Lecture 9 - Cells and Organelles

Question 1

compartmentalization

Answer 1

• define boundaries of a cell and organelles

Question 2

scaffolding for biochemical activities

Answer 2

• can provide a framework that organizes enzymes for effective interactions

Question 3

energy transduction

Answer 3

• membranes transduce photosynthetic energy, convert chemical energy to ATP and store energy

Question 4

what is the nuclear structure

Answer 4

• inner membrane defines the nucleus
• outer membrane is contiguous with the ER
• nuclear pores fuse the 2 membranes and they serve as a conduit for transport between the cytoplasm and nucleoplasm

Question 5

what is the contained in the nucleus

Answer 5

• molecules of DNA organized into chromosomes

Question 6

what is the nucleolus

Answer 6

• structure where rRNA is transcribed and ribosome subunits are assembled

Question 7

what is the structure of the endoplasmic reticulum

Answer 7

• tubular membranes and flattened sacs called cisternae
• internal space of ER is the lumen
• ER is continuous with the outer membrane of the nuclear envelope

Question 8

what is the function of the rough ER

Answer 8

• critical starting starting point of the protein biosynthetic pathways
• cytoplasmic side is studded with ribosomes
• the ribosomes synthesize polypeptides that are inserted into the ER membrane or are transported into the ER lumen

Question 9

what is the function of the smooth ER

Answer 9

• extensively developed in many cells
• no role in protein synthesis
• synthesis of lipids and steroid hormones -> prominent in gonad and adrenal cortex endocrine cells
• detoxification in liver of many organic compounds
• a type of smooth ER, sarcoplasmic reticulum, is critical for storage and release of calcium ions during muscle contraction

Question 10

what is the structure of the golgi complex

Answer 10

• closely related to ER in proximity and function
• consists of a stack of flattened vesicles -> cisternae
• transport vesicles from the rough ER fuse with the cis region and deposit their protein contents -> as the proteins pass through the golgi they are further processed and modified
• vesicles then bud off from the trans golgi network

Question 11

what is the function of the golgi complex

Answer 11

• plays an important role in processing and packaging secretory proteins, and in complex polysaccharide synthesis
• TGN (trans golgi network) vesicle sorting station
• CGN (cis golgi network) transition vesicle sorting station

Question 12

what happens in the cisternae of the golgi

Answer 12

• proteins/lipids are glycosylated finishing a post-translational modification (PTM) process that began in the ER

Question 13

what is the structure of lysosomes

Answer 13

• they are the digestive organelle
• single membrane and store approx. 50 hydrolases
• break down macromolecules
• hydrolases are synthesized in the ER, transported to the golgi, and then targeted to the lysosomes
• very heterogenous morphology
• enzymes are pH activated and sequestered to prevent them from digesting the contents of the cell

Question 14

what is the function of lysosomes

Answer 14

• an ATP driven H+ pump in the lysosomal membrane maintains the low internal pH
• a special carbohydrate coating on the inner side of the lysosome membrane protects it from digestion
• lysosomal membrane also contain transport proteins that transport the products of macromolecule digestion to the cytosol for reuse or excretion

Question 15

what are the 3 degradation pathways utilizing the lysosome

Answer 15

1. endocytosis
2. phagocytosis
3. autophagy

Question 16

what is the autophagic pathway

Answer 16

• digestion of cytoplasm and worn-out organelles by the cells own lysosomes
• increase under starvation conditions
• ATP genes are required for this process

Question 17

what are secretory vesicles

Answer 17

• once processed by the golgi material to be exported from the cell are packaged into secretory vesicles
• move to the plasma membrane and fuse with it -> releasing their contents outside the cell by exocytosis
• ER, golgi, vesicles, lysosomes make up the endomembrane system -> responsible for trafficking substances through the cell

Question 18

what is exocytosis

Answer 18

• proteins leave the cell (hormones, growth factors)
• molecules are added to the plasma membrane (receptors, lipid components )

Question 19

what is endocytosis

Answer 19

• cellular uptake of particles and macromolecules
• nutrients, growth factors, recycling of membrane, membrane repair

Question 20

what are peroxisomes

Answer 20

• cytoplasmic vesicles
• surrounded by a single membrane and perform several functions depending on cell type
• not part of the endomembrane system
• prominent in liver and kidney cells

Question 21

what are the functions on peroxisomes

Answer 21

• detoxify harmful compounds and catabolize unusual substances
• in animals they play a vital role in oxidative breakdown of fatty acids, especially longer fatty acids
• human diseases result from defects in peroxisomal enzymes normally involved in degrading long chain fatty acids
• can both generate and degrade hydrogen peroxide

Question 22

explain more about peroxisomes and hydrogen peroxide

Answer 22

• cells protect themselves by performing H2O2 generating reactions in the same organelle as catalase
• contain enzymes that use molecular oxygen to remove hydrogen atoms from specific organic substances = oxidases

Question 23

what are the 2 membrane structures of the mitochondria

Answer 23

1. outer membrane - relatively permeable, contains porins which allow free movement of small molecules and ions across the outer membrane
2. inner membrane - highly impermeable, acts as a permeability barrier to most solutes
   - highly folded into cristae that project into the interior of the mitochondria
   - respiratory proteins are embedded in the inner membrane
   - the density of cristae is related to the respiratory activity of a cell
   - where ATP is made

Question 24

what are the 3 regions of the mitochondria

Answer 24

1. matrix - within the inner membrane, contains most of the enzymes associated with mitochondrial function in addition to DNA and ribosomes
2. intermembrane space - area between the outer and inner membranes
3. intracristal space - localized regions where protons can accumulate during the electron transport process

Question 25

what is the structure of the mitochondria

Answer 25

- genome is 16569 base pairs long, encodes 37 genes, and encodes about 5% of all the RNAs and proteins needed by the mitochondrion - a single subunit RNA polymerase - 2 rRNA transcripts - 22 tRNA - small number of polypeptides (13 in humans)

Question 26

what is the function of the mitochondria

Answer 26

- principle site of ATP production in non-photosynthetic cells - number and location of mitochondria varies among cells according to their role in that cell type - tissues with high demand for ATP have many mitochondria, located within the cell at the site of greatest energy needs - important in the regulation of apoptosis

Question 27

what is the structure of chloroplast

Answer 27

- found in the leaves of green plants - surrounded by inner and outer membrane - similar to mitochondrial membrane regarding permeability - contain a system of flattened membranous sacs called thylakoids, stacked into grana - stroma contains a larger circular genome

Question 28

what is the function of chloroplast

Answer 28

- site of photosynthesis, this process is the reverse of the mitochondrial reactions that oxidize glucose into CO2 - chloroplasts found in photosynthetic cells and contain most of the enzymes needed for photosynthesis - reactions that depend on solar energy take place in or on the thylakoid membranes - reactions involved in the reduction of CO2 to sugar occur within the stroma

Question 29

what is the endosymbiont theory

Answer 29

- mitochondria and chloroplasts have their own DNA and ribosomes - they can produce some of their own proteins but many are encoded by nuclear genes - many similarities between processes in mitochondria and chloroplast and those in bacteria - proto-eukaryotes may have ingested bacteria by phagocytosis without then digesting them allowing a symbiotic relationship to develop

Question 30

similarities between mitochondria, chloroplasts, and bacteria

Answer 30

- some resemble bacteria in size and shape - surrounded by double membranes, the inner of which has bacterial-type lipids - circular DNA with no histones - rRNA sequences, ribosome size and the type of protein factors used in protein synthesis are all similar to bacteria - mitochondria/chloroplasts are sensitivities to bacterial inhibitors of RNA and protein synthesis

Question 31

what are vacuoles

Answer 31

- 90% of plant cell can be occupied by vacuoles - fluid filled structures are surrounded by single membrane - tonoplast contains a number of active transporters, ac vacuoles can store ions, amino acids, proteins, and polysaccharides - toxic compounds are stored in plant vacuoles as the cell wall can impair excretion of waste - in plant cells the main function of the central vacuole is to maintain the turgor pressure that keeps the plant from wilting

Question 32

what is the endomembrane system comprised of

Answer 32

- ER - Golgi complex - Lysosomes - vesicles