Cell Structure Flashcards
Eukaryotic cell features
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Cell membrane structure and function (eukaryotic)
Made up of a phospholipid bilayer.
• Each phospholipid has a hydrophilic head and a hydrophobic tail.
• Has intrinsic proteins that span the bilayer and extrinsic proteins that are partially embedded in the bilayer.
• isolates cytoplasm from extracellular matter
• Controls the movement of substances into and out of the cell. (Selective permeable)
• involved in cell signalling/recognition
Cell wall structure and function (eukaryotic plants)
- Contain a lot of polysaccharides such as cellulose
- Middle lamella: marks the boundary between adjacent cell walls and cements adjacent cells together
- Provide mechanical strength to the cell
- Allow water to pass along it
Centriole structure and function (eukaryotic)
• Small hollow cylinders made of microtubules.
• Create spindle fibres and found in the cytoplasm.
• Found in animal cells but only some plant cells.
Cellulose function (eukaryotic)
Component of cell walls in plants
Chitin function (eukaryotic)
Component of cell walls in fungi
Chloroplast structure and function (eukaryotic plants)
Where photosynthesis occurs.
*Chloroplast envelope: double plasma membrane. Allows substances to enter and leave the chloroplast
* The grana: stacks of thylakoids in which chlorophyll is contained. The grana are where the first stage of photosynthesis takes place
* Stroma: fluid filled matrix where the second stage of photosynthesis takes place.
Golgi apparatus structure and function (eukaryotic)
Made up of a stack of membranes that make up flattened stacks (cisternae), with small rounded hollow structures called vesicles.
• A factory part of a cell that takes proteins from RER and free ribosomes, and lipids (from SER) to process/modify and package them.
• Processed molecules bud off in vesicles.
• These are either used in the cell or leave by exocytosis.
Lysosome structure and function (eukaryotic)
• A round organelle surrounded by a membrane with no clear internal structure.
• Contains digestive enzymes.
Mitochondria structure and function (eukaryotic)
• Double membrane- inner one is folded to form a structure called cristae,
• Cristae increases the surface area for attachment of enzymes and proteins involved in respiration.
• Inside is the matrix which contains enzymes involved in respiration.
• Produces ATP during aerobic respiration.
Nucleus structure and function (eukaryotic)
• Large organelle surrounded by a nuclear envelope which contains pores.
• The pores allows the movement of mRNA.
• Nucleoplasm containing chromatin (which is made from DNA and proteins)
Nucleolus - dense, made of RNA - makes ribosomes.
• Contains DNA
• Controls cellular processes
Ribosome structure and function (eukaryotic)
• A very small organelle that either floats free in the cytoplasm or is attached to the rough endoplasmic reticulum.
• It is made up of proteins and RNA. No membrane
Rough endoplasmic reticulum structure and function (eukaryotic)
• A system of membrane bound flattened sacs, the surface is covered with ribosomes.
• Proteins enter the RER and are folded and processed
• Then they are transported to the Golgi apparatus in vesicles.
Smooth endoplasmic reticulum structure and function (eukaryotic)
Tubular structure with spaces, it has no ribosomes on its surface.
• Involved in the synthesis, storage and transport of lipids and carbohydrates.
Vacuole structure and function (eukaryotic plants)
- A vacuole is a fluid filled sac bounded by a single membrane (tonoplast)
- It contains mineral salts, sugars, amino acids, wastes and sometimes pigments.
It makes cells turgid - Sugars and amino acids can act a temporary food store
- Pigments may colour petals, attracting insects for pollination.
Prokaryotic cell features
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What is the structure and function of a capsule? (Prokaryotic)
• Prevents desiccation, protects cell from antibiotics and viruses
• Used to adhere (stick) to surfaces.
What is the structure and function of a cell membrane? (Prokaryotic)
• Made of lipid and protein
• Selectively permeable
• Site of most cellular activities in bacteria
What is the structure and function of a cell wall? (Prokaryotic)
• Gives the cell its shape
• Made from peptidoglycan (or murein)
• Different structures help to classify bacteria
What is the DNA loop? (Prokaryotic)
In a single loop not associated with proteins (no chromosomes)
What is the structure and function of a flagellum? (Prokaryotic)
• Used for locomotion
What is the structure and function of the plasmid? (Prokaryotic)
In a single loop not associated with proteins (no chromosomes)
What is the structure and function of ribosomes? (Prokaryotic)
Smaller than eukaryotic ones (70s not 80s)
What is the structure and function of pilli? (Prokaryotic)
Helps attach to host cells
Define the term eukaryotic
DNA is contained in a nucleus, contains membrane - bound specialised organelles
Define the term prokaryotic
DNA is ‘free’ in cytoplasm, no organelles
E.g. bacteria
Specialised cells
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State the relationship between a system and specialised cells
Specialised cells —> tissues that preform specific functions —> organs made up of several tissue types —> organ system
What is cell specialisation?
It’s a process where cells develop specific functions and structures to carry out specific tasks within an organism
Why do specialised cells have fewer/less of certain organelles?
So they can preform their function efficiently
How do the cells become specialised?
Every cell contains all the genes it needs for it to develop into any type of cell, these genes are switched on or off to specialise it
What are examples of specialised cells?
Nerve cell
Muscles cell (Myocytes)
Sperm cell
Ciliated epithelial cell
Xylem vessels
Phloem Vessels
What is the function of the Nerve Cell (Neuron)?
It transmits nerve impulses (electrical impulses) to effected organs (muscles or glands)
What are the features of the nerve cell (neuron)?
Dendrites- projections of a neuron (nerve cell) that receives signals (information) from other neurons. They form connections between neurons
Myelin sheath - (fatty coating) for increase connection speeds and protecting the axon
Axon - to send signals to other nerves, muscle cells or glands
Nodes of Ranvier - gap in the myelin sheath between adjacent Schwann cell (cells that produce myelin sheath around neuronal axons) Allows ions to diffuse in and out of the neuron propagating the electrical signal down the axons
What is the function of muscle cells (myocytes)?
The contract to cause movement
There are 3 types; cardiac, skeletal and smooth. Different because of their abilities to contract and relax when joined as a tissue.
What are the features of muscle cells (myocytes)?
Smooth muscle - unstriated, involuntary muscle fibres (found in the digestive canal)
Skeletal muscle - striated voluntary muscle fibres (attach to bones to create movement by a pulling force when they contract).
Cardiac - striated involuntary muscle fibres. Allow the heart to beat in a rhythmic way. Not consciously controlled.
What is striated muscle tissue?
It features repeating functional units called sarcomeres. The presence of sarcomeres manifests as a series of bands visible which is seen in microscopic images.
What is the function of a sperm cell?
To carry DNA from the father to the egg and allow fertilisation.
What are the features of a sperm cell?
Acrosome (pointed head) containing enzymes which break down the wall of the egg for fertilisation.
Middle piece has many mitochondria whichrelease energy for movement.
Tail (flagellum) for movement.
Nucleus has DNA from father.
What is the function of a ciliated epithelial cell?
They line the surface of organs and have protective/secretory function
What are the features of a ciliated epithelial cell?
Consist of sheets of cells
Flat cells that line the surface of organs where diffusion takes place – e.g. Alveloli in lungs.
Ciliated epithelium in Trachea- Cilia are used to move mucus over the surface of the epithelium.
What is the function of xylem vessels?
Transports water and minerals in plants.
What are the features of the xylem vessels?
Xylem vessels consists of dead hollow cells because the walls are lignified and the contents disintegrate. The lignin helps to make the cell wall impermeable so they are in effect waterproof and strengthens the vessel.
Allows water to move unidirectionally – up from roots to different parts of the plants.
Provides mechanical support.
What is the function of phloem vessels?
Transports sugars made in photosynthesis (the source) to sinks – where they are stored or used by the plant for growth.
What are the features of the phloem vessels?
Consists of Sieve tubes - Specialised for transport and have no nuclei. Each sieve tube has a perforated end, a sieve plate, so its cytoplasm connects one cell to the next.
Companion cells - Have mitochondria that release energy for transport. A sieve tube is completely dependent on its companion cell(s).
Viruses and bacteria
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What is the structure of bacteria?
A DNA loop, enzymes, plasmids, ribosomes which are contained in the cytoplasm
Then a cell membrane followed by cell wall then a capsule which is sticky
Pili are attached to the capsule which help the bacteria attach to the host cell
A flagellum to allow the bacteria to move
What do bacteria have in their cell walls?
Peptidoglycan (Murein) in its cell walls
What size are bacteria cells?
1-10um
What is bacteria replication called?
Binary fission
What type of replication is binary fission?
Asexual
Are there spindle fibres in binary fission?
No
Does binary fission produce identical cells?
No as they can have different numbers of plasmid copies
What is the first step of binary fission?
DNA and plasmids replicate. Plasmids can be replicated many times
What is the second step of binary fission?
Cell elongates and DNA moves to opposite poles of cell
What is the third step of binary fission?
Cytoplasm begins to divide and new cell wall begins to form
What is the fourth step of binary fission?
The cytoplasm divides to produce two daughter cells. nEach contain an identical DNA loop but can contain different numbers of plasmid copies
What are the features of viruses?
They are neither prokaryotic nor eukaryotic
They are acellular non-living particles - can’t multiply without invading a host cell
How big are viruses?
10-100nm
They are 1000x smaller than bacteria
What is the structure of viruses?
They consist of -
Genetic material (RNA) that is protected by a protein coat called the capsid
They may be enclosed in a lipid envelope
The capsid or lipid envelope will have attachment proteins/antigen to help them recognise a host
The matrix and reverse transcriptase (in some)
How to viruses replicate?
With the aid of living cells
What is step one of virus replication?
Virus detects host cell by recognising protein marker on its membrane. The virus attaches to cell using attachment proteins
What is step two of virus replication?
Virus injects genetic material into the cell
What is step three of virus replication?
Cell reproduces the genetic material and reads it creating new viral proteins
What is step four of virus replication?
Virus leaves callousing some of their cells own membrane to form itself
Ultracentrifugation
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What is cell fractionation?
It is a process where cells are broken up and the different organelles they contain are separated out based on their size/mass using gravity
What are the three stages in cell fractionation?
homogenisation, filtration, ultracentrifugation
Why is having the cell in a cold, isotonic, buffered solution important?
Cold - reduces enzyme activity which may break down organelles
Isotonic - (same water potential as original tissue) to prevent organelles from bursting/shrinking due to osmotic gain/loss of water
Buffered - to maintain a constant pH
What is the first step in ultracentrifugation?
Homogenising (blending) breaks up the tissue to break open cell membranes and release the organelles
What is the second step in ultracentrifugation?
The homogenate is filtered to remove large debris as these will be heavy and sing to the bottom of the test tube
What is the third step in ultracentrifugation?
Centrifuging - Faster the spinning the greater the force. At slower speeds the larger fragments collect at the bottom of the tube forming a pellet and smaller ones remain near the top stay suspended in a liquid called the supernatant. Each time the supernatant remaining is re-spun at a higher speed and some of the smaller organelles collect at the bottom forming a new pellet. The method is repeated to collect smaller organelles will be recovered.
What is the order of organelle fractionation (with speed) ?
x1000 - nuclei - (after 10 mins)
x3500 - chloroplasts - (after 10 mins)
x3500 - mitochondria - (after 10 mins)
x16500 - lysosomes - (after 20 mins)
x16500 - endoplasmic reticulum - (after 20 mins)
x100000 - ribosomes - (after 60mins)
