extend across the whole width of the mitochondrion
describe the cristaes role in the mitochondria
provides a large SA for attachment of enzymes and other proteins involved in respiration
describe the matrix and its role in the mitichondrion?
contains proteins, lipids, ribosomes and DNA that allow the mitochondria to control production of own proteins. many enzymes involved in respiration are found in the matrix
draw and state the function of chloroplasts
main site of photosynthesis
describe the role of the double membrane in the chloroplasts
the double plasma membrane surrounds the organelle it is highly selctive in what it allows to enter/exit the chloroplasts
describe the thylakoids and its role?
thylakoids contain a green pigment (chlorophyll). some thylakoids have tubular extensions that join up with thylakoids in adjacent grana
describe the grana and its role?
stacks of 100 disc-like structures called thylakoids where 1st stage of photosynthesis takes place (light absorbtion)
describe the stroma and its role?
fluid filled matrix where 2nd stage of photosynthesis takes place (synthesis of sugars) and contains enzymes to make sugars for photosynthesis
why do granal membranes have a large SA?
for attachment of enzymes, chlorophyll and electron carriers
why do chloroplasts contain both DNA and ribosomes?
quickly make proteins needed for photosynthesis
draw and state the function of the rough endoplasmic reticulum
Packages transports modified proteins
describe the ribosomes and its role within the RER?
ribosomes are present on the outer membrane. they provide a large SA for synthesis of proteins and glycoproteins also provide a pathway for the transport of materials especially proteins throughout the cell.
what are the cisternae?
folded memebranes
draw and state the function of the smooth endoplasmic reticulum
synthesises, stores and transports lipids and carbohydrates
describe the structure of the SER
folded membranes-cisternae, no ribosomes
what type of cells have lots of SER and RER
secretory cells e.g epithelial and liver cells
when are lysosomes formed?
when the vessicles produced by the golgi contain enzymes such as protease and lipases
draw state each function of the lysosome?
- hydrolyse material injested into cellels
- release enzymes to the outside of the cell (exocytosis) to destroy material around cell
-digest worn out organelles so that the useful chemicals theyre made out of can be reused - completely break down cells after they have died (autolysis)
describe the lysosome and the enzymes within
lysosomes contain lysozymes enzymes that hydrolyse the cell wall of certain bacteria
how many enzymes can be in a lysosome?
as many as 50
lysosmes are abundant in…?
secretory cells
draw and state the many functions of the golgi
- add carbohydrates to proteins to form glycoproteins
- produce secretory enzymes
- secret carbohydrates
- transport, modify store lipids
- form lysosomes
how are proteins passed through the golgi apparatus?
stage 1:
the proteins and lipids are passed through golgi apparatus through a strict sequence
stage 2 :golgi
the golgi modifies the proteins often adding other components e.g carbohydrates
stage 3:golgi
then labels them allowing them to be sent to their accurate destinations
stage 4: golgi
once sorted modified proteins and lipids are transported to golgi vessicles
stage 5 : golgi
these vesicles may move to their cell surface where they fuse with the membrane and release contents
in which cells are the golgi especially well developed in?
secretory cells
draw and describe the function of the ribosomes?
site of protein synthesis
what are ribosomes made up of?
protein and ribosomal RNA
describe the larger version of ribosomes?
- 80s
- found in eukaryotic cells
-around 25nm in diameter
describe the smaller version of ribosomes?
- 70s
- found in prokaryotic cells, mitochondria, chloroplast
-much smaller
draw and state the function of the cell wall?
to provide mechanical/structural strength in order to prevent cells bursting under the pressure created by osmosis
describe the features of the cell wall and their roles?
in plant cells- made of microfibrils of polysaccharide cellulose
in animal cells - made up of chitin polysaccharide of nitrogen
- thin layer called middle lamella marks the boundry between adjacent cell walls and cements them together
draw and state the function of the vacoule?
- support herbaceous plants /woody plants by making cells turgid
-act as temporary stores of sugar and amino acids
-these pigments may colour petals to attract pollinating insects
describe the structure of the vacoule
Filled with fluid surrounded by a single membrane tonoplast
draw and state the function of the Tonoplast
Single membrane controls the exit and entry of materials
What is cell fractionation?
A means of studying different parts of a cell and investigating the function of organelles
What is homogenisation?
1st stage in cell fractionation it breaks open the cell/ releases organelles
Explain the homogenisation process?
- Cells are broken up by the homogenizer which releases organelles.
- Resistant fluid homeganate is then filtered to remove insoluble tissue and cellular debris
Before homegenation why does the tissue need to be placed into an ice cold isotonic buffer?
- Ice cold - slows down enzyme activity
- Isotonic - prevents shrinking or bursting of organelles by osmosis
- Buffer - prevents change in pH which would effect enzymes
Why do we need to filter our homogenate?
May contain cellular debris that has equal density as organelles
What is ultracentrifugation?
2nd stage of cell fractionation where homogenate is spun to separate organelles in a centrifuge
Explain how ultracentrifugation works
a.k.a differential centrifugation?
- The tube of filtrate is placed in a centrifuge and spun at a low speed
- The heavier more dense organelles is forced to the bottom of the tube forming a thin sediment pellet
- The fluid (supernatent) is removed/transferred into another tube , leaving just the sediment of the nuclei
- The remaining super agent is spun again at a faster speed where this time the sediment pellet formed contains the mitochondria
- This process is repeated by increasing the speed to remove the next dense/ heavier organelles
What type of cell is a bacteria cell?
Prokaryotic cell
What are the properties of prokaryotic cells?
Smaller cells, no membrane bound organelles, no nucleus cell wall made of murein
Draw structure of a prokaryote
The cell wall is made of…
Peptidoglycans (murein) rather than cellulose
Function of the cell wall?
Prevents bursting in hypertonic surroundings, maintains shape
What is the cell membrane and it’s role?
A double phospholipid layer which controls the passage of substances into and out of the cell
What is the nuclear zone and its function?
Folded/circular tight mass of DNA and RNA ,usually a singular strand contains nucleus acid with genetic information
What are ribosomes and explain their role in prokaryotes?
70s ribosomes main site of protein synthesis (translation)
What may some bacteria contain?
Plasmid , capsule and flagella
What is the flagella and it’s function?
A long fine projection made of the contractile protein called flagellin. responsible for locomotion, can be from one end of the cell or several around the cell
What are plasmids and their function?
Self- replicating small loops of DNA. Can be transferred between cells often responsible for antibiotic resistance transferral, useful in genetic engineering
What is the capsule and it’s function?
Made up of polysaccharides , protection against wbc, antibodies and other harmful environmental factors. also enables attachment to other objects
Explain how a light microscope works?
Illuminated by:
Focused by:
Maximum magnification:
Resolving power:
Specimens dead or living:
Specimen thickness:
Ease of preparation:
Cost of equipment:
Images colour:
Image dimension:
- Illuminated by light
- Focused by glass lenses
- x1500
- 200nm (can see cells but not details of organelles)
- both
- thin
- easy
- cheap
- coloured images
- 2D
Explain how a transmission electron microscope works?
Illuminated by:
Focused by:
Maximum magnification:
Resolving power:
Specimens dead or living:
Specimen thickness:
Ease of preparation:
Cost of equipment:
Images colour:
Image dimension:
- illuminated by a beam of electron
- focused by a condenser magnet
- x500,000
- 0.1nm or 1nm
- both
- had to be really thin to allow electrons to penetrate
- difficult
-expensive - black and white
- 2D
Why does the specimen appear darker or brighter in some areas?
Parts of the specimen that appear dark absorb electrons whereas the parts of the specimen which appear lighter allow electron to pass through it
Explain how a scanning electron microscope works?
Illuminated by:
Focused by:
Maximum magnification:
Resolving power:
Specimens dead or living:
Specimen thickness:
Ease of preparation:
Cost of equipment:
Images colour:
Image dimension:
- illuminate by a beam of electrons
- focused by an electron magnet
- x500,000
- 20nm
- specimen must be dead
- thin but not as thin as TEM
- difficult
- expensive
- black and white
-3D
Limitations of SEM and TEM?
- whole system has to be in a vaccum so living specimens cannot be observed
- complex ‘staining’ process required yet image is still not coloured
- specimen must be extremely thin (TEM)
- the image may contain artefacts
What’s the difference between SEM and TEM?
The SEM directs a beam of electrons onto surface of specimen from above whereas TEM a beam of electrons is penetrating it from above
Advantages of the electron microscope
- electron beam has a shorter wavelength so it has a higher resolution
- electrons are negatively charged so can be focused by an electromagnet
What is an eyepiece graticule?
A disc which allows the size of the specimen to be observed
What is an important rule of the eyepiece graticule?
The scale of the eyepiece graticule remains constant no matter what magnification the cells are viewed at
What is meant by the term calibration?
Fixing know points and constructing a scale between them
To calibrate an eyepiece graticule what do we use..?
What does a stage micrometer show?
- a special microscope slide - stage micrometer
- true lengths
DONE!!
