General cell biology and cell organelles Flashcards

Question

Important metabolic functions of mitochondria:

Answer 1

*In the matrix:* - **Citric acid cycle** (metabolic center, synthesis of amino acids, oxidative degradation of pyruvate, the product of glycolysis) - **beta-Oxidation of fatty acids** (degradation to acetyl-CoA) * At the inner mitochondrial membrane:* * *Oxidative chain reaction** (cell respiration, ATP-synthesis by oxidation of NADH+H+, FADH2)

Answer 2

Plastits are: - larger - have an outer and inner, as well as a thylakoid membrane with grana - responsible for different metabolic processes

Answer 3

Same as mitochondria: - have their own DNA, ribosomes, and they divide

Answer 4

*at the thylakoid membranes*: **Photosynthesis** (ligth reaction, electron transfer reactions, chlorophyll, ATP-synthesis, NADP reduction) *in the stroma:* **Calvin-Cycle** (CO2 fixation in dark reaction, products of photosynthesis enter the cell metabolism, RUBISCO) Energy storage: starch

Answer 5

1. Mitochondrial DNA, circular structure, no histones, similar to bacterial DNA 2. Mitochondrial ribosomes similar to those of bacteria in size, compatibility of subunits 3. Double membrane 4. Composition of the inner membrane similar to bacterial membrane, details of protein biosynthesis, sensitivity to antibiotics, tRNAF-Met 5. Living model organisms

Answer 6

- floating freely in the cytosol - at the rough endoplasmic reticulum, rER - in plastids and mithochondria

Answer 7

large subunits: 60 S = 1/3 protein (49 molecules) + 2/3 rRNA (28S, 5,8S, 5S) small subunits: 40 S = 1/3 protein (33 molecules) + 2/3 rRNA (18S)

Answer 8

**Protein biosynthesis**: Membrane proteins, lysosomal proteins, exportable proteins; signal sequence in primary structure, SRP, docking of ribosomes, transcription, chaperones **Glykosylation of proteins**: at asparagine residues, transfer of an oligosaccharide from dolichol

Answer 9

**Posttranscriptional modification:** glycosylation Lipid synthesis: steroids, phospholipids, glycolipids, sphingomyelin of the membranes **Storage function:** Ca2+, proteins, lipids, glycogen

Answer 10

**Golgi complex:** • Membrane system: ER – Golgi - Lysosomes • Golgi cisterns, dictyosomes, transport vesicles **Functions of the Golgi complex:** - Transport and distribution within the cell: soluble proteins, membrane segments, vesicles of exo- and endocytosis - Modification and sorting of proteins: glycosylation, modification of oligosaccharide side chains - Production of lysosomes: intracellular degradation

Answer 11

Found within the cytoplasm of both plant and animal cells, the Golgi is composed of stacks of membrane-bound structures known as cisternae (singular: cisterna). An individual stack is sometimes called a dictyosome (from Greek dictyon: net + soma: body),[4] especially in plant cells.[5] A mammalian cell typically contains 40 to 100 stacks.[6] Between four and eight cisternae are usually present in a stack; however, in some protists as many as sixty have been observed.[3] Each cisterna comprises a flat, membrane enclosed disc that includes special Golgi enzymes which modify or help to modify cargo proteins that travel through it.[7] The cisternae stack has four functional regions: the cis-Golgi network, medial-Golgi, endo-Golgi, and trans-Golgi network. Vesicles from the endoplasmic reticulum (via the vesicular-tubular clusters) fuse with the network and subsequently progress through the stack to the trans Golgi network, where they are packaged and sent to their destination. Each region contains different enzymes which selectively modify the contents depending on where they reside.[8] The cisternae also carry structural proteins important for their maintenance as flattened membranes which stack upon each other.[9]

Answer 12

The Golgi apparatus is integral in modifying, sorting, and packaging these macromolecules for cell secretion[10] (exocytosis) or use within the cell.[11] It primarily modifies proteins delivered from the rough endoplasmic reticulum but is also involved in the transport of lipids around the cell, and the creation of lysosomes.[11] In this respect it can be thought of as similar to a post office; it packages and labels items which it then sends to different parts of the cell. Enzymes within the cisternae are able to modify the proteins by addition of carbohydrates (glycosylation)[12] and phosphates (phosphorylation). In order to do so, the Golgi imports substances such as nucleotide sugars from the cytosol. These modifications may also form a signal sequence which determines the final destination of the protein. For example, the Golgi apparatus adds a mannose-6-phosphate label to proteins destined for lysosomes. The Golgi plays an important role in the synthesis of proteoglycans, which are molecules present in the extracellular matrix of animals. It is also a major site of carbohydrate synthesis.[13] This includes the production of glycosaminoglycans (GAGs), long unbranched polysaccharides which the Golgi then attaches to a protein synthesised in the endoplasmic reticulum to form proteoglycans.[14] Enzymes in the Golgi polymerize several of these GAGs via a xylose link onto the core protein. Another task of the Golgi involves the sulfation of certain molecules passing through its lumen via sulfotranferases that gain their sulfur molecule from a donor called PAPS. This process occurs on the GAGs of proteoglycans as well as on the core protein. Sulfation is generally performed in the trans-Golgi network. The level of sulfation is very important to the proteoglycans' signalling abilities as well as giving the proteoglycan its overall negative charge.[13] The phosphorylation of molecules requires that ATP is imported into the lumen of the Golgi[15] and utilised by resident kinases such as casein kinase 1 and casein kinase 2. One molecule that is phosphorylated in the Golgi is Apolipoprotein, which forms a molecule known as VLDL that is a constituent of blood serum. It is thought that the phosphorylation of these molecules is important to help aid in their sorting for secretion into the blood serum.[16] The Golgi has a putative role in apoptosis, with several Bcl-2 family members localised there, as well as to the mitochondria. A newly characterized protein, GAAP (Golgi anti-apoptotic protein), almost exclusively resides in the Golgi and protects cells from apoptosis by an as-yet undefined mechanism.[17]

Answer 13

* Degradation and intracellular recycling of lipids, sugars and proteins; pH 5 (cytosol: pH 7.2; proton pumps in the membrane) * Enzymes: acidic hydrolases (lipases, proteases, glycosidases, phosphatases, sulfatases, phospholipases; A-B + H2O A-H + B-OH; A-B: ester bond, peptide bond, glycosidic bond)

Answer 14

**Heterolysosomes** Phagocytosis by single cell organisms, macrophages, leukocytes in the immune system **Autolysosomes** normal turn over of organelles: e.g. mitochondrial halflife in the liver is only 10 d; processes of regeneration, metamorphosis Aging pigment, non-degradable residues in lysosomes: lipofuscin

Answer 15

**Autolysis (rare):** toxins of bacteria, ureic acid cristals in gout, asbestos particles in the lungs: disruption of membranens, destructive enzymes are released into the cytosol **Lysosomal storage diseases:** accumulation of filled lysosomes, whose content can not be degraded due to the lack of certain enzymes, results in cell death Examples: - Tay-Sachs-Disease (autosomal recessive, ganglioside GM2, mental retardation, high incidence in Ashkenazi jews) - I-Cell-Disease (lack of many enzymes in the lysosomes of fibroblasts, no phosphorylation of mannose, thus defective targeting, enyzmes go into the blood instead, inclusion bodies in fibroblasts)

Answer 16

Properties: * Vesicles with membranes, d = ca. 0.5 μm (microbodies) * contain oxidases, characteristic enzyme: catalase Functions: Catalase reaction: 2 H2O2 2 H2O + O2 Participate in: • oxidation of fatty acids to acetyl-CoA (-oxidation in mitochondria) • amino acid metabolism • degradation of N-containing bases of nucleic acids: - adenine to xanthine guanine to hypoxanthine to ureic acid to allantoin (most mammals; in humans secretion of ureic acid)

Answer 17

* Multi enzyme complexes (not surrounded by membranes) * characteristic structure: barrel with lid * second pathway of protein degradation: ubiquinilation as signal