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Mitochondria
membrane-bounded organelles found in most eukaryotic cells, that convert energy derived from glucose and other nutrient molecules into ATP
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Mitochondria have their own DNA, separate from the _______ ______. The mitochondrial genome encodes some, but not all, of the proteins needed for ______ _______. The remainder are encoded by the ______ ______ and imported into the organelle
- nuclear genome
- energy conversion
- nuclear genome
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The unwrinkled outer membrane surrounds an inner membrane (of mitochondria) bent into wrinkles called _______. The inner membrane in turn surrounds an area called the ________
- cristae
- matrix
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Mitochondria produce packets of energy (ATP) in two stages: (broad strokes)
- First, enzymes in the matrix catalyze the Krebs cycle, which metabolizes pyruvate and fatty acids to produce the high-energy electrons carriers NADH and FADH2
- Second, a series of multisubunit enzyme complexes embedded in the inner mitochondrial membrane harness this energy in a process called oxidative phosphorylation
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Some of the enzyme complexes form an ______ ________ ______ that transfers the electrons from NADH and FADH2 to the ultimate electron acceptor, _______. The energy released from these steps of electron transport is used to pump protons out of the _______ into the space between the ______ and ______ membrane, creating an _______ potential across the ______ membrane
- electron transport chain
- oxygen
- matrix
- inner and outer membranes
- electrical
- inner
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The protons then flow back into the _______ through an enzyme complex called _____ ________, which is embedded in the _______. ATP synthase uses the energy released by this flow of protons to ________ ADP and thus form ______
- matrix
- ATP synthase
- cristae
- phosphorylate
- ATP
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A single mitochondrion usually contains several ______ of its genome within the matrix; the number of _____ can vary depending on the _______ needs of the cell, but is usually between 2 and 10
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The 16.5 kb human mitochondrial genome, which is only 1/100,000th the length of the haploid genome in a human gamete, is a ________ DNA molecule that carries ____ genes. Thirteen of these genes encode _______ subunits of the protein complexes that make up the _______ _______ apparatus. The mitochondrial genome also encodes 22 _____ genes and 2 genes for the large and small ______ found in mitochondrial ribosomes
- circular
- 37
- polypeptide
- oxidative phosphorylation
- tRNA
- rRNAs
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A significant feature of the human mitochondrial genome is the _______ of its gene arrangement. Adjacent genes either _____ each other or in few cases, even slightly ______. With virtually no nucleotides between them and no _______ within them, the genes are packaged very _______
- compactness
- abut
- overlap
- introns
- tightly
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Protozoans parasites of the genera Trypanosoma and Leishmania exhibit mtDNAs that have a highly unusual ________. These _______-celled euk organisms carry a single mitochondrion known as a ________. Within this structure, the mtDNA exist as a large network of 10-25,000 ______ 0.5-2.5 kb in length interlocked with 50-100 ______ 21-31 kb long
- organization
- single-celled
- kinetoplast
- minicircles
- maxicircles
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Researchers discovered the unexpected phenomenon of RNA editing in the mitchondrion (______) of trypansomes. DNA sequencing of maxicircle DNA, minicircle DNA and cDNAs copied from ______ mRNAs revealed major surprises
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The minicircles did not encode any _____ ______ genes, while the maxicircles contained gene sequences that were clearly ______, but far from ______, to the cDNAs corresponding to the protein-coding mRNAs. These results imply that the maxicirlces are transcribed into _____ _____ that are then changed into _______ ______
- protein-coding genes
- related
- idnetical
- precursor RNAs (pre-mRNAs)
- mature mRNAs
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RNA editing
A special type of transcript processing that converts pre-mRNAs to mature mRNAs
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Without RNA editing, the____-_____ do not encode polypeptides. Some pre-mRNAs lack a ______ _____ suitable for translation initiation; others lack a ______ ______ for the termination of translation. _____ _____ creates both types of sites, as well as many new codons within the genes
- pre-mRNAs
- first codon
- stop codon
- RNA editing
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In trypanosomes, the RNA editing machinery adds or deletes _______ to convert pre-mRNAs into _____ ______. We see _____ editing occurs in stages in which enzymes organized into a structure called an _______ use an _____ template as a guide for correcting the _____. Explain why kinetoplasts have minicircles as well as maxicircles
- uracils
- mature mRNAs
- uracil
- editosome
- RNA
- pre-mRNA
- The maxicircles are transcribed into pre-mRNAs which are converted into mature mRNAs (via RNA editing) using guide RNAs which are transcribed from short stretches of DNA on minicircles
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Mitochondria have their own distinct translational apparatus, as suggested by the fact that mtDNAs carry their own _____ and _____ genes. Mitochondrial translation is quite unlike the cytoplasmic _______ of mRNAs _______ from nuclear genes in euks; in fact, many aspects of the mitochondrial translation system resemble details of translation in _______.
- rRNA and tRNA genes
- translation
- transcribed
- prokaryotes
- *For example, as in bacteria, N-formyl methionine and tRNAfMet initiate translation in mitochondria
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Moreover, drugs that inhibit bacterial translation, such as chloramphenicol and erythromycin, which have no effect on _____ cytoplasmic protein synthesis, are potent ______ of mitochondrial protein syntehsis
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Many exceptions to the "universal" code involve mitochondria. For example, in human mt DNA, five triplets are used differently than they would be in the ______. No single mitochondrial ______ _____ functions in all organisms, and the mitochondria of higher plants use the ______ _____. How did the genetic code of some mitochondria diverge from the universal code?
- nucleus
- genetic code
- universal code
- By a series of mutations occurring some time after the organelles became established components of euk cells
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Chloroplasts capture _____ _____ and store it in the chemical bonds of _____ through the process of _______. Every time a bird takes flight, a person speaks, a worm turns etc, the organism's cells are using _____ that was originally captured from _____ by _______ and is then released through the functions of ________
- solar energy
- carbs
- photosynthesis
- energy
- sunglight
- chloroplasts
- mitochondria
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Embedded in the membranes of internal structures called _______ are the light-absorbing pigment ______ and light-absorbing proteins, as well as proteins of the photosynthetic _______ _______ system
- thylakoids
- chlorophyll
- electron transport system
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During the light-trapping phase of photosynthesis, energy of photons of light from the _____ boosts electrons in ________ to higher energy levels. The energized electrons are then conveyed to an _______ ______ system that uses the energy convert water to _____ and ______
- sun
- chlorophyll
- electron transport
- oxygen and protons
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Photosynthetic electron transport forms _______ and drives the synthesis of _____ via an _____ ______ similar to the one mitochondria. During the second, ______-building phase of photosynthesis, enzymes of the Calvin cycle use that _____ and _______ to convert atmospheric carbon dioxide into _________. The energy stored in the ______ of these nutrient molecules fuels the activities of both the plants that make them and animals that eat the plants
- NADPH
- ATP
- ATP synthase
- sugar-building
- ATP and NADPH
- carbohydrates
- bonds
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Chlroplasts occur in _____ and _____. The genomes they carry are much more _______ in size than the genomes of mitochondria. Although chloroplast DNAs (cpDNAs) range in size from 10 to 217 kb, most are between 120 and 160kb long. cpDNA contains many _____ genes than mtDNA
- plants and algae
- uniform
- more
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Like the genes of bacteria and human mtDNA, these genes are ______ packed, with relatively few nucleotides _______ adjacent coding sequences. Like the genes of yeast (but no human) mtDNA, they contain _______. Although some are ______, many cpDNAs exist as _______ and ______ forms. Like mitochondria, chloroplasts contain more than one copy of their _______ (usually 15-2
genome copies)
- closely
- between
- introns
- circular
- linear
- branched
- genome
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The chloroplast genome of the liverwort M. polymorpha, the first cpDNA to be sequenced completely, is depicted. The cpDNA-encoded proteins include many of the molecules that carry out photosynthetic ______ ______ and other aspects of _________, as well as RNA polymerase, translation factors, ribosomal proteins, and other molecules active in chloroplast gene ________
- electron transport
- photosynthesis
- expression
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The RNA polymerase of chloroplasts is similar to the multisubunit _______ _____ ______. Drugs that inhibit bacterial _______, such as chloramphenicol and streptomycin, inhibit _______ in chloroplasts, as they do in mitochondria
- bacterial RNA polymerase
- translation
- translation
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Its hard to get mutants into organelle genes so they came up with the gene gun. How does it work?
- You make some sequence that is the gene you want to modify in mitochondria (with a few mutations/differences)
- They coat it with a pellet and shoot that toward the cells where the pellet hits a screen, stopping the pellet but propelling the DNA toward the cell at high speeds (some of DNA might make it into the mitochondria)
- Not a huge success rate but it’s the best method available
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Endosymbiont Theory (3-story)
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Variegated plants typically have branches that are variegated with some parts ______ and some ______, and also branches that are either solid ______ or ______. Carl Correns performed all nine possible pairwise crosses between male (pollen) and female (ova) gametes from flowers growing in each type of branch: _______, _____ or ______. The progeny phenotypes always resembled that of the source of the ______ gamete because the color of the plant cells is controlled by _______ _____ _____
- green
- white
- green or white
- variegated, green or white
- female
- maternally inherited cpDNA
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The reason for the variegated phenotype is that variegated four-o'clocks have ____ kinds of chloroplasts (name them). The mutant cpDNAs have a defective allele of a gene required for synthesis of the green pigment ______; cells without _______ are white. A cell or organism with more than one genotype of an organellar genome is said to be _________
- two kinds: wild-type and mutant
- chlorophyll
- chlorophyll
- heteroplasmic
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Why is the variegated plant considered as a whole to be heteroplasmic?
The plant also has homosplasmic cells (define).
- because it came from a heteroplasmic egg, one that contained both wild-type and mutant chloroplasts.
- Homoplasmic cell: cell with with only one type of cpDNA. *For example, the solid white areas of the plant are homoplasmic for mutant chloroplasts
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When a cell undergoes mitosis, a ______ half (approx.) of the chloroplasts end up in each daughter cell. It is easy to see that after several cell divisions in which _____ and _____ ____ chloroplasts are, ______ distributed _________ in the two daugher cells, a _________ daughter cell containing only one type of cpDNA could arise from an originally ________ cell by random _______ _________
- random
- mutant and wild-type
- random
- unequally
- homoplasmic
- heteroplasmic
- cytoplasmic segregation
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Once a cell becomes _______, it cannot become ________ again (except by new mutation), and so all of its descendants from that point are ___________. Chance ________ ________ of chloroplasts explains at least in part how a plant that is heteroplasmic for wild-type and mutant chloroplasts could have a mixture of heteroplasmic, homosplasmic wild-type and homoplasmic mutant cells
- homoplasmic
- heteroplasmic
- homoplasmic
- cytoplasmic segregation
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Variegated plants usually have a variegated main shoot with ______ of green and white tissue, and also branches that are _____ green or ______ white. In the variegated regions, the green patches contain mainly ________ cells. During mitosis, cells _______ for mutant chloroplasts can arise and they establish the white patches and also white branches. Cells _______ for wild-type chloroplasts also arise and establish the solid green branches
- patches
- solid
- solid
- heteroplasmic
- homoplasmic
- homoplasmic
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In four-o'clocks, heteroplasmic cells are green (why?)
Define threshold effect
- because the amount of chlorophyll, even in a small number of wild-type chloroplasts, is still sufficient for green color
- Threshold effect: a phenomenon in which a particular fraction of wild-type organelles is sufficient for the normal phenotype
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The precise fraction of wild-type organelles needed to avoid a mutant phenotype will depend on the particular ______ and ______
gene and mutation
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Explain why female gametes from flowers on white branches are homoplasmic for mutant chloroplasts.
Flowers from green branches give rise to eggs homoplasmic for wild-type chloroplasts and therefore _____ _____ (non-variegating) progeny. Finally, flowers from variegated branches can have any one of the ______ _____ types. The plant depicted came from heteroplasmic egg of a flower from a variegated branch.
- they always give rise to solid white plants (which ultimately die because they cannot photosynthesize)
- solid green
- three egg types
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Each chloroplast or mitochondrion may have several copies of its ______, so individual organelle can itself be either ________ or ________ for wild-type versus mutant DNAs
- genome
- heteroplasmic or homoplasmic
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Two kinds of events can lead to cytoplasmic segregation of the genome within an originally heteroplasmic organelle. (Name them)
pg 504 upper left
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Whether or not an individual organelle will function normally (wild-type) or not (mutant) is potentially subject to ______ effects. Therefore, just like the cells they inhabit, the phenotype of an individual organelle (whether it is functionally wild-type or mutant) is affected by its relative fractions of ____ _____ and _______ _______ copies
- threshold effects
- wild-type and mutant genome copies
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how did researchers analyze the inheritance pattern of mtDNA in yeast?
pg 505 top left
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The experiment also shows that organelles from the parental cells of different mating types segregated during the ______ _______ of vegetative growth. Immediately after mating, the diploids would contain _____ ____ of mitochondria, and the diploid cells would all be phenotypically ____ because hat allele is dominant
- mitotic divisions
- both kinds
- Cr
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But after several rounds of division, some cells contained only _____ mitochondria and were thus phenotypically _____. Clearly the Cs and Cr mtDNAs underwent _______ cytoplasmic segregation
- Cs
- Cs
- random cytoplasmic segregation
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One aspect of S. cerevisiae biology makes this process of cytoplasmic segregation of mtDNAs so rapid that is often achieved only a ____ rounds of _____.
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This yeast divides mitotically through a process of budding that creates a ____ bud from a ______ mother cell. Because of this inequality in _____, only a few mtDNA molecules are transferred into the newly formed bud, making it _____ likely that the bud will contain mostly or only one type of mtDNA
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Leber's heredity optic neuropathy, or LHON, is a disease in which flaws in the ________ ______ ________ ______ lead to _____ ______ degeneration and ________. Family pedigrees shown that LHON passes only from _______ to offspring. LHON is caused by ________ mutations in any one of three mitochondrial genes (ND1, ND4, or ND6) each of which encodes a different subunit of the enzyme NADH dehydrogenase, the first enzyme in the ______ ______ pathway
- mitochondrial electron transport chain
- optic nerve
- blindness
- mother
- hypomorphic mutations
- electron transport pathway
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Diminished ______ flow down the respiratory transport chain reduces the mitochondrion's production of _____, causing a gradual ______ in cell function and ultimately cell ______.
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Why is it that in most people affected by LHON the optic nerves cells are homoplasmic for the disease mutation (all the mitochondria are mutant); what does this usually mean for taht person?
because the disease-causing alleles are weak mutants
usually this means that the person as a whole is homoplasmic for mutant mitochondria
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For this reason, LHON often (not always) shows the _______ possible inheritance pattern for a mitochondrial disease; all the mtDNAs in the ova of every affected female are ______, so all of their progeny (male and female) are ________ for mutant mitochondria
- simplest
- mutant
- homoplasmic
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People with a rare inherited condition nown as myoclonic epilepsy and ragged red fibeer disease (MERRF) have a range of
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