Structure and Function of cell organelle Flashcards
Describe the nucleus
Contains the cell’s genetic information and controls activities of the cell
Relatively large 2-10µm, spherical, centrally located
What are the key features of the nucleus
a) The genome of the organism. Only easily seen during cell division when chromatin strands coil and condense into thick ‘chromosomes’. Not random organisation - different territories.
b) Double layer membrane ‘nuclear envelope’ with pores to allow export of mRNA molecules/import of proteins. Nuclear pore complex controls passage.
c) Nucleolus. Visible in interphase nuclei, involved in production of ribosomal RNA to form ribosomes.
d) Shape maintained by protein skeleton ‘nuclear matrix’.
What is the endoplasmic reticulum
System of membranous tubules and sacs branching throughout cytoplasm
Two sorts: ‘Rough’ ER (studded with ribosomes) with primary function of ‘intracellular highway’ for molecule movement and modification
‘Smooth’ ER specialised for metabolism and storage
What are the key features of the Endoplasmic reticulum
a) Highly folded membrane system continuous with outer nuclear envelope. Has inner ‘lumen’ region.
b) Rough ER studded with ribosomes. Processes proteins to be exported from cell (acts with Golgi). Proteins with amino acid ‘signal sequence’ are directed into ER lumen.
c) Proteins chemically modified within ER e.g. proteins fold correctly; oligosaccharide side chains added to proteins. Internal lumen provides correct environment.
d) Smooth ER has few ribosomes. Instead has embedded transmembrane enzymes involved with production/processing of lipids and carbohydrates. Also synthesis of steroids, toxin breakdown in liver cells.
e) Main site of new membrane synthesis in cell.
f) Sequesters calcium within lumen.
How does the structure of the ER link to its function
Amount of ER varies according to cell activity. High levels in secretory cells
Describe the Golgi Apparatus
System of membrane sacs (cisternae) piled on top of each other (8 flattened pitta breads!) with associated vesicles (smaller sacs). Sacs nearest cell center called cis and those nearest plasma membranes are trans. Works closely with ER, which buds off vesicles that fuse with cis face.
Proteins are modified within Golgi, most common adds/modifies sugars. Passes through successive layers of cisternae by budding and fusing with next layer and/or layer maturation.
* Materials packaged into membrane-enclosed vesicles which pinch off from edges. Then either distributed within cell or shipped to PM for export. The ‘postal sorting office’ for the cell!
Describe the Lysosomes and Endosomes
- Inter-related single-membrane bound compartments in cell. Features:
- Vesicles containing digestive enzymes produced from ER/Golgi fuse and mature to form lysosome.
- Lysosome is essentially membrane-bound vesicles of digestive hydrolytic enzymes (up to 50!). Essentially “suicide bags” of destructive enzymes. Acidic pH5 for activity.
- Digest either incoming material e.g. endosomes, food vacuoles or engulfed cells OR digest internal material - enables organism to destroy old or malfunctioning cell parts/organelles.
- Commonly observed in animal, fungi, protist cells; rare in plants.
Specialized membrane with transporters to export digestion products. Also pumps in H+
What is the mitochondria
The powerhouse of the cell
Describe the structure of the mitochondria
- Small 1-4 µm x 0.2-1.0 µm. Similar to bacteria.
- Two membranes. Outer border and inner membrane. Latter has extensive invaginations ‘cristae’ to increase SA. Forms inner matrix and inter-membrane space.
- Numbers differ according to cell types. More numerous in cells with high energy requirements - e.g. muscle cells. Populations appear in state of continual flux, divide and fuse extensively, can form chains.
- Inner membrane embedded with metabolic proteins e.g. ATP synthase. Major source of ATP for cell through respiration.
- Mitochondria have own genome composed of set of circular DNA molecules. Encodes limited number, but not all, of genes for metabolic activities
What are plastids
Found only in plants and algae.
The most common is chloroplast
Describe the structure of the plastid chlorophyll
- 5-8 x 2-4 µm. Larger than mitochondria.
- Double membrane at border. Inner space ‘stroma’ with membrane sacks ‘thylakoids’ arranged in coin-like stacks called ‘grana’.
Chloroplasts contain chlorophyll. Protein photoreceptors on thylakoid membrane are site of photosynthesis and ATP production
How can other plastids differ from chlorophyll
- Other plastids lack chlorophyll and simpler structure. Used for storage e.g. leucoplast for starch storage.
- Plastids have distinct genome of circular DNA molecules. Encodes some, but not all, genes for metabolic activities.
Describe the vacuole
- Fluid-filled membrane-bound sac(s).
- Prominent structure in plant cells, up to 90% of space.
- Serves as storage area. Usually contain water and chemicals e.g. sugars, ions. Some plants have poisons to discourage herbivory, or pigments (petal colour), toxins cell cannot excrete
- Bounded by tonoplast membrane with proteins pumps which transport molecules into the vacuole.
- Plant cells provide high turgor pressure, which pushes against rigid cell wall to give cell strength.
Can animal cells have vacuoles?
Animal cells may contain vacuoles, but much smaller and usually involved in food digestion. Also contractile vacuole
What other cell components are there which are not membrane-bound
Ribosomes
Centrioles
Cytoskeleton
