Cell Structure Flashcards
structure of eukaryotes, structure of prokaryotes & viruses, methods of studying cells & all cells arise from other cells
What are eukaryotes and prokaryotes?
Eukaryotic: DNA is contained in a nucleus, contains membrane-bound specialised organelles e.g. plant, animal and fungi
Prokaryotic: DNA is ‘free’ in cytoplasm, no organelles e.g. bacteria and archaea
Structure of the Nucleus?
- large membrane-bound organelle, surrounded by nuclear envelope which contains many pores
- nucleus contains chromosomes and 1 or more structure called a nucleolus (assembles cell’s ribosomes)
The function of a nucleus?
- houses the cell’s genetic material/DNA, and is also the site of synthesis for ribosomes (nucleolus) = the cellular machines that assemble proteins
Structure of the cell-surface membrane?
- found on the surface of animal cells and just inside cell wall of others (plants)
- phospholipid bilayer with intrinsic and extrinsic proteins
Function of the cell-surface membrane?
- regulates movement of substances in and out of cell
- also has receptor molecules on it, which allow it to respond to chemicals like hormones
Structure of mitochondrion?
- oval shaped
- double membrane (inner one folded to form cristae and inside is matrix which contains enzymes involved in respiration)
Function of mitochondrion?
- site of aerobic respiration, where ATP is produced
- Found in large numbers in cells that are v actice and require a lot of energy
Structure of the Golgi Apparatus?
- group of membrane-bound fluid-filled flattened sacs
- vesicles are often seen at edge of sacs
Function of Golgi Apparatus?
- processes and packages new lipids and proteins.
- also makes lysosomes
Structure of Golgi Vesicle?
- membrane-bound
- small fluid-filled sac in cytoplasm, and produced by golgi apparatus
The function of Golgi vesicle?
- stores lipids and proteins made by the Golgi apparatus and transports them out of the cell (via cell-surface membrane)
Structure of the lysosome?
- type of golgi vesicle
- round organelle surrounded by membrane
- no clear internal structure
Function of the lysosomes?
- contains lysozymes (digestive enzymes)
- lysozymes kept separate from cytoplasm by surrounding membrane
- can be used to digest invading cells or break down worn-out components of cell
Structure of ribosomes?
- very small organelle that floats freely in cytoplasm or is attached to rough endoplasmic reticulum
- made up of proteins and RNA
- not surrounded by a membrane
Function of ribosomes?
- site where proteins are made
Structure of rough endoplasmic reticulum (RER) ?
- a system of membranes enclosing a fluid-filled space
- surface covered w ribosomes
Function of rough endoplasmic reticulum (RER) ?
- folds and processes proteins that have been made at the ribosomes
Structure of smooth endoplasmic reticulum (SER) ?
similar to RER but no ribosomes
Function of SER?
synthesizes and processes lipids
Structure of chloroplast?
- small, flattened structure found in plants and algal cells
- surrounded by double membrane
- Inside the chloroplast are stacks of thylakoids, called grana, as well as stroma, the dense fluid inside of the chloroplast
Purpose of thylakoids
- thylakoids contain chlorophyll (which absorbs light) that is necessary for the plant to go through photosynthesis
Function of chloroplast?
- site of photosynthesis takes place
- some parts happen in the grana and others in the stroma (thick fluid)
Structure of the cell wall?
- rigid structure that surrounds cells in plants and fungi
- in plants/algae it’s made mainly of cellulose
- in fungi, it’s made of chitin (polysaccharides)
Function of cell wall?
- provides strength to the cell, which helps protect the cell against physical damage
- prevents it from changing shape
Structure of cell vacuole?
- membrane-bound organelle found in cytoplasm of plant cells
- contains cell sap - weak solution of sugars & salts
- surronding membrane called tonoplast
What is tonoplast?
- cytoplasmic membrane surrounding the vacuole
- separating the vacuolar contents from the cytoplasm in a cell
Function of the vacuole?
- helps maintain pressure inside cell and keep cell rigid, stops plant wilting
- also involved in isolation of unwanted chemicals inside the cell
Organelles that plant cells contain & others don’t?
- cellulose cell wall with plasmodesmata (‘channels’ for exchanging substances with adjacent cells)
- vacuole (compartment that contains cell sap)
- chloroplast
Name the parts of a bacteria cell
- cytoplasm
- plasma membrane
- cell wall
- capsule
- plasmids
- circular DNA
- flagellum (pl. flagella)
How are specialized cells organized?
into tissues, tissues into organs & organs in organ systems
e.g.
tissue - muscle tissue
organs - animal heart
organ systems - female reproductive system - includes uterus, ovaries, mammary glands & breasts
Compare prokaryotes and eukaryotes
- prokaryotic cells are smaller
- prokaryotic cells are unicellular, eukaryotic cells are often multicellular
- prokaryotic cells have no nucleus or membrane, eukaryotes have nucleus & membrane-bound organelles
- in prokaryotes, DNA is circular w/o proteins, in eukaryotic cells DNA linear & associated with protein to form chromatin
- in prokaryotes, cell division by binary fission, in eukaryotes cell division is by mitosis or meiosis
- in prokaryotes reproduction is asexual, in eukaryotes, it’s sexual or asexual
- in prokaryotes there’s a huge variety of metabolic pathways but common metabolic pathways for eukaryotes
- in prokaryotes ribosomes are small (70S), in eukaryotes ribosomes are large (80S)
Cells of prokaryotes and eukaryotes?
- prokaryotes are simple, single-celled organisms
- eukaryotes are complex multicellular organisms
Examples of eukaryotes?
animal, plant, fungi and algae cells
Example of prokaryotes?
Bacteria
What kind of organism are viruses?
Acellular, they’re not cells
How do viruses replicate?
- being non-living, viruses don’t undergo cell division
- they use host cells to replicate themselves
Describe how Viruses Replicate
- viruses use host cells
- use their attachment protein to bind to complementary receptor proteins on the surface of host cells (different viruses have different attachment proteins)
- inject their own DNA (or RNA) into host cell, which provides instructions for metabolic processes of host cell to produce viral components, which are then assembled into new viruses
Describe the structure of a virus
- smaller than bacteria
- contains nucleic acids (e.g, DNA or RNA) as their genetic material
- attachment proteins vital for virus to identify and attach to host cell
- nucleic acid enclosed within protein called CAPSID
Describe Mitosis cell structure practical (RP 2)
- cut root tip (e.g. from onion)
- put root tip in HCl (1 mol dm-3) and in water bath (60 degrees C)
- rinse root tip w/ cold water and dry/blot
- place on microscopic slide (2mm of tip) and spread w/ mounted needle
- Add a stain (touidine blue O) to see cells
- place cover slip on top to sqaush cells
- place under microscopic microscope
Give 3 controlled variables to ensure similar root growth in plants (with reasons) in mitosis practical
- all plants of same age (so same time for cell divisions)
- all plants given same watering (so same amount of water for cell expansion)
- all plants given same light (same rate of photosynthesis)
Why is a root tip used in mitosis practical?
it’s where mitosis occurs
why is a stain used in mitosis practical?
to distinguish chromosomes - not visible w/o stain
why is root tip firmly squashed?
make tissue thinner and allow light to pass through it
What could make results different from others in mitosis practical?
- temp
- age of root tip
- chance
- genetic differences / different type of onion (or garlic)
- water availability
Is interphase part of mitosis?
No
Why is mitosis needed?
- growth of multicellular organisms
- repairing damaged tissues
What happens in mitosis?
parent cell divides to produce two genetically identical daughter cells
What happens in the cell cycle?
- consists of a period of cell growth and DNA replication called interphase
- Mitosis happens after that
Interphase is subdivided into what?
- 3 separate growth phases
G1 gap phase 1
S synthesis
G2 gap phase 2
What happens in Gap phase 1?
cell grows and new organelles & proteins made
What happens in synthesis?
cell replicates it’s DNA, ready to divide by mitosis
What happens in Gap phase 2?
cell keeps growing & proteins needed for cell division are made
What is mitotic index?
proportion of cells in a population undergoing mitosis
How do you calculate mitotic index?
cells undergoing mitosis (P+M+A+T)/ total no. of cells (I+P+M+A+T) X 100
How is a tumor formed?
- if mutation occurs in gene that controls cell division, cells can grow out of control
- cells keep dividing to make more & more cells to form a tumour
What’s a tumor?
a group of abnormal cells
What is cancer?
a tumour that invades surrounding tissue
How do drugs used to treat cancer (chemotherapy) work
- by disrupting the cell cycle:
- preventing DNA from replicating
- inhibiting metaphase stage by interfering with spindle formation
The issue with drugs used to treat cancer?
- the drugs also disrupt cell cycle of normal cells
What happens in interphase?
- DNA replicates in cell
- and chromosomes become visible
What happens in prophase?
- chromosomes condense getting shorter & fatter - stay together due to CENTROMERES
- Nuclear envelope disintegrates
- Nucleolus disappears
What happens in metaphase?
- spindle forms
- chromosomes line up on centre of the cell
What happens in anaphase?
- spindle fibres attached to CHROMATIDS contract
- chromatids are pulled towards opposite poles of cell
What happens in Telophase
- cytoplasm begins to divide & nuclear envelope reforms
- spindle fibres disintegrate and cytoplasm dividesin CYTOKINESIS
- so 2 genetically identical daughter cells formed
Differences between meiosis and mitosis
- Mitosis produces diploid cells, meiosis produces haploids cells
- Mitosis produces genetically identical daughter cells, meiosis produces genetically different daughter cells
- Mitosis produces 2 daughtr cells, meiosis produces 4
Random Q: What 2 things give meiosis genetic variation?
- independent assortment
- crossing over
Describe the process of binary fission?
- circular plasmid loops replicated lots & Circular DNA strand replicated once
- DNA loops drawn to opposite poles of cell
- cytoplasm divides, new cell walls begin to form
- 2 new daughter cells formed and have 1 copy of circular DNA but variable no. of copies of plasmids
Describe the ribosome in a bacterial cell
- smaller than those in eukaryotes
Describe the circular DNA in a bacterial cell
- possesses genetic info for replication of bacterial cells
Describe the cell wall in bacterial cells
- made up of MUREIN - polymer of polysaccharides and peptides (It's a glycoprotein) - acts as a physical barrier that protects bacteria
Describe the capsule in bacterial cells
- bacteria protect themselves by secreting capsule of mucilaginous SLIME around this wall
Describe the cells surface membrane in a bacterial cell?
- made up of lipids & proteins
- controls movements of substances in & out of cell
Describe the plasmid in a bacterial cell?
- small loops of DNA
- possesses genes that may aid survival of bacteria in adverse conditions e.g. produces enzymes that break down antibiotics
Describe the flagellum in a bacterial cell?
- long hair like structure
- rotates to make prokaryotic cells move
What is magnification?
how many times larger the image is compared to the object
mag = image size/ actual size
(I AM)
What’s resolution?
-ability of a microscope to distinguish 2 adjacent structures as separate
What does a high resolution result in?
- better clarity and detail of the image
Name the two types of microscopes
- optical (light) microscopes
- electron microscopes (SEM and TEM)
How does an optical microscope work?
Light focused on small area of thin specimen
Lenses magnify image
(individual cells usually transparent and so coloured w/ special stains to make distinguishable)
Specimen in optical microscope:
can be alive
What does staining do to cells in optical microscopes?
kills them
Max resolution and magnification of optical microscopes?
0.2 micrometres
x 1500 mag
What can be seen in optical microscope?
Nucleus and mitochondria
How does Electron microscope work?
- uses beam of electrons instead of beam of light
- this allows for high magnfication & resolving power (resolution)
Max resolution and magnification of electron microscopes?
0.002 micrometres
x 150, 0000 mag
What does SEM and TEM stand for?
- Scanning electron microscopes
- Transmission electron microscopes
Describe scanning electron microscopes
- a beam of electrons passes
across the surface and scatter. - the pattern of scattering builds up a 3D image depending on the contours of the specimen
Two differences between SEM and TEM
- specimens in SEM do not have to be thin like in TEM
- Resolution is lower in SEM than in TEM
Describe Transmission electron microscopes
- elecron beam penetrates cells & provide detail of cell’s internal structures
What do TEMs use?
- electromagnets to focus electron beam (they’re high resolution microscopes)
Advantage of TEM?
High resolution so can see internal structures of organelles like chloroplast
What’s the point of cell fractionation?
- separates organelles according to size to allow them to be studied in an electron microscope
Stages of cell fractionation
- Homogenisation
- Filtration
- Ultracentrifugation
What happens in homogenisation?
- tissue sample blended (homogenised) using blender to break cells under specific conditions
Specific conditions of homogenisation and why?
- ice cold (reduces enzyme activity that might damage organelles)
- isotonic solution (prevents osmosis that could shrink or burst organelles - no osmosis takes place in isotonic solution)
- buffered solution (avoids damaging protein structures)
What happens in filtration of cell fractionation?
- tissue sample filtered into gauze - gauze separates large components from small organelles
- organelles filtered into tubes to be fractionated using ultracentrifugation
What happens in ultracentrifugation of cell fractionation?
- sample spun at low speed in a centrifuge
- each tube balanced w/ another tube directly opposite for centrifuge to work properly
- cell debris (e.g. cell walls) forms pellet at bottom of tube, leaving supernatant (a liquid) above it that contains the organelles
- supernatant poured off & centrifuged at higher speed to separate next heaviest organelles
- repeated as increasingly higher speeds to separate each fraction
What does centrifugation do?
- centrifuge spearates sample into fractions (heavier organelles forced to bottom of tube, lighter organelles move towards top)
Last process of centrifugation?
- supernatant poured off & centrifugation at higher speed to separate next heaviest organelles
- repeated as increasingly higher speeds to separate each fraction
Heaviest to lights organelles:
- Nucleus
- Chloroplasts
- ER
- mitochondria
- lysosomes
- ribosomes
Limitations of TEM?
- whole system must be in a vacuum therefor living organisms can’t be observed
- specimen must be extremely thin
- image may contain artefacts (things that result from the way the specimen is prepared)
- complex staining process required & even then image not in colour
What’s a graticule?
- glass disc that is placed in eyepiece of microscope
- scale etched onto glass disc
- scale typically 10 mm long with 100 sub-divisions
- scale visible when looking down eyepiece of a microscope
How to calibrate a graticule?
- Place a stage micrometer on the stage of the microscope
- line up one of the divisions on the eyepiece graticule with a fixed point on the stage micrometer.
- count number of divisions on eyepiece graticule that correspond with a set measurement on stage micrometer
- Calculate the distance in micrometres of one division on the eyepiece graticule.
Conversions of millimetre to micrometer
divide by 1000
Types of measurements/ units?
millimetres, micrometres, nanometres
Compare and contrast DNA in eukaryotic cells and prokaryotic cells
- DNA in mitochondria/chloroplast similar (structure) to DNA in prokaryotes
- Eukaryotic DNA is linear
- Eukaryotic DNA contains introns, prokaryotic DNA doesn’t
- Eukaryotic DNA is linear, prokaryotic DNA circular
- Eukaryotic DNA is associated with proteins/histones, prokaryotic DNA is not
State 1 way to calculate the area of a plant leaf
- draw around leaf on graph paper and count squares
contrast how an optical microscope and a transmission electron microscope work
- TEM use electrons, optical uses light
- TEM allows greatER resolution
- so, with TEM smaller organelles can be observed
- TEM can only view dead/dehydrated specimens and optical can be observed
- TEM doesn’t show colour and optical can
- TEM requires thinnER specimen
- TEM requires a more complex/time-consuming preparation
- TEM focuses using magnets and optical (glass) lenses
suggest ways to improve the quality of a scientific drawing
- don’t use shadowing
- don’t use sketching/use single lines
- add (more) annotations
- don’t cross label lines
- add magnification/scale (bar)
Describe how you would use cell fractionation techniques to obtain a sample of chloroplasts from leaf tissue. Do not include in your answer information about any solutions.
[3 marks]
- Macerate / homogenise / blend / break tissues
/ cells (in solution); - Centrifuge;
- At different / increasing speeds until
chloroplast fraction obtained;
Give three structures found in the prokaryotic cells but not in the eukaryotic cells
Plasmid DNA
flagellum
capsule
How would you calculate the number of cells produced by mitosis
No (Number of cells beginning with) x 2n (2 to the power of ‘the number of divisions’)
e.g. bacteria culture of 3 cells underwent 6 cell divisions. Assuming no deaths to limiting factors, calculate the number of cells in the culture after the division
3 x 2(power of 6) = 192 cells
