1.0 Cell Structure Flashcards
Magnification Formula
Magnification = image size (mm->micrometers) / actual size of specimen (micrometers)
Eyepiece graticule and Stage Micrometer
what is resolution
the ability to distinguish between two separate points
What is magnification
how many times bigger an image of a specimen observed is compared to the actual (real-life) size of the specimen
Magnification in light microscope
- has two types of lenses
1. eyepiece lens: usually has a magnification of 10
2. a series of (usually 3) objective lenses, each with a different magnification
3. calculate total magnification : eyepiece lens x objective lens = total magnification
Resolution in Light vs Electron microscope
LIGHT:
- resolution is limited by the wavelength of light
- as light passes through the specimen, it will be diffracted
- the longer the wavelength of light, the more it is diffracted
- diffraction will overlap as the points become closer
ELECTRON:
- higher resolution than light microscopes
- bc electrons have a much smaller wavelength than visible light
- therefore, they can be much closer before the diffracted beams overlap
Electron vs Light microscope
LIGHT:
- used for specimens above 200nm
- light shines through specimen, then light passes through objective lens (changeble) and eyepiece lens (x10), this magnifies the specimen to give an image that can be seen by the naked eye
- specimens can be living or dead
- useful for looking at whole cells, organisms, tissues within organs
ELECTRON
- 2 types: scanning and transmission
- both are used for specimens above 0.5 nm
- a beam of electrons are fired at the specimen, scanning: small beam that moves across the specimen, transmission: broad static beam
- due to the higher frequency of electron waves (shorter), magnification is greater
- specimens must be dead
Cell surface membrane
STRUCTURE:
- phospholipid bilayer : phospholipids and proteins are constantly in motion
- proteins (intrinsic & extrinsic, channel & carrier)
- glycolipids & glycoproteins
- cholesterol
- hydrophillic head, hydrophobic tail
- around 10nm in diameter
FUNCTIONS:
- controls the exchange of materials between the internal cell environment and the external environment
- controls what goes in and out of the cell
- partially/selectively permeable
Cell wall
STRUCTURE:
- polysaccharide cellulose in plants
- peptidoglycan in most bacterial cells
- narrow thread of cytoplasm (surrounded by cell membrane) plasmodesmata connect cytoplasm of neighbouring plant cells
FUNCTION:
- provides structual support for the cell
- is freely permeable unlike cell surface membrane
Nucleus
STRUCTURE:
- contains chromatin (genetic material)
- double membrane bound
- in all eukaryotic cells
- nuclear envelope with pores
- nucleolus (stained darker under microscope)
- largest organelle
FUNCTION:
- genetic material for protein synthesis
- site of transcription of genes and production of mRNA
- pores provide channels for mRNA, ribosomes to travel out, enzymes (DNA polymerase) and signalling molecules to travel in
- nucleolus is the site of ribosome synthesis
Chloroplast
STRUCTURE:
- 2nd largest organelle (larger than mitrochondria)
- double membrane bound (prokaryotic origin)
- membrane-bound compartment : thylakoids (flattened membrane sacs)
- stacks of thylakoids: grana
- chlorophyll is embedded within thylakoid membrane
- granas’ connected by lamellae (thin & flat thylakoid membranes)
- contains 70s ribosomes
- found in palisade mesophyll, spongy mesophyll and surface of stem
FUNCTIONS:
- site of photosynthesis
- light-dependent stage: takes place in thylakoids (synthesizes ATP)
- light-independent stage: takes place in stroma: interior solution (Calvin Cycle)
- ribosomes used to synthesise proteins needed in chloroplast replication (binary fission) and photosynthesis
Ribosome
STRUCTURE:
- consists of ribosomal RNA & proteins (synthesised in nucleus)
- 70s: in prokaryotes, mitochondria and chloroplasts (18nm)
- 80s: in eukaryotes, cytoplasm and RER (25nm)
- smallest organelle
- not membrane bound
FUNCTIONS:
- site of translation (protein synthesis)
- mRNA is transcribed in nucleus, travels into cytoplasm where ribosomes translates and converts into protein
Rough Endoplasmic Reticulum (RER)
STRUCTURE:
- surface covered with 80s ribosomes
- continuous with nuclear envelope
- made of cisternae (flattened membrane sacs)
- shape: flattened sacs
FUNCTION:
- transports proteins made by ribosomes
- sometimes, protein folding, addition of carb chain to protein in lumen (glycosylation)
Smooth Endoplasmic Reticulum
STRUCTURE:
- network of more tubular and smooth-looking membrane-bound structures
- shape: tubular structure
FUNCTION:
- involved in production, processing, transportation and storage of lipids, carbohydrates and steroids (hormones)
- therefore a lot found in muscle cells
Golgi Body
STRUCTURE:
- flattened sacs of membrane
- made of a series of cisternae
- swelling at end of sacs for vesicle formation
- constantly being formed and broken down
FUNCTION:
- modifies proteins and lipids
- glycosylation (addition of carb chain)
- phosphorylation (addition of phosphate group to proteins)
- packages material into secretory vesicles
- produces lysosymes (with hydrolytic enzymes within)
- involved in exocystosis
Permanent Vacoule
STRUCTURE:
- sac like
- sorrounded by the tonoplast (selectively permeable membrane)
- vacoules found in animals are temporary & small
FUNCTION:
- storage of cell sap, ions, salts, enzymes nutrients, water (maintains cells environment, isolates harmful substances)
- maintains tugor pressure, helps keep the plant cell rigid and supports the structure
- helps manage waste products
Lysosome
STRUCTURE:
- special form of vesicle
- contains hydrolytic enzymes (breaks down biological molecules by hydrolysis)
- produced at Gogli body
- shape: spherical small sacs
FUNCTION:
- in WBC: digest bacteria
- breaks down waste material such as damaged/worn-out organelles (NOT DEAD)
- used extensively by immune system and in apoptosis (programmed cell death)
Centriole
STRUCTURE:
- hollow fibres made of microtubules
- two centrioles at right angles to each other form a centrosome
- not found in plants
FUNCTION:
- centrosome, organises spindle fibres during cell division,
Microtubules
STRUCTURE:
- made up of alpha and beta tubulin combined to form dimers
- dimers join together to form protofilaments
- 13 protofilaments in a cylinders make a microtubule
FUNCTION:
- makes up the cytoskeleton
- used to provide support and movement of cell
- helps navigate vesicles in cytoplasm
Cilia
STRUCTURE:
- hair-like projections
- made from microtubules
FUNCTION:
- allows movement of substances over the cell surface
- cilia in the trachea
microvilli
STRUCTURE:
- cell surface membrane projections
- can be found in the intestinal tract lining
FUNCTION:
- increases the surface area for maximum absorption of material
Mitochondria
STRUCTURE:
- double membrane bound (prokaryotic origin)
- 3rd largest organelle
- divides by binary fission
- inner membrane folded to form cristae (different from cisternae)
- matrix formed by cristae within contains enzymes needed for aerobic respiration
- contains 70s ribosomes
- contains circular pieces of DNA
FUNCTION:
- site of aerobic respiration within eukaryotic cells
- site of ATP synthesis
Plant vs Animal cell
ANIMAL ONLY:
- centrioles
- microvilli
PLANT ONLY:
- chloroplast
- cell wall
- large permanent vacoule
ATP
SIGNIFICANCE:
- all organisms require constant supply of energy to maintain their cells
FUNCTION:
- Anabolic reactions: builds larger molecules from smaller ones
- move substances across the cell membrane (active transport) or to move substances within the cell
- animals: muscle contraction (coordinates movement at a whole-organism level), conduction of nerve impulses
- “universal energy currency”
STRUCTURE:
- Adenosine Triphosphate
- is a nucleotide (monomers of DNA & RNA are also nucleotides)
- three phosphate groups, one ribose sugar and one adenine (nitrogenous base)
Prokaryotes (bacterium)
- organisms that lack a nucleus
- simpler structure
- unicellular
- 1-5 micrometers
- peptidoglycan cell walls
- circular DNA
- 70s Ribosomes
- no double membrane organelles
Prokaryote vs Eukaryote
- SIZE: prokaryotes are smaller (0.5-5 μm) eukaryotes (10-100μm)
- DNA: circular, lies free in cytoplasm, naked (prokaryotes) Linear Surrounded by nucleus Associated with histone, forming chromosome (eukaryotes)
- RIBOSOMES: 70s ONLY (prokaryotes)
- ER: prokaryotes lack ER
- ORGANELLES: no membrane bound organelles (prokaryotes) single, double, non-membrane bound organells (eukaryotes)
- CELL WALL: peptidoglycan, polysaccharide with amino acid (prokaryotes) chitin nitrogen containing polysaccharide in fungi, cellulose & lignin in plants (eukaryotes)
- CELL DIVISION: binary fission (prokaryotic) mitosis & cytokenisis (eukaryotic)
- TRANSCRIPTION & TRANSLATION: simultaneously, due to no nucleus (prokaryotic) consecutively (eukaryotic)
Viruses
STRUCTURE:
- 20-300nm
- non-cellular/ non-living
- nucleic acid core (can have DNA or RNA, single or double stranded)
- protein coat (caspid)
- some viruses have an **envelope of membrane-phospholipids **
FUNCTION:
- parasitic, can only reproduce in a host cell
- takes over protein synthesising organelles (ribosomes) of host cell, helps to produce viral proteins to make caspids
