Cell Structure Flashcards
What is a eukaryotic cell?
- DNA is contained in a nucleus
- contains membrane-bound specialised organelles
What is a prokaryotic cell?
- DNA is ‘free’ in cytoplasm
- no membrane-bound organelles
What is the structure of the nucleus in eukaryotic cells?
- surrounded by a nuclear envelope (semi-permeable double membrane)
- nuclear pores (allow substances to enter/exit)
- dense nucleolus made of RNA and proteins (assembles ribosomes)
What are 2 functions of the nucleus?
- contains DNA coiled around chromatin into chromosomes
- controls cellular processes (gene expression determines specialisation and site of mRNA transcription, mitosis, semi-conservative replication)
What is the structure of the mitochondria?
- surrounded by double membrane
- folded inner membrane forms cristae (site of electron transport chain)
- fluid matrix (contains mitochondrial DNA, respiratory enzymes, lipids and proteins)
What is the structure of the chloroplast?
- vesicular plastid with double membrane
- thylakoids (flattened disks that stack up to form grana)
- intergranal lamellae (tubes that attach thylakoids in adjacent grana)
- stroma (fluid-filled matrix)
What is the function of mitochondria?
Site of aerobic respiration to produce ATP
What is the function of chloroplasts?
Site of photosynthesis to convert solar energy to chemical energy
What are 2 functions of the Golgi apparatus?
- modifies and packages proteins for export
- synthesises glycoproteins
What are 2 functions of lysosomes?
- digests contents of phagosome
- exocytosis of digestive enzymes
What is the function of ribosomes?
Site of protein synthesis via translation (large subunit joins amino acids, small subunit contains mRNA binding site
What are attached onto RER?
Ribosomes
What is the function of RER?
Ribosomes attached for protein synthesis and transport
What is the function of SER?
Lipid synthesis
What is the cell wall in bacteria made from?
Murein
What is the cell wall in plants made from?
Cellulose which contains lots of microfibrils
What are 2 functions of the cell wall?
- provides strength and support
- physical barrier against pathogens
What are 2 functions of the permanent vacuole?
- controls turgor pressure
- absorbs and hydrolyses potentially harmful substances to detoxify cytoplasm
Give 3 common cell adaptations
- folded membrane or microvilli (increase surface area for diffusion)
- many mitochondria (large amounts of ATP for active transport)
- walls are one cell thick (reduce distance of diffusion pathway)
What is the role of plasmids in prokaryotes?
Small ring of DNA that carries non-essential genes
What is the role of flagella in prokaryotes?
Rotates to push the cell through its environment
What is the role of the capsule in prokaryotic cells?
Protects the cell from attack by antibiotics or white blood cells
What is the role of pili on prokaryotic cells?
Attaches prokaryotic cells to other cells or surfaces
Which microorganisms are considered acellular?
Viruses
What does acellular mean?
Not made up of cells
Give 2 things that are always present in a virus
- genetic material
- capsid
Give 3 things that are sometimes present in viruses
- envelope
- glycoproteins
- enzymes
What is the first stage in viral replication?
- the virus uses its attachment proteins to bind to specific receptor proteins on host cells
What is the second stage in viral replication?
The virus injects its viral DNA or RNA into the host cell
What is the third stage in viral replication?
The virus use the host cell’s machinery and resources, such as enzymes and ribosomes, to replicate viral particles
What is the fourth and final stage in viral replication?
New viral particles are released from the host cell
What is the equation for magnification?
Image size / actual size
What is the ability to distinguish between two separate points?
Resolution
How do you convert cm to mm
Multiply by 10
How do you convert mm to micrometres?
Multiply by 1000
How do you convert micrometres to nm?
Multiply by 1000
Why do electron microscopes have a better resolution than light microscopes?
They have a shorter wavelength
What are the two types of electron microscopes?
- transmission electron microscope
- scanning electron microscope
How do transmission electron microscopes work?
They use electromagnets to transmit a beam of electrons through a specimen. The denser parts absorb more electrons, so appear darker in the image formed
Which type of electron microscope can be used to observe the internal structures of organelles?
Transmission electron microscope
What type of organisms can be observed under a SEM and TEM?
Non-living or dead
Which electron microscope has the better resolution?
Transmission electron microscope
Which electron microscope produces a 3D image?
Scanning electron microscope
What are the four main steps in cell fractionation?
- sample preparation
- homogenisation
- filtration
- ultracentrifugation
What are the 3 characteristics that the solution used in the sample preparation has?
- ice-cold
- isotonic
- buffered
remember ice, ice, baby!
Why does the solution used in sample preparation need to be ice-cold?
Slows down enzyme activity that might otherwise break down organelles
Why does the solution used in sample preparation need to be isotonic?
Ensure that the water potential inside and outside the organelles is the same, preventing damage through water movement
Why does the solution used in sample preparation need to be buffered?
Keeps the pH constant with is crucial to prevent denaturation of proteins and enzymes
What does homogenisation involve?
Physically breaking open the cells
What is the purpose of homogenisation?
Disrupts the plasma membrane, allowing the organelles to be released into the solution
How can you homogenise cells?
Use a blender to grind them up
Why is the mixture filtered after homogenisation?
To remove larger pieces of cell debris and any remaining tissue fragments
What is the filtration usually done by during cell fractionation?
Gauze
Why is the solution filtered through a gauze during cell fractionation?
Allows smaller organelles to pass through while retaining the larger debris
Ultracentrifugation is the process used to separate organelles based on their _________
Density
What is the pellet during ultracentrifugation?
The sediment at the bottom of the tube containing the heavier organelles
What is the supernatant during ultracentrifugation?
Liquid remaining above the pellet which contains the lighter organelles
Describe the process of ultracentrifugation
- Cell fragments are placed in a centrifuge tube and spun at a low speed
- Heaviest organelles form a pellet at the bottom, lighter organelles form the supernatant above
- Supernatant transferred to another tube and centrifuged at a higher speed
- 2 and 3 repeated, increasing the speed each time to separate remaining organelles until all separated into distinct layers
