B3. Cell Structure (DONE) Flashcards
What is the definition of resolution?
The ability to distinguish two points on an image
What are the differences between electron microscopes and optical microscopes?
Optical: Uses light; Limited resolution due to using light; Max useful magnification 1500x; Cheap; Specimens alive
Electron: Uses electrons; Very high resolution; Useful max magnification 1.5 million x; Expensive; Specimens dead
What are the two type of electron microscopes?
Transmission electron microscopes TEMs; Scanning electron microscopes SEMs
How do TEMs work?
Uses electromagnets to focus beam of electrons; Beam transmitted through specimen
What are the advantages and disadvantages of TEMs?
Advantages: High resolution; Allows internal structures to be seen;
Disadvantages: Only works on thin specimens; Cannot observe living specimen due to being in vacuum; Long treatment time to prepare specimen, artefacts can appear; Non coloured image
What are the advantages and disadvantages of SEMs?
Advantages: Can be used on thick or 3D specimens; Allow external 3D structure to be observed;
Disadvantages: Lower resolution than TEMs; Cannot observe live specimens; Non coloured image
How do SEMs work?
Scans a beam of electrons across the specimen; Beam bounces off surface of specimen and electrons are detected; Forms image;
What is the equation for calculating magnification?
Size of image / Actual size of specimen
What is cell fractionation?
Process of separating cell organelles from each other; Three stages, Homogenisation, filtration, ultracentrifugation
What is homogenisation?
Biological term describing the breaking up of cells
What condition solution are tissue samples placed in before homogenisation?
Place tissue in: Cold, reduce activity of enzyme; Isotonic, prevent water moving into cell via osmosis; Buffered, add buffer solution to prevent denaturing of proteins;
What is a homogeniser?
Blender like machine that grinds cells up, breaks plasma membrane releasing organelle into solution (homogenate)
What occurs in filtration of cell fractionation?
Homogenate filtered through gauze; Separates large unbroken debris; Solution of mixed organelles left (filtrate)
What is a centrifuge?
Machine that separates organelle by spinning at high speeds
What occurs in the ultracentrifugation stage of cell fractionation?
Filtrate placed in centrifuge: spun at low speed, heavy organelles settle at bottom of tube (pellet); Supernatant drained and placed in another tube; Centrifuge spun at higher speeds; Organelle settle at bottom (pellet); Repeated till desired organelle extracted
What is supernatant?
The solution the rest of the organelles stay suspended in above the pellet
What are the order of heavy to light organelle?
Nuclei, Chloroplasts, Mitochondria, Lysosomes, Endoplasmic Reticulum, Ribosomes
What does the cells surface membrane do and what does it consist of?
Surrounds all cells; Controls exchange of materials between internal and external environment; Partially permeable; Consists of a phospholipid bilayer
What does the cells wall do and what does it consist of?
Formed outside of cell membrane; Offer structural support to cell; Polysaccharide cellulose in plants, peptidoglycan in bacteria cells
What are the parts of a nucleus?
Nucleolus, chromatins, nucleoplasm, nuclear pores, nuclear envelope,
What does the nucleus do?
Contains genetic material; Contains instructions for protein synthesis; Nuclear envelope, double membrane that surrounds the nucleoplasm and has pores; Nuclear pore channels allow mRNA, ribosomes to leave nucleus and enzymes, signaling molecules to enter; Nucleolus, dark spot, sites of ribosome production
What is a chromatin?
Complex of DNA and histone proteins
What are chromosomes?
Sections of linear DNA tightly wound around histone proteins
What are the parts of mitochondria and what are its functions?
Inner membrane, cristae, matrix, outer membrane; Site of aerobic respiration; Surrounded by double membrane, inner membrane folded to form cristae; Matrix formed by cristae contains enzymes for aerobic respiration, producing ATP; Mitochondrial DNA, ribosomes are found in matrix
What is the structure of Chloroplast?
Surrounded by double membrane; Membrane bound components, thylakoids containing chlorophyll stack to form grana; Grana joined by lamellae; Light-dependant stages in thylakoids; Light-independent stages in stroma; Chloroplast DNA; Starch granules; Ribosomes; Drops of lipids
What is the purpose of chloroplast?
Site of photosynthesis; Light energy used to derive carbohydrate molecules from carbon dioxide
Describe ribosomes and their purpose.
Site of translation; Found freely in cytoplasm of cells or part of RER in eukaryotic cells; Ribosomes are a complex of ribosomal RNA and proteins; Eukaryotic cells - 80s; Prokaryotes, mitochondria and chloroplasts - 70s
Describe the structure of the endoplasmic reticulum?
Consists of flattened membrane-bound sacs; Rough endoplasmic reticulum; Smooth endoplasmic reticulum
Describe the structure and purpose of the rough endoplasmic reticulum.
Surface covered in ribosomes; Formed from continuous folds of membrane, continues from nuclear envelope; Process proteins made by ribosomes
Describe the structure and purpose of smooth endoplasmic reticulum.
No ribosomes on surface; Involved in production, processing and storage of lipids, carbohydrates and steroids
Describe the structure and purpose of the golgi apparatus.
Flattened sacs of membranes; Modifies protein and lipids before packaging them into golgi vesicles; Vesicles transport protein and lipids to destination
Describe structure of the large permanent vacuole.
Sac in plant cells surrounded by tonoplast; Selectively permeable membrane; Vacuoles in animal cells are not permanent and are small
Describe purpose and structure of vesicles.
Membrane bound sac for transport and storage;
Describe the structure and purpose of lysosomes.
Specialist vesicles; Contains hydrolytic enzymes (break biological molecules down); Breaks down waste material; Used by immune system cells and in apoptosis (programmed cell death)
Describe the structure of centrioles.
Hollow fibres made of microtubules; 2 centrioles at right angle to each other, form centrosomes; Organise and form spindle fibres in cell division; Not in flowering plants and fungi
Describe the structure of microtubules.
Cytoskeleton of cell, provide support and movement; Made of α and β tubulin combine forming dimers; Dimers join into protofilaments; 13 protofilaments in cylinder makes a microtubule
Describe the purpose of microtubules.
Cell membrane projections, increase surface area for absorption
Describe the purpose of cilia.
Hair-like projections made from microtubules; Allows movement of substances over cells
Describe the purpose of flagella.
Made from longer microtubules; Contract to provide cell movement
What is a tissue?
Collection of cells that perform a specific function
What is an organ?
Combination of tissues that are coordinated to perform a variety of functions
Which organelles are always in prokaryotes and which organelle are sometimes in prokaryotic cells?
Always: Cell wall (murein) , cell surface membrane, cytoplasm, circular DNA, ribosomes;
Sometimes: Flagella, capsule, plasmid, pili
How are prokaryotic cells different to eukaryotic cells?
Smaller; Cytoplasm lacks membrane bound organelle; Ribosomes 70s; No nucleus, circular DNA instead; Cell wall made of murein; Binary fission
Describe the structure of viruses.
Acellular non-living infectious particles; Smaller than prokaryotes; Nucleic acid core; Capsid, protein coat; Membrane phospholipid envelope; Parasitic
What is mitosis?
Cell division forming 2 genetically identical daughter cells
What are the phases of mitosis?
Prophase, metaphase, anaphase, telophase
What occurs in interphase?
Cell increases in mass & size; 3 phases G1 - cell makes RNA , enzymes and other proteins needed for growth, S - nucleus DNA replicates, G2 - cell continues to grow and DNA is checked;
What are the phases of the cell cycle?
Interphase, nuclear division, cytokinesis
What occurs in prophase?
Chromosomes condense (visible when stained); Sister chromatids join at centromere; 2 centrosomes move to opposite poles; Spindle fibres begin to emerge from centrosomes; Nuclear envelope breaks down into small vesicles
What are sister chromatids?
2 identical chromatids that make up chromosomes
What occurs in metaphase?
Centrosomes reach opposite poles; Spindle fibres continue to extend from centrosomes; Chromosomes line up at equator of spindle; Spindle fibres attach to centromeres of chromosomes; Each sister chromatid is attached to spindle fibre from opposite poles
What occurs in anaphase?
Sister chromatids separate at centromere; Spindle fibres shorten; Separated sister chromatids (now chromosomes) are pulled to opposite poles
What occurs in telophase?
Chromosomes arrive at opposite poles, begin to decondense; Nuclear envelope forms around each set of chromosomes; Spindle fibres break down
What occurs in binary fission?
Circular DNA molecule undergoes replication; Plasmids undergo replication; Parent cell divides into 2 cells w/ cytoplasm halved; Daughter cells have 1 copy of circular DNA and a variable number of plasmids
