3.2.1 Cell structure Flashcards
Define magnification
how many times larger the image is compared to the object
Define resolution
minimum distance between two points on the sample in which they can still be viewed as separate
What is the formula for magnification ?
magnification = image size / object size
How can you calculate magnification of cell ?
measured length of scale / given length of scale
- must be in the same units
How can you convert between mm, micrometres and nm ?
Big to small = multiply by 1000
Small to big = divide by 100
What is an eyepiece graticule ?
a glass disc on the eyepiece with an etched on scale
-this can be used to measure the size of objects under the microscope
-Must be calibrated for each objective lens
- No fixed units
What is the stage micrometer ?
glass disc on the microscope slide which has fixed units and is used to callibrate the eyepiece graticule
- Divided into 100 equal units of 10 micrometres (Fixed units)
How can the stage micrometer be used to callibrate the eyepiece graticule ?
- Line up the stage micrometer and graticule
- Count the** number of divisions **on the graticule which fit into one micrometer division
- Find the **ratio **(eg 20 graticule divisions fit into 10 micrometer divisions) - 2:1 ratio
- Calculate the** size of one division** on the graticule at the current magnification
(micrometer division / graticule divisions) - Measure the object size ( Divisions x size of one division)
How does a light microscope work?
a beam of light is condensed to form an image
Give the advantages and limitations of a light (optical microscope)
Advantages:
- Colour images
- living samples
- simple preparation (less change of artefacts)
Limitations:
- Maximum resolution of 0.2 micrometres (cannot see ribosomes or lysosomes)
- Maximum magnification of x1500
Poorer resolution as light has a longer wavelength
How does a transmission electron microscope work?
electrons are fired from an electron gun and pass through a thin section of the specimen
- Electron beam is focused using an electromagnet
- Denser parts absorb more electrons so appear more dark
- Image produced is 2D and shows the internal cell structure
Give the advantages and limitations of a transmission electron microscope
Advantages:
- Higher resolution and magnification than light microscope
- Shows internal structure
Limitations:
- Thin samples needed
- In a vacuum so specimens must be dead
- Complex staining process could cause artefacts
- Black and white
- 2D image
How does a scanning electron microscope work?
Beam of electrons focused onto the** specimen surface,** these are scattered and detected to form an image
- Image is 3D and shows the cell surface
Give the advantages and limitations of a scanning electron microscope
Advantages:
-Can use thicker specimens
-Shows a 3D structure
Limitations:
-Lower resolution than TEM
-Does not show internal structures
-Black and white image
-Dead specimen
Define cell fractionation
cell is broken up so that organelles are released for separation, so structure and function can be studied
What are the three aspects the solution must have before fractionation ?
- Cold - reduces enzyme activity so they do not digest the released organelles
- Isotonic - same water potential, prevents osmosis which prevents organelles shrinking or bursting due to osmotic pressues
- Buffered - maintains a constant pH to stop enzymes/proteins denaturing
What is the first stage of cell fractionation ?
Homogenisation
- Cells are broken open in a blender (in the prepared solution)
- Breaks the plasma membrane and releases organelles
What is the second stage of cell fractionation ?
Filtration
- Solution is filtered to remove large debris, leaving a homogenate
What is the third stage of cell fractionisation ?
Ultracentrifugation (organelles separate based on density)
* Spun in a centrifuge at a high speed
* Heavy organelles form a thick sediment at the bottom (pellet)
* Supernatent forms
* Differential centrifugation - process is repeated at increasing speeds, removing the supernatent each time until all the organelles are separated out
Give the order of organelles based on density
Least dense (last to separate)
* ribosomes
* endoplasmic reticulum
* lysomes
* mitochondria
* nuclei
Most dense (first to separate)
What is an artefact ?
dust, air bubbles which occur during preparation and can impact the image seen
- To overcome this scientists need to prepare specimens in a different way
Define eukaryotic cell
a complex cell with a membrane bound nucleus and chromosomes
Eg. animal, plant, fungi
Give the structure of the cell surface membrane
- surrounds the cell
- formed from a phospholipid bi-layer
- partially permeable
Give the function of the cell surface membrane
- regulates movement of substances in and out of the cell
- has receptor molecules which allow it to respond to chemicals (hormones)
Give the structure and function of the nucleus
Function - holds the cells genetic material
* * Nucleolus - site of RNA and ribosome production, site of DNA replication and transcription
* Nuclear pore - allows** MRNA and ribosomes to exit** and allow enzymes to travel in
* Nuclear envelope - double membrane with many pores
* Contains chromosomes (make of chromatin), sections of linear DNA tightly wound around proteins called histones
Visible with a light microscope
Give the structure and function of mitochondria
Function - site of aerobic respiration and ATP production
* Cristae (folded inner membrane) - large surface area for attachment of enzymes and other proteins
* Matrix (fluid centre) - contains enzymes needed for aerobic respiration (ATP)
* Circular mitochondrial DNA - needed for replication
Just visible with a light microscope
Give the structure and function of the chloroplasts
Function - site of photosynthesis
* Grana - stacks of thylakoids which contain chlorophyll (light dependent stage occurs)
* Lamellae - link the grana
* Stroma (fluid filled matrix) - contains enzymes for the **synthesis of sugars **which occurs here (Light independent stage)
visible with a light microscope
Give the structure and function of the golgi apparatus and golgi vesicles
Main function - processes and packages new lipids and proteins
* folded and flattered sacs of memrane
* produces secretory enzymes
* secretes carbohydrates
* transports and stores lipids
* forms lysosomes
VESICLES - STORE the lipids and proteins before transporting them out of the cell (they are brought to the cell surface and fuse with the memrane before release)
visible with a light microscope
Give the structure and function of the lysosomes
Function - break down pathogens and waste materials
* produced by the golgi apparatus (separated from the cell by a membrane
* contain digestive enzymes (lysozymes - hydrolytic enzymes)
* Lysozymes digest….
- pathogens
- worn out organelles (for reuse of materials)
- the cell after it dies
Not visible with a light microscope
Give the structure and function of ribosomes
Function -** site of protein synthesis**
* float freely in the** cytoplasm **or are attached to the rough endoplasmic reticulum
* Make of rRNA and proteins
* Small and large subunits
* Two types
- 80s = eukaryotic cells
- 70s = prokaryotic cells
Give the structure and function of the rough endoplasmic reticulum
Function -** folds and processes proteins**
* folded fluid-filled membranes called cisternae
* surface is covered in ribosomes - so protein synthesis occurs here
Give the structure and function of the smooth endoplasmic reticulum
Function - **synthesises and stores lipids (phospholipids and cholesterol) and carbohydrates **
* No ribosomes
Give the structure and function of the cell wall (in plants)
Function - structural support
* outside of the cell membrane
* made of cellulose microfibrils, plasmodesmata connect cytoplasm to neighbouring cells
* Support..
- mechanical strength to prevent the cell bursting under osmotic pressure (turgidity regulates the amount and rate at which water can enter)
- **gives rigidity **to the plant as a whole
Give the structure and function of the permanent vacuole
surrounded by the tonoplast which is a selectively permeable membrane
* makes cells turgid (which prevents wilting)
* temporary store of sugars and amino acids
* pigments can attract pollinators
Define cell diferentiation
process by which a cell becomes specialised to carry out a specific function
Define cell
Give some examples
a membrane bound structure containing biomolecules such as nucleic acids, proteins and polysaccharides
sperm, goblet, neurone, muscle
Define tissue
Give some examples
a group of SIMILAR specialised cells working together to perform a SPECIFIC function
epithelium, xylem, capilliary, nerves, elastic fibres, aorta, palispide mesophyll
Define organ
Give some examples
a combination of DIFFERENT tissues working together to carry out a VARIETY of functions
-Different organs form an ORGAN SYSTEM
lungs, heart, artery, stomach, vein, brain, trachea, bronchiole, kidney, spinal chord
Why are arteries and veins organs while capilliaries are tissues ?
capillaries are only made of epithelium whereas arteries and veins are made of epithelial AND muscle tissue so are organs
Give the levels of organisation in the digestive system
- Organs - Stomach, intestines, liver, pancreas
- Stomach - Made of epithelial , muscular and glandular tissues etc
- Epithelial tissue - made of epithelial cells
Define prokaryotic cells
much smaller than eukaryotic cells and have…
* no nucleus
* no membrane-bound organelles
How do prokaryotic cells differ from eukaryotic cells ?
- smaller
- no nucleus
- no membrane-bound organelles
- smaller ribosomes (70s)
- cell wall made of murein
MAY also contain (often in bacteria) - plasmids
- slime capsule
- flagella
Give the structure and function of plasmids
Structure - small loops of DNA
Function - contain genetic material and can be passed between prokaryotes, genes are often ones which may aid survival (eg antibiotic resistance)
Give the structure and function of the slime capsule
Structure - extra layer on the cell wall
Function:
* protects bacteria from attack (groups of bacteria can stick together which covers the antigens)
* stops cell drying out
Give the structure and function of the flagellum
Structure - long tail
Function - rotates to enable cell movement
Give the structure and function of the cell wall (prokaryotic)
Structure - made of murein
Function - supports cell and stops it bursting under osmotic pressure
Give the function of pili
allow the bacterial cell to attach to specific surfaces on other cells
What are the three main factors which define viruses ?
- Acellular and non-living
- Smaller than bacteria
- Invade and reproduce inside living cells
They are essentially just nucleic acids surrounded by protein
Function of the nucleic acid core in viruses
asexual reproduction
(genomes are either DNA or RNA and can be single or double stranded)
Function of the capsid in viruses
protein coat which contains two single strands of DNA and some enzymes
Function of the attachment protein in viruses
allow the virus to identify and attach to host cells
* they bind to the complementary receptor proteins, which are specific so viruses can only infect one type of cell
