3.2.1 Cell structure Flashcards
Define Eukaryotic
DNA is contained in a nucleus and contains membrane bound specialised organelles
Where are Eukaryotic cells found?
- Plants
- Animal
- Fungi
- Protists
Details about the Cell surface membrane
‘Fluid mosaic’ phospholipid bilayer in which intrinsic and extrinsic proteins are embedded
- Involved in cell signalling and cell recognition
- Selectively permeable to regulate transport of substances
Details about the Endoplasmic reticulum
Flattened membrane bound sacs (cisternae) which are continuous with the outer nuclear membrane
- Rough has ribosomes
- Smooth no ribosomes
- Smooth ER synthesis , stores and transports lipids and carbs
- Rough ER transports proteins made on attached ribosomes
Details about the Cell wall (plants/algae/fungi)
Made of cellulose microfibrils , plasmodeta allows molecules to pass between cells , middle lamella acts as boundary between adjacent cell walls
- Mechanical strength and support
- Physical barrier against pathogens
- Part of the apoplast pathway for the easy diffusion of water
Details about the Cell vacoule (plants)
Surrounded by single membrane called the tonoplast which contains cell sap
- Controls turgor pressure
- Absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm
Details about the Mitochondria
Surrounded by a double membrane serrated by a fluid filled space called the matrix which contains lipids , proteins , respiratory enzymes and mitochondrial DNA. Inner membrane is folded to form Cristae which gives a large surface area and is the site of electron transport chain
- Site of aerobic respiration to produce ATP
Details about the Golgi apparatus
Consists of a stack of membranes that make up flattened sacs with vesicles
- Forms lysosomes , synthesis glycoproteins and modifies and packages proteins for export
Details about Lysosome
Type of golgi vesicle that releases lysozymes and is a sac surrounded by a single membrane. The glycoprotein coat protects cell interior and embedded H+ pump maintains acidic conditions
- Exocytosis of digestive enzymes and digests contents of phagosome
Details about Ribosomes
Formed of protein and rRNA and free in cytoplasm or attached to endoplasmic reticulum
- In eukaryotic cells: 80s
- Site of protein synthesis via translation
- Large subunit joins amino acids
- Small subunit contains mRNA binding site
Details about Chloroplast (plants/algae)
Vesicular plastid with double membrane , thylakoids are flattened discs stacked to form the grand which contains photosystems with chlorophyll and fluid-filled matrix called the stroma
- Site of photosynthesis
- Converts solar energy to chemical energy
Details about the Nucleas
Contains chromosomes consisting of protien bound linear DNA and is a sac surround by a nuclear envelope (double membrane) , nuclear pores allow substances to enter and exit
- Manufactures ribosomal RNA and ribosomes
- Contains DNA coiled around chromatin into chromosomes
- Controls cellular processes
Define Prokaryotic
DNA is free in cytoplasm and no organelles e.g. Bactria/archaea
What are Plasmids?
Small rings of DNA that carry non essential genes
What is a Flagella?
Rotating tail which propels organism
What is a Capsule and what is its role?
Polysaccharide layer
- Prevents desiccation
- Acts as a food reserve
- Provides mechanical protection against phagocytosis and external chemicals
- Sticks cells together
What do Eukaryotic and Prokaryotic cells have in common?
- Cell membrane
- Ribosomes
- Cytoplasm
Contrast Eukaryotic and Prokaryotic cells
Prokaryotic
- unicellular and small
- no membrane bound organelles and no nucleus
- circular DNA not associated with proteins
- small ribosomes = 70s
- murein cells walls
- contains capsule and sometimes plasmids
Eukaryotic
- often multicellular and large
- always have organelles and nucleus
- linear chromosomes associated with histone proteins
- larger ribosomes = 80s
- cellulose cell wall
- no capsule and no plasmids
What are Viruses?
- Acellular and non living
- No cytoplasm
- Can’t self reproduce
- No metabolism
Structure of a Viral particle
- No cytoplasm
- Surrounded by capsid which is a protein coat made of capsomeres
- Linear genetic material and viral enzymes
Structure of an Enveloped virus
- Simple virus surround by matrix protein
- Matrix protein surrounded by envelope
- Attachment proteins on surface
Role of the Capsid on viral particles
- Protects nucleic acid from degradation
- Surface sites enable viral particle to bind to and enter host cell or inject their genetic material
Role of attachment proteins on viral particles
Enable viral particle to bind to complementary site on host cell
Formula for Microscopy
I
A M actual size = image size/magnification
State the order of sedimentation of organelles during differential centrifugation
Most dense to least dense
- nucleus
- mitochondria
- lysosomes
- rer
- plasma membrane
- ser
- ribosomes
Define Magnification
Factor by which the image is larger than the actual specimen
Define Resolution
Smallest seperation distance from which 2 separate structures can be distinguished from one another
Outline what happens during cell fractionation and ultracentrifugation
- Mince and homegneize tissue to break open cells and release organelles
- Filter homogenate to remove debris
- Perform differential centrifugation
- Spin homogenate in centrifuge
- The most dense organelles in the mixture form a pellet
- Filter off the supertant and spin again at a higher speed
Explain why fractionated cells are kept in a cold , buffered and isotonic solution
Cold: slow action of hydrolyse enzymes
Buffered: maintains constant PH
Isotonic: Prevents shrinking of organelles
Explain how the length of a cell could be estimated
Measure using a graticule and calibrate against a scale of known lengths
Describe how a Scanning electron microscope (SEM) works
- Focus a beam of electrons onto specimens surface using electromagnetic lenses
- Reflected electrons hit a collective device and are amplified to produce an image on a photographic plate
Advantages of using SEM
- 3D image
- Electrons have a shorter wavelength than light so a high resolution
Disadvantages of using SEM
- Only shows outer surface
- No colour image
- Requires a vacuum so can’t show living structures
Describe how a Optical microscope works
- Lenses focus rays of light and magnify the view of a thin slice of specimen
- Different structures absorb different amounts and wavelengths of light
- Reflected light is transmitted to the observer via the objective lens and eyepiece
Advantages of using Optical
- Colour image
- Shows living structures
- Affordable apparatus
Disadvantages of using Optical
- 2D image
- Lower resolution than electron microscopes so can’t see ultrastructures
Describe how a Transmission electron microscope (TEM) works
- Pass a high energy beam of electrons through thin slice of specimen
- More dense structures appear darker since they absorb more electrons
- Focus image onto fluorescent screen or photographic plate using magnetic lenses
Advantages of using TEM
- High magnification as electrons have a shorter wavelength than light so a high resolution so ultrastructure is visible
Disadvantages of using TEM
- 2D image
- No colour image
- Requires a vacuum
- Extensive preparation needed
