Cell Structure Flashcards
Recognise and describe structure and functions of rough and sooth endoplasmic reticulum, Golgi body, mitochondria, ribosomes, lysosomes, chloroplasts, cell surface membrane, nuclear envelope, centrioles, nucleus and nucleolus
Cell theory
- Cell is the fundamental unit of structure and function
- All cells arise from pre-existing cells by division
- Metabolism occurs within cells involving biochemical reactions
- Cells contain hereditary information (DNA) passed from parent to daughter cell during cell division
- Similar species have cells with similar chemical composition
- Living things made up of one or more cells
- Activity of organism depends on the total activity of independent cells
Magnification
Degree to which the viewed image is larger than the specimen
Resolution
Minimum distance whereby two points can be distinguished as separate
Transmission electron microscope
Study internal structures
Scanning electron microscope
Study surface of cells -> 3D image
Cell fractionation
Cells homogenised -> centrifuge separates organelles based on size/density
Size of organelles (micrometer) Nucleus Chloroplast Mitochondrion Lysosome Centrioles Ribosome
Nucleus: 5-10 Chloroplast: 5-10 Mitochondrion: 1-5 Lysosome: 0.2-1.0 Centrioles: 0.3-0.5 Ribosome: 0.02 (20nm)
Overview of cell structure (4)
- Plasma membrane/cell surface membrane
- Nucleus
- Cytoplasm -> Cytosol + organelles + cytoskeleton (framework of protein filaments that give cells their shape)
- Cell wall
Nucleus structure
Spherical
Nuclear envelope -> double membrane + nuclear pores
Chromosomes/chromatin -> DNA + histones -> euchromatin (loosely coiled, active) + heterochromatin (tightly coiled, not active)
Nucleus function
- Contains hereditary material (DNA) of organism
2. Controls activities of the cell by regulating protein synthesis
Nucleolus structure
Densely stained granules
One or more nucleoli per nucleus
Large concentration of DNA, rRNA and proteins
Nucleolus function
Synthesis of rRNA
Assembly of rRNA and ribosomal proteins into ribosomal subunits
Ribosome structure
Small subunit + large subunit
Ribosomal RNA + proteins
1. Freely floating in the cytosol (free ribosomes)
2. Attached to outer surface of rER (bound ribosomes)
Prokaryotes -> 70S
Eukaryotes -> 80S
Ribosome function
Protein synthesis -> translation of mRNA to protein
Free ribosomes -> proteins that function within cytosol
Bound ribosomes -> proteins for:
1. Secretion out of cell
2. Packaging within organelles
3. Insertion into membrane
Endomembrane system (5)
- Nuclear envelope
- Endoplasmic reticulum (ER)
- Golgi Apparatus
- Lysosome + Vesicles
- Plasma membrane
Nuclear envelope structure + function
Perforated by numerous nuclear pores, continuous with ER
Allow regulated passage of substances into or out of the nucleus
Endoplasmic reticulum structure
Extensive network of membranous tubules and sacs called cisternae
Rough endoplasmic reticulum structure
Bound ribosomes that stud outer surface -> rough
Signal peptide recognised by signal recognition particle -> bring ribosome to rER -> receptor protein
Cisternae flattened than sER
Rough endoplasmic reticulum function (4)
- Proteins synthesise by bound ribosomes fold into native 3D conformation as they enter cisternal space
- Glycosylation (add carbs) to form glycoproteins
- Transport of proteins in transport vesicles
(i) Secretion out of the cell
(ii) Packaging into organelles
(iii) Targeted for insertion into plasma membrane - Membrane factory -> grows by adding membrane proteins and phospholipids to own membrane -> transferred in the form of transport vesicles
Smooth endoplasmic reticulum structure
Appears smooth as it lacks bound ribosomes
Cisternae more tubular
Smooth endoplasmic reticulum function (4)
- Synthesise carbohydrates and lipids
- Break down glycogen to glucose in liver cells
- Detoxify drugs and poison in liver cells
- Store Ca2+ ions in muscle cells
Golgi apparatus structure
Cisternae + Golgi vesicles
Convex/’cis’ face -> vesicles fuse with it
Concave/’trans’ face -> vesicles pinch off
Golgi apparatus function (5)
Modifying, sorting and packaging
- Glycosylation -> glycoproteins and glycolipids
- Modify/cleave existing glycoproteins and glycolipids
- Form lysosomes
- Produce polysaccharides
- Sorts and targets completed material to different parts of the cell or for secretion
Lysosome structure
Single membrane
Hydrolytic enzymes made by bound ribosomes on rER and processed in GA -> bud off from there
Acidic
Lysosome function (4)
- Digestion of material taken in by endocytosis -> fuse with vesicles/vacuoles
- Autophagy -> breakdown of unwanted structures
- Release enzymes outside cell by exocytosis
- Autolysis -> contents of many lysosomes released within the cell simultaneously
Useful products absorbed into cytoplasm;
Unwanted products released into external medium by exocytosis
Mitochondrion structure
Rod-shaped
Double membrane
Outer membrane smooth
Inner membrane highly unfolded to form numerous cristae
-> large surface area
Matrix + inter membrane space
Contains 70S ribosomes, circular DNA and enzymes
Mitochondrion function
Site of cellular respiration -> generate ATP
Krebs cycle in matrix, oxidative phosphorylation in cristae
Chloroplast structure
Lens shaped
Double membrane
Thylakoids -> grana (stacks)
Chlorophyll, photosynthetic pigments, enzymes, photosystems on thylakoid membrane
Stroma contains circular DNA, ribosomes, enzymes and starch grains
Chloroplast function
Site of photosynthesis
Vacuole structure
Large vesicles derived from ER and GA
Fluid-filled sac bound by single membrane
Animal -> smaller and more numerous
Plant -> large central vacuole (tonoplast) which contains cell sap
Vacuole function
Animal
Food vacuoles formed by phagocytosis enclose material for digestion by lysosome
Fresh water protists -> contractile vacuoles -> pump excess water out
Plant Maintain turgor pressure Cell growth -> increase with minimal increase in cytoplasm Store waste products Food storage in seeds
Microtubule structure
Hollow rods (25nm diameter) Globular protein (tubulin) -> dimer (2 subunits) Stiff and run straight course
Microtubule function (4)
- Help maintain shape of cell (cytoskeleton)
- Intracellular transport
- Chromosome movement in cell division (spindle fibres)
- Structural component of centrioles, cilia and flagella
Centrioles structure
Pair of cylindrical, rod-like structures positioned at right angles
9 triplets of microtubules arranged in a ring
Found in region known as centrosome
Absent in higher plant cells (Microtubule organising centre)
Centrioles function
Replicate during cell division
Play role in nuclear division by helping to organise formation of spindle fibres, needed for separation of chromosomes
