cell ultrastructure
Cards (31)
- prokaryotic cells lack a distinct nucleus and include the group of organisms called bacteria. their dna takes their form in a single loop and their ribosomes are much smaller than in eukaryotic cells
- eukaryotic cells have membrane bound organelles whereas prokaryotic dont.
- prokaryotic features-no nucleus- dna found in a region called a nucleoid-only one membrane- cell surface or plasma-no membrane bound organelles-cell wall is made of peptidoglycan
- prokaryotic features-smaller ribosomes than eukaryotes (18nm)-dna is in a smaller loop called a circular or bacterial chromosome-dna is naked-not associated with histone proteins-plasmids (smaller loops of dna) carry additional genes
- prokaryotic features-ATP production occurs in infolded parts of the cell surface membrane called mesosomes-some species have flagella for movement- similar to eukaryotic undulipodia but with a different structure
- cell wall (bacteria)-physical barrier which protects against mechanical damage
- capsule (bacteria)-protects bacterium from WBC and helps groups of bacteria to stick together
- plasma membrane (bacteria)-acts as a partially permeable layer to control entry and exit of substances
- pilus (bacteria)-helps cells stick to one another or to surfaces
- flagellum (bacteria)-aids movement through fluids by rotation
- prokaryotic cells are usually 0.1-5 micrometers in diameter, whereas eukaryotic are usually 10-100 micrometers
- prokaryotic cells have dna is located in a region called a nucleoid whereas in a eukaryotic cell, dna is found in chromosomes in the nucleus
- in a prokaryotic cell, flagella is present and in a eukaryotic cell, cilia and flagella can be present
- plant cell features-cellulose cell wall for strength and support-large, permanent, fluid-filled vacuole surrounded by a membrane called a tonoplast-chloroplasts for photosynthesis-plasmodesmata (gaps in cell wall) link adjacent cells together
- animal cell features-surrounded by a plasma membrane-jelly like cytoplasm containing organelles such as mitochondria, ribosomes, nucleus, golgi apparatus
- cilia and undulipodia (or flagella)-hair-like extensions from cells-allow movement-cilia- short, many found from 1 cell-cilia- trachea, bronchi and fallopian tubes-undulipodia- long, 1 or 2 from each cell-both have similar structure-microtubules arranged in pairs and slide past each other.
- vesicles and vacuoles-store food, water or waste molecules-vesicles- small membrane-bound sacs used for transportation (protein synthesis) within cells-large permanent vacuole- plants- surrounding membrane is called a tonoplast-plant cells vacuole remains turgor for support-vacuoles may be small or absent in animal cells
- chloroplasts-only found in plants and algae-chloroplasts contain pigment chlorophyll and accessory pigments which absorb light energy-double membrane-grana- stack of thylaloid discs that contain the chlorophyll molecule-stroma- fluid containing photosynthetic enzymes
- centrioles-2 short bundles of 9 microtubules arranged at right angles to each other-located just outside the nucleus in clear area of cytoplasm called centrosome-migrate to opposite ends of the cell during cell division to form spindle fibres to pull chromosomes to opposing ends of the cell
- cell wall-plant cells but not animal-provides strength and support-cellulose-allows water and dissolved molecules to pass through-pores called plasmodesmata connect cytoplasm of adjacent cells for more rapid exchange of molceules
- lysosomes-spherical sac bounded by a single membrane-contains digestive (hydrolytic) enzymes-intracellular digestion of food materials-help WBC destroy bacteria in process of phagocytosis-destroy worn-out organelles inside cells-for self- destruction of cells in developmental processes
- cell surface membrane or plasma membrane-outer boundary of animals cells. found in cell walls in plants-defines animal cell's perimeter-controls what enters and leaves the cell-place of communication with environment and other cells
- mitochondria-site of respiration-where molecule ATP is produced-long and thin-double membrane-matrix (liquid) and cristae (folds of inner membrane)-cristae increases the surface area for attachment of respiratory enzymes-many mitochondria in liver and muscle cells
- golgi body or golgi apparatus-stack of sac-like membranes usually located near the nucleus-transport vesicles pinch off from the sides-process, package and distribute proteins made within the cell-involved in secretion- hormones, enzymes, saliva, mucus- all have golgi bodies
- ribosomes-made of 2 protein sub-units- smallest organelle (22nm)-site of protein synthesis in cells-maybe be found free in cytoplasm or attached to RER-proteins vital to life- all cells must produce them
- nucleus-largest organelle-contains all genetic info in form of DNA-nucleolus- darker region where RNA and ribosomes are made-nuclear envelope- double membrane surrounding nucleus that is perforated by nuclear pores for exchange of materials between nucleus and cytoplasm
- endoplasmic reticulum-series of folded membranes- form interconnected sacs or tubes called cisternae-rough ER- ribosomes attached and is continuous with nuclear envelope- involved in protein synthesis and transport-smooth ER- no ribosomes and is site of lipid synthesis
- prokaryotic cells are usually 1-10 micrometres in diameter
- eukaryotic cells are usually 20-100 micrometres in diameter
- prokaryotic cells-no distinct nucleus-dna is circular-dna is naked-ribosomes are 18nm-ribosomes are free in cytoplasm-peptidoglycan cell wall-no membrane-bound organelles-atp production takes place in mesosomes-no microtubules in flagella
- eukaryotic cells-distinct nucleus surrounded by envelope of two membranes-dna is linear in chromosomes-dna is associated with histone proteins-ribosomes are 22nm-ribosomes are attached to Rough ER-cellulose cell wall-membrane bound organelles-atp production happens in mitochondria-flagella have 9+2 arrangement in microtubules