Cell Structures Flashcards
List the units of length from largest to smallest (with symbol and equivalent in metres)
Describe the one limitation of a light microscope
- long wavelength of light = only distinguish 2 objects if they are 0.2µm apart
How can the limitations of a light microscope be overcome
electron microscope
- uses beam of electrons because of their shorter wavelengths
- therefore you can distinguish objects 0.1nm apart
What is the object
The material under the microscope
What is the image
The appearance of the material when viewed through the microscope
What is the magnification
How many times bigger the image is when compared to the object
What is the equation to work out size of image
Size of image = magnification x Size of real object
What is the resolution, or resolving power
the minimum distance apart that 2 objects can be in order for them to appear as separate items
What does the resolving power depend on
- The wavelength or form of radiation used
What is the resolving power for a typical light microscope
0.2 µm
—> closer than that = will appear as a single item
Does increasing magnification always increase resolution
No
what is cell fractionation
the process where cells are broken up and the different organelles they contain are separated
why is potato homogenised using a cold, isotonic buffer
- Cold: reduce enzyme activity that could break down organelles
- Isotonic: stop water levels being too high/low which would cause organelles to burst/shrink
- buffered: so pH doesn’t fluctuate (changes in pH could alter structure of organelles or affect functionality of enzymes)
what are the 2 stages of cell fractionation
- Homogenation
- Ultracentrifugation
What happens during Homogenation
- cells are broken up by homogeniser (blender)
- releasing organelles from cells
- the resultant fluid = homogenate
- which is then filtered to remove any complete cells and large pieces of debris
where does ultracentrifugation happen
fragments in homogenate are separated in a machine called a centrifuge
what does a centrifuge do
spins tubes of homogenate at high speeds in order to create a centrifugal force
describe the ultracentrifugation process for animal cells
- Tube of filtrate is placed in centrifuge and spun at a slow speed
- heaviest organelles (nuclei) are forced to the bottom of the tube, forming a thin sediment/pellet
- fluid at top of tube (supernatant) is removed, leaving just the sediment of nuclei
the removed supernatant is transferred to another tube and spun faster than before - next heaviest organelle (mitochondria) are forced to the bottom of the tube
- This process continues in a way that at each increase in speed the next heaviest organelle is sedimented and separated out.
what is the speed of centrifugation/ revolutions min-1 for:
- nuclei to be separated
- mitochondria to be separated
- lysosomes to be separated
- nuclei: 1 000
- Mitochondria: 3 500
- Lysosomes: 16 500
why has cell fractionation and ultracentrifugation been useful
allowed detailed study if structure and function or organelles by showing what isolated components do
why are light microscopes considered to have a poor resolution
light has a relatively long wavelength
what are the 2 main advantages of electron microscopes
- electron beam has a shorter wavelength and the microscope can therefore resolve objects well = it has a high resolving power
- electrons are - charge = the charged beam can be focused using electromagnets
what is one of the main disadvantages of an electron microscope
Because electrons are absorbed or deflected by the molecules in the air, a near vacuum has to be created within the chamber of the electron microscope
what are the 2 types of electron microscopes
- Transmission electron microscope (TEM)
- Scanning electron microscope (SEM)
How does a TEM work
- electron gun produces a beam of electrons, which is focused onto the specimen by a condenser electromagnet
- the beam passes through a thin section of the specimen
- parts of the specimen absorbs electrons and therefore appear dark, others allow it through so appear bright
- this produces an image on a screen which is photographed to produce a photomicrograph
What is the maximum resolving power of a TEM, why this may not be easily achieved
Resolving power = 1nm
- difficulties preparing the specimen limit the resolution that can be achieved
- a higher energy electron beam is required and it may destroy the specimen
What are the 4 main limitations of a TEM
- whole system must be in a vacuum = living specimen cant be observed
- complex ‘staining’ process is required, even if the image isn’t in colour
- specimen must be thin
- artefacts may appear on finished photomicrograph that aren’t apart of the natural specimen, therefore we cant assume what we see on a photomicrograph really exists in that form
what are artefacts
things that result from the way the specimen is prepared
–> appearing on the finished photomicrograph
Why must specimen be thin in the TEM
to allow the electrons to penetrate
Does a TEM produce a 3D or 2D image
2D
- we can get over this by creating a 3D image with separate images of different sections of the specimen
–> however this is complicated
How does a SEM function
- directs a beam of electrons onto surface of specimen from above
-beam is passed back and forth across the specimen in a regular pattern - electrons are scattered by specimen
- the pattern of scattering = the contours on specimen’s surface
- we can create a 3D image by a computer analysing these scatterings + secondary electrons produced
Hans and Zacharias Johnson
→ They were eyeglass lens grinders
→ used 2 small convex lenses, found they could magnify to 9x (short focal length)
Robert Hooke
70 years later = created his own version from Onsen’s design to study cork slice = discovering cells
Antony van Leeuwenhoek
Antony van Leeuwenhoek designs hand help microscope
→ can magnify 270 x
→ discovers bacteria and human cells
Richard Zsigmondy
Invents ultra microscope
How do you prepare a slide
- Specimen has to be as thin as possible = let light through
- prepare dry/wet mount
—> stains are used with wet mounts
How to you prepare a wet slide
- Use a pipette, place drop of water onto the middle of a clean microscope slide.
- Place specimen into the water drop using tweezers.
-Place a cover slip on top of the specimen.
(Extra care needed because of trapped air bubbles underneath) - Stand the cover slip upright on its edge over the specimen, then using your tweezers, carefully lower it into place.
- Add any necessary stains after the cover slip is in position.
- Place a drop of the stain at one side of the cover slip.
- Place a paper towel against the edge of the opposite side (drawing the stain under the cover slip and across the specimen)
- You may need to add another drop to ensure the specimen is fully stained, or you may wish to repeat this process with a different stain.
How do you prepare a dry mount
- Place your specimen in the middle of a clean microscope slide using tweezers.
- Place a cover slip on top of the specimen.
- The cover slip will hold the specimen in place and prevent it from getting damaged.
How can we help the image form
Special stains, usually dyes for light microscopy, can be used on specimens like this to help the image form.
What are the 2 most common stains in microscopy
- Common stains include eosin and methylene blue.
- Eosin stains the cytoplasm pink
- while methylene blue stains DNA and RNA blue.
Can multiple stains be used together
Yes - produces best imagery
What is the radiation source of a light microscope, TEM, SEM
- light
- electrons
- electrons
What is the wavelength of a light microscope, TEM, SEM
- 400-700nm
- 0.005nm
- 0.005nm
What is the lens of a light microscope, TEM, SEM
- glass
- electromagnetic
- electromagnetic
What is the specimens used in a light microscope, TEM, SEM
- living or non living supported on glass slide
- non-living supported on a small copper grid in a vacuum
- non-living supported on a metal disc within a vacuum
What is the maximum resolution of a light microscope, TEM, SEM
- 200nm
- 1nm
- 10nm
What is the maximum magnification of a light microscope, TEM, SEM
- 1000 x
- 250 000 x
- 100 000 x
What is the different stains can be used on a light microscope, TEM, SEM
- coloured dyes e.g. methylene blue
- heavy metals
- coated with carbon or gold
What type of image does a light microscope, TEM, SEM produce
- 2D can be coloured
- 2D monochrome
- 3D monochrome
How can we measure the size of objects
Using an eyepiece graticule
What is the graticule
- A glass disc that is placed in the eyepiece of a microscope
- a scale is etched onto this disc
- its typically 10mm long, divided into 100 sub-divisions
- you can see this scale when looking down the eyepiece
Can you directly measure the size of objects under a microscope’s objective lens using an eyepiece graticule
- no
- each objective lens will magnify to a different degree
- the graticule must first be calibrated for a particular lens
- once calibrated in this way, it can remain in this position for future use, provided the same objective lens is produced
How to you calibrate the eyepiece graticule
- use a stage micrometer (special microscope slide)
- this slide has a scale etched onto it that is 2mm long, its smallest subdivisions are 0.01nm
How many units on the graticule scale is 10 units on the micrometer scale
- 40
- therefore 1 unit on micrometer scale = 4 units on graticule scale
- as each unit on the micrometer scale = 10 micrometers, each unit on the graticule:10/4= 2.5 micrometers
If an objective lens magnifying x40 gives a calibration of 25 micrometers per graticule unit, what would an objective lens magnifying x400 mean a graticule unit is equivalent to
25 micrometers / 10 = 2.5 micrometers
What are the general principles for biological drawing
- use sharp pencil only
- use clear, continuous lines
- don’t use any form of shading
- accuracy is paramount - draw what you observe not think
- feint sketching is helpful
- using a magnifying glass or illuminating dissections is useful
- make drawing scaled right
- correct mistakes
- include a title and scale
What are the rules for labelling for biological drawings
- sharp pencil
- label all relevant structures and tissues
- use a ruler for label lines and scale bars
- label lines should touch the subject
- arrange labels neatly (don’t cross-over)
- labels are written horizontally
- title
- scale bar
What are the rules for scale and magnification for biological drawings
- give indication of scale and magnification
- actual sizes are impossible to tell from just a drawing
- if scale and magnification aren’t given = clarify if its a low or high power lens used
- PUT ACTUAL MAGNIFICATION ACHIEVED BY COMBINED EYEPIECE AND OBJECTIVE LENS JUST BELOW THE TITLE
What are the differences between high and low power drawings
- Drawings of cells are typically made when visualizing cells at a higher magnification power,
whereas - plan drawings are typically made of tissues viewed under lower magnifications (individual cells are never drawn in a plan diagram)
What are the guidelines for drawing low power drawings
- draw all tissues and completely enclose each tissue by lines
- don’t draw individual cells
- accuracy is important
What are the guidelines for high power drawings
- Draw only a few representative adjacent cells (3 is sufficient to show enough detail)
- Don’t shade in nuclei - just draw the outline. Similarly with nucleoli
Is this a low power drawing or a high power drawing
Low power
Is this drawing a high or low power drawing
High power
What is the Nucleus’ function
- control centre of cell through production of mRNA and tRNA and hence protein synthesis
- retain the genetic material of the cell in the form of DNA and chromosomes
- manufacture ribosomal RNA and ribosomes
Describe the structure of the nucleus
- Largest organelle
- Spherical
- Dark patches=chromatin
- Surrounded by nuclear envelope
- Composed of 2 fluid filled membranes
- Has nuclear pore-allows large molecules through
- Nucleolus inside
Do prokaryotic cells have a nucleus
No
Why is the nucleus the largest organelle
contains structures like the nucleolus and nuclear envelope that require space to carry out their functions.
What is the nuclear envelope’s function
- double membrane that surrounds the nucleus
- controls the entry and exit of materials in and out of the nucleus
- contains the reactions taking place within it
What is the structure of the nuclear envelope
- its outer membrane is continuous with the endoplasmic reticulum of the cell
- often has ribosomes on its surface
Describe the structure of Nuclear pores
- there are typically around 3000 pores in each nucleus
- each 40-100 nm in diameter
What is the function of nuclear pores
Allow the passage of large molecules, such as messenger RNA, out of the nucleus
What is the nucleoplasm
The granular jelly-like material that makes up the bulk of the nucleus
What are chromosomes made out of
Consist of protein-bound, linear DNA
Describe the structure of nucleolus
- Small spherical region within the nucleoplasm
- there may be more than 1 nucleolus in a nucleus
What is the function of the nucleolus
It manufactures ribosomal RNA and assembles the ribosomes
Describe the structure of centrioles
Small protein tubes of microtubules.
Describe the function of centrioles
Form fibres in cell division known as spindles which separate chromosomes
What stage of cell division is where centrioles are involved
During prophase
Explain why centrioles play an important role
They organise microtubules that serve as the cell’s skeletal system
Describe the structure of the mitochondrion
- rod shaped and 1-10 micrometers in length
- Made up of the following structures:
1. Double membrane
2. Cristae
3. Matrix
Describe the double membrane structure of the mitochondrion
- controls the entry and exit of material
- inner membrane is folded = form extensions called cristae
Describe the cristae structure of a mitochondrion
- cristae are extensions of the inner membrane, which in some species extend across the whole width of the mitochondrion
- large surface area: for attachment of enzymes and other proteins involved in respiration
Describe the matrix structure of the mitochondrion
- makes up the remainder of the mitochondrion
- contains protein, lipids, ribosomes and DNA (allows the mitochondria to control production of their own proteins)
- contains enzymes involved in respiration
What is the function of the mitochondrion
- site of aerobic stages of respiration (Krebs cycle and oxidative phosphorylation pathway)
- production of energy carrier molecule: ATP (from respiratory substances such as glucose)
- number/size of mitochondria and cristae are high in cells that have a high level of metabolic activity (therefore require good supply of ATP)
- e.g. Epithelial cells in intestine require lots of ATP for active transport
Describe the structure of chloroplasts
- vary in shape/size, typically disc-shaped
- 2-10 micrometers long and 1 micrometer in diameter
- consist of 3 main features
1. The chloroplast envelope
2. The Grana/thylakoids/chlorophyll
3. The stroma
Describe the chloroplast envelope structure of chlorplasts
- double plasma membrane that surrounds the organelle
- highly selective in what it allows to enter and leave the chloroplast
Describe the grana structure of chloroplasts
- stacks of up to 100 disc-like structures called thylakoids
- within the thylakoids is the photosynthetic pigment called chlorophyll
- some thylakoids have tubular extensions that join up with thylakoids in adjacent grana.
- The grana are where light absorption happens
Describe the stroma structure of chloroplasts
- fluid filled matrix where the 2nd stage of photosynthesis occurs (synthesis of sugars)
- within the stroma are a number of other structures, such as starch grains
How are chloroplasts adapted to their function
- granal membranes: large surface area for attachment of chlorophyll, electron carriers and enzymes that absorb light.
- fluid of stoma has all the enzymes for making sugar in 2nd stage of photosynthesis
- chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for proteinsynthesis
Where are chlorophyll molecules found
In the thylakoid membrane of the chloroplast
What is the benefit of the chloroplast having 2 membranes
- outer: freely permeable to small molecules
- inner: impermeable to ions and metabolites
Describe structure of Endoplasmic reticulum
- system of sheet-like membranes, spreading through the cytoplasm of the cell
- continuous with outer nuclear membrane
- the membranes enclose a network of tubules and flattened sacs called cisterna
What is the Rough endoplasmic reticulum’s structure and function
- ribosome present on the outer surface of membranes
1. Large SA: for synthesis of proteins and glycoproteins
2. Provide a pathway to transport materials (especially proteins) throughout the cell
What is the Smooth endoplasmic reticulum’s structure and function
- lacks ribosomes on surface + tubular in appearance
1. Synthesise, store and transport lipids and carbohydrates
Describe the structure of the Golgi apparatus
- similar to SER, but more compact
- contains a stack of membranes = makes up flattened sacs (Cisterna)
- receives proteins made in endoplasmic reticulum, modifies them (adding non-protein components)
- then it sorts them, then transports them to the Golgi vesicle
What is the functions of the Golgi apparatus
- form glycoproteins (add carbohydrates to proteins)
- produce secretory enzymes
- secrete carbohydrates
- transport, modify and store lipids
- form lysosomes
Describe the structure of Lysosomes
- spherical sacs surrounded by a single membrane
- formed when the vesicles (produced by Golgi) apparatus contain enzymes such as proteases and Lipases
- They contain enzymes = hydrolyse the cell walls of certain bacteria
What’s the function of the Lysosome
Hrda
- hydrolyse material ingested by phagocytise cells
- release enzymes to the outside of the cell (exocytosis) in order to destroy material around the cell
- Digest worn out organelle so that the useful chemicals they are made of can be re-used
- Completely break down cells after they have died (autolysis)
What are ribosomes
- small cytoplasmic granules found in all cells
2 types:
—> 80S - found in eukaryotic cells, is around 25nm in diameter
—> 70S - found in prokaryotic cells, mitochondria and chloroplasts, is slightly smaller - They have 2 subunits. Each contain ribosomal RNA and protein
Describe the structure of Ribosomes
- very small organelles in the cytoplasm may be bound to rough endoplasmic reticulum
- made of RNA and protein
- consist of 2 subunits
What is the function of Ribosomes
Protein synthesis
Describe cell walls structure
- consists of mircofibrils of the polysaccharides cellulose, embedded in a matrix
- considerable strength
- thin middle layer called lamella: marks boundary between adjacent cell walls and cements adjacent cells together
Describe the cell walls function
- provides mechanical strength in order to prevent the cell bursting under the pressure created by the osmotic entry of water
- allow water to pass along it and so contribute to the movement of water through the plant
- give mechanical strength to the plant as a whole
What are cell walls made of
Either:
- cellulose
- glycoproteins
- or mixture of both
Describe cell walls of fungi
- don’t have cellulose
- comprised of a mixture of a nitrogen-containing polysaccharide called chitin, a polysaccharide called glycan and glycoproteins
Describe the structure of a vacuole
- fluid filled sac with a single membrane called a tonoplast
- it contains a solution of mineral salts, sugar, amino acids, wastes and sometimes pigments such as anthocyanins
What is the function of a vacuoles
- support herbaceous plants, and herbaceous parts of woody plants, by making cells turgid
- The sugars and amino acids may act as a temporary food store
- the pigments may colour petals to attract pollinating insects
- storage of cell products
why do eukaryotes become specialised
to carry out specific functions
list the 10 organ systems
- Muscular system
- Skeletal system
- Circulatory system
- Nervous system
- Lymphatic system
- Respiratory system
- Endocrine system
- Digestive
- Excretory
- Reproductive
Where are all the cells in a human produced from
Mitosis divisions from the fertilised egg
- all of these cells contain the same genes
How does every cell become specialised
- every cell contains genes needed for developing into any one of the organisms cells
- only some of these genes are turned on (expressed) in one cell, at any one time
- different genes are switched on in each type of specialised cell, whilst the rest of the genes are switched off
What (as well as shape of cell) can vary between different cells
Number of organelles
—e.g.—> sperm cell has lots of mitochondria, but bone cell has very few
What is the definition of a tissue
A group of similar cells organised into a structural unit that serves a particular function
Give 2 examples of tissues (one from humans and one from plants)
- epithelial tissues
- xylem
What is the epithelial tissue
- found in animals
- consists of sheets of cells
- they line surfaces of organs and often have a protective or secretory function
- there is many different types, including those made up of thin, flat cells that line organs where diffusion takes place
—e.g.—> alveoli (of the lungs), and ciliates epithelium (lines a duct such as the trachea)
What are cilia used for
To mover mucus over the epithelial surface
What is the xylem
- occurs in plants
- made up of similar cell types
- transports water and mineral ions throughout plant
- also gives mechanical support
What is an organ
Combination of tissues that are coordinated to perform a variety of functions, with one predominant major function
Describe the different tissues that make up a stomach
- muscle tissue: churn and mix stomach contents (mechanical digestion)
- epithelium tissue: protect stomach wall and produce secretions
- connective tissue: hold together other tissues
Describe the different tissues that make up a leaf
- palisade mesophyll tissue: made up of palisade cells (carry out photosynthesis)
- spongy mesophyll tissue: adapted for gaseous diffusion
- epidermis tissue: protect leaf and allow gaseous diffusion
- phloem tissue: transport organic material away from the leaf
- xylem tissue: transport water and ions into the leaf
What is an organ system
Organs that work together as a single unit. They are grouped together to perform particular functions
Give three examples of organ systems in humans
- Digestive system: digests and processes food. 7 Organs = salivary glands, oesophagus, stomach, duodenum, ileum, pancreas, liver
- respiratory system: breathing + gas exchange. 3 organs = trachea, bronchi, lungs
- Circulatory system: pumps + circulates blood. 3 organs = heart, arteries and veins
What are the 2 main types of cells
- Eukaryotic
- Prokaryotic
Briefly describe a Eukaryotic cell
- larger
- have a nucleus bounded by nuclear membranes (nuclear envelope)
Briefly describe a prokaryotic cell
- smaller
- no nucleus or nuclear envelope
From the perspective of a comparison, describe a prokaryotic cell
- no true nucleus, only an area where DNA is found
- DNA isn’t associated with proteins
- some DNA in form of circular strands (plasmids)
- no membrane-bounded organelles
- no chloroplasts
- ribosomes are smaller (70S)
- cell wall made of murein (peptidoglycan)
- may have an outer mucilaginous layer called a capsule
From the perspective of a comparison, describe a Eukaryotic cell
- distinct nucleus, with clear nuclear envelope
- DNA is associated with proteins (called histones)
- no plasmids, DNA is linear
- membrane bound organelles (like mitochondria) are present
- chloroplasts present in plants/algae
- ribosomes are larger (80S)
- cell wall made of cellulose (or chitin in fungi)
- no capsule
What is the role of a cell wall in a bacteria cell
- physical barrier
- excludes certain substances
- protects against mechanical damage and osmotic lysis
What is the role of a capsule in a bacteria cell
- protects bacterium from other cells
- helps groups of bacteria to stick together for further protection
What is the role of a cell-surface membrane in a bacteria cell
- acts as a differentially permeable layer, which controls the entry and exit of chemicals
What is the role of a circular DNA in a bacteria cell
Possesses genetic info for replication of bacterial cells
What is the role of a plasmid in a bacteria cell
- Possesses genes that aid to survival of bacteria in adverse conditions
- e.g. produces enzymes that break down antibiotics
What is the size range of bacteria
0.1 to 10 micrometers in length
What is a bacteria’s cell wall made up from
Murein
What is murein
A polymer of polysaccharides and peptides
How do many bacteria further protect themselves
Secreting a capsule of mucilaginous slime around the cell wall
Where is the cell-surface membrane
Inside the cell wall
How do bacteria store food reserves
They store food as glycogen granules and oil droplets
What is the form of the genetic info in a bacterium
CIRCULAR STRAND OF DNA
- SEPARATE TO THIS: smaller circular pieces of DNA = plasmids
What can the plasmids help do
- allow bacterium to reproduce themselves independently
- give bacterium resistance to harmful chemicals, such as antibiotics
What is the primary function of plasmids
Used extensively as vectors in genetic engineering
What does the Pili help bacterium to do
Interact with other bacteria
What does the flagellum help
Mobility
Are Viruses living
- no
- they’re acellular (non-living) particles
What is the size of a virus like
- very small
- 20-300nm
How do bacteria multiply, describe this process
BINARY FISSION
- circular DNA replicates and attaches to cell surface membrane
- plasmids replicate if present
- CSM grows between DNA pinching and dividing the cytoplasm
- new cell wall forms
- identical daughter cell is produced
What is the difference between Gram negative and positive bacteria
- negative: has a plasma membrane, layer of peptidoglycan cell wall + another membrane
—therefore—> it doesn’t stain as brightly as Gram positive
—because—> harder to get to peptidoglycan layer
What are the different bacteria’s that metabolise carbon sources
- phototrophs (energy from light)
- organotrophs (energy from organic compounds)
- lithotrophs (energy from inorganic compounds)
What are the 3 processes for how bacteria exchange genetic info
- transformation
- transduction
- conjugation
What is quorum sensing
- bacteria give off auto inducers
- this is then picked up by other bacteria, triggers genes to release
- causing them to glow
What is the functions of the viral protein coat
- viral genome is enclosed within capsid
- main function of coast is to protect the viral RNA or DNA
- specific sites on the surface if this coat allow the virion to attach to the host cell
- the capsid also provides proteins that enable the virus to penetrate the host’s cell membrane
Briefly describe the structure of the lipid membrane on a virus
- The phospholipid molecules are arranged into two layers form a lipid bilayer.
- They are organized in such a way that the tails of the molecules in two layers face each other, while their heads are directed opposite
Where is the material that is used to form the lipid membrane for viruses derived from
Material is derived from the host cell that it has infected
—because—> it can’t produce its own
What organelles to viruses contain
None (acellular)
What do viruses contain
- nucleic acid
- Viruses are either a DNA virus or an RNA virus
—> this is the viral genome
Where is the viral genome kept
- enclosed within a protective protein coat (known as a capsid)
What is a capsid formed from
Subunits called capsomeres
Where is the protein coat assembled
At the ribosomes coating the RER
Do viruses undergo cell division
- they do not undergo cell division
- Instead: they infect a host cell, and use it to replicate themselves and to produce new viral particles
What are the 5 steps to viral replication
- Virus binds to host cell
- Virus injects nucleic acids
- Virus infects viral proteins
- New viruses release from host cell
- Host cell dies
Describe step 1 for viral replication: attachment
- Virus binds to host cell using its attachment proteins
- Viruses can have different attachment proteins, which means that different viruses infect different types of cells
Describe step 2 for viral replication: Penetration
- Once the attachment proteins of a virus attach to a host cell,
- the virus latches onto the cell and injects the host cell with its nucleic acids
Describe step 3 for viral replication: Biosynthesis
- Certain viruses can also inject unique viral proteins into the host cell
- these viral proteins help hijack the host cells to replicate the viral genomes and to make new viral proteins
- viruses can force the cell to give up using energy to make proteins and replicate DNA for cell
Describe step 4 for viral replication: Assembly
- once the host cell has produced a sizeable number of viral particles
- the viral particles will burst through the cell through a process called lyric release
- once they burst through the cell, the viruses will go on to infect other host cells
Describe step 5 for viral replication: Release
- Meanwhile, the original host cell is now dead
- because of a gaping hole in its cell membrane
Why is it that specialised cells that all contain the same genes, can differ in structure + function
Different genes are switched on and off in each of the specialised cells
What are the 2 types of epithelia
- squamous (flat) epithelium
- ciliates epithelium
What are the features of a squamous epithelium
- single layer, thin cells, closely packed, each attached to basement membrane
- cells very thin so nucleus often forms a bump
- provides short diffusion distance of r rapid exchange or absorption
Examples of squamous (flat) epithelium in the human body
- Alveoli of lungs (because they’re thin)
- walls of blood capillaries
- renal capsule of kidneys (glomerulus)
- Linings of duct, arteries and veins
What are the features of ciliates epithelium
-single layer, cube shaped cells or columnar (column-like) cells, attached to basement membrane
- Cilia, present on side of cell opposite basement membrane, move mucus or other material
Examples of ciliated epithelium in the human body
- upper respiratory tract (trachea, bronchi)
- Oviduct/Fallopian tube, uterus
What is produced by mitosis
- 2 daughter cells
- that have the same number of chromosomes as the parent cell and each other
What is produced from Meiosis
- 4 daughter cells
- each with half the number of chromosomes of the parent cell
What are the different stages involved with mitosis
IPMATC
- interphase
- Prophase
- Metaphase
- Anaphase
- Telophase
What happens during interphase
- It precedes Mitosis
- Spherical nucleus surrounded by a nuclear envelope
- chromosomes are uncoiled and therefore can’t be seen
- Cell growth + DNA and organelle replication takes place
What happens during prophase
- Chromosomes coil = visible
- each divided into identical chromatids held by centromeres
- The nucleus envelope breaks down and nucleolus disappears
- Spindle fibres develop from centrioles at poles and attach to centromeres
What happens during Metaphase
- Chromosomes align at the centre of the cell
- they are attached to the spindle by their centromere
What happens during anaphase
- centromeres divide, separating each pair of sister chromatids
- spindles contract, pulling chromatids to opposite poles of the spindle, centromere first
- energy is provided by mitochondria
What happens during Telophase
- chromatids reach opposite poles of spindle
- uncoil = get longer =disappear
- chromatids can now be called chromosomes
- Spindle fibres disintegrate
- nuclear envelopes develop around chromosome = now there’s 2 nuclei
- cytokinesis (started in anaphase) now finishes
What happens in cytokinesis
- cell organelles become evenly distributed around each nucleus
- cytoplasm begins to divide
- IN ANIMAL CELLS: called cleavage - since a furrow develops in the cell membrane, getting deeper until the cell splits
- IN PLANT CELLS: spindle fibres don’t disappear, BUT forms a structure called a Phragmoplast.
Describe what phragmoplasts are
- formed in plants during cytokinesis
- Many organelles congregate in this area + fluid filled vesicles bud off from the Golgi apparatus (containing material needed to build new cellulose wall)
- The vesicles join together to form a cell plate which grows across the middle - eventually splitting into the 2 daughter cells
- in certain regions, the vesicles don’t fully fuse, leaving a cytoplasmic connection called a plasmodesma
How is cell division done in prokaryotic cells
Binary fission
Describe the different stages in binary fission
- circular DNA molecule replicates and both copies attach to the cell membrane
- plasmids also replicate
- cell membrane grows between the 2 DNA molecules and begins to pinch inward, dividing the cytoplasm into 2
- new cell wall forms between the 2 molecules of DNA (original cell —> 2 identical daughter cells)
- each daughter cells has a single copy of the circular DNA and a variable number of copies of the plasmids
Why is mitosis important
- Growth
- repair
- reproduction
Why is mitosis important for growth
- 2 haploid cells (sperm and an ovum) fuse together to form a diploid cell
- if the new organism is to resemble its parents, all the cells that grow from the original cell must be genetically identical identical
- Mitosis ensures this because daughter cells = identical to parent cells
Why is mitosis important for repair
- If cells are damaged or die its important that the new cells produced have an identical structure and function to the ones that have been lost
Why is mitosis important for reproduction
- Single-called organisms divide by mitosis to give 2 new organisms
- Each new organism is genetically identical to the parent organism
Suggest an advantage and a disadvantage of having offspring that are genetically identical to their parents
- ADV: as genetic make up of the parent has enable it to survive and reproduce, if the offspring has the same genetic make up, they are also likely to survive and reproduce
- DADV: genetic variety is limited - if environmental conditions changes the species may not have individuals with the necessary genes to survive in the new conditions. It could fail to adapt and become extinct
What are the 3 stages too the cell cycle
- Interphase (occupies most of cell cycle) (known as resting phase = no division takes place)
- Nuclear division (nucleus divides into 2 (mitosis) or 4 (meiosis))
- Division of the cytoplasm (cytokinesis) (cytoplasm divides = 2 or 4 new cells)
Describe the cell cycle of a typical mammalian cell
- 24 hours to complete a cell cycle
- 90% is interphase
What causes cancer
- result of damage to the genes that regulate mitosis and cell cycle
- leads to: uncontrolled growth + division of cells
- which then leads to: a group of abnormal cells (tumour) which develops and constantly expand
Where do tumours develop
- everywhere in the body
most commonly: - lungs
- prostate gland (male)
- breast and ovary (female)
- L intestine
- stomach
- oesophagus
- pancreas
When does a tumour become cancerous
When it change from: benign —> malignant
What can effect the rate of mitosis
- environment of cell
- growth factors
- 2 types of gene
How do mutant cells form
they form from a mutation to one of the genes that controls the rate of mitosis (as a result of uncontrolled mitosis)
What is a mutant cell
- structurally and functionally different from normal cells
- most die
- those that survive can divide to form clones of themselves, forming tumours
Describe malignant and benign tumours
MALIGNANT
- grow rapidly, less compact, more life-threatening
BENIGN
- grow slowly, more compact, less life-threatening
How is cancer treated
- involves killing dividing cells by blocking a part of the cell cycle
- in this way the cell cycle is disrupted and cell division, and hence cancer growth ceases
- Chemotherapy is used to disrupt the cell cycle
How does chemotherapy drugs disrupt the cell cycle
- Inhibit enzymes needed for DNA replication so cell cannot enter synthesis phase
- inhibiting the metaphase stage of mitosis by interfering with spindle formation
What is the issue with chemotherapy, but why is it still effective
- problem: disrupts cell cycle of normal cells
- However: drugs are more effective against rapidly diving cells
—> cancer cells have fast rate of division = damaged to a greater degree then normal cells
Why do some patients lose hair when undergoing cancer treatment
those normal body cells, such as hair-producing cells, that divide rapidly are also vulnerable to damage
What are some of the cell cycle targets of cancer treatment
- G1 (cell growth +protein production): chemotherapy prevents synthesis of enzymes needed for DNA replication. If theses aren’t produced, cell is unable to enter the synthesis phase, disrupting cell cycle and forcing the cell to kill itself
- S phase (DNA replication): radiation and some drugs damage DNA. At several points in the cell cycle the DNA in the cell is checked for damage. If severe damage is detected, the cell will kill itself — preventing further tumour growth
How do you work out Mitotic index
Mitotic index = Number of whole cells in the field of view undergoing cells division DIVIDED BY total number of whole cells in the field of view
What is the following specialised cell’s function and adaptations: Root hair cell
Function
- Transport water + minerals to plant from soil
Adaptations
- long, thin, elongated shape = large SA
- Numerous microscopic projections (villi) = large SA
What is the following specialised cell’s function and adaptations: sperm cell
Function
- fertilise egg
Adaptations
- Tail for mobility
- stream lined shape
- lots of mitochondria
- acrosome enzymes for penetration
What is the following specialised cell’s function and adaptations: Red blood cell
Function
- transport oxygen for lungs to body tissue. And CO2 back to lungs
Adaptation
- biconcave shape
- no nucleus
- packed with haemoglobin
What is the following specialised cell’s function and adaptations: Palisade cell
Function
- photosynthesis: light —> chemical energy (glucose)
Adaptations
- contains chloroplasts
- large SA
- located in leaf mesophyll
What is the following specialised cell’s function and adaptations: Muscle cell
Function
- contracts to produce movement
Adaptations
- lots of mitochondria
- elongated shape
What is the following specialised cell’s function and adaptations: neurone (nerve cell)
Function
- transmit electrical signals throughout the body
adaptations
- long axon for signal transmission
- dendrites for signal reception
- myelin sheath for insulation
What is the following specialised cell’s function and adaptations: ciliated cell
Function
Moving mucus and debris in respiratory tract or ova in fallopian tube via ciliary action
Adaptations
- numerous cilia on surface
- constant production of cilia to replace damaged ones
What is the following specialised cell’s function and adaptations: white blood cell
Function
- produces antibodies to fight infections and phagocytosis
Adaptations
- filled of lysosomes for digesting pathogens
- Antigen receptors
- flexible shape
What is the following specialised cell’s function and adaptations: Egg cell
Function
- fertilise with sperm
Adaptations
- large size to store nutrients for growth
- protective outside layer
- limited cytoplasm so only one sperm can fertilised
