Lecture 008s2 part 2
Protein Synthesis, Genetic Code, Mutation and Gene Exp, Gen of Chloroplasts & Mito
1. Protein Synthesis, Genetic Code, Mutation, Gene Expression and the Genetics of Chloroplasts &
Mitochondria
a. Endosymbiont theory: proposes that chloroplasts and mitochondria originated when free-living
bacteria were engulfed by primitive nucleated cells. Host- and guest-formed cellular
communities in which each member adapted to the group arrangement and derived benefit.
b. What will be different in the genetics of chloroplasts and mitochondrion?
i. Rules for transmission of organellar genomes can vary in different organisms and are
quite different from nuclear genomes.
ii. Surprisingly, the function and upkeep of organelles requires input and cooperation from
both the organellar genomes and the nuclear genomes (in the same cell).
iii. The biochemical processes and genomes of organelles resemble bacteria more than
eukaryotic cells – the basis for the endosymbiont theory.
2. MITOCHONDRIA
a. Mitochondria: organelles that covert energy derived from nutrient molecules into ATP;
mitochondria have their own genomes.
b. Mitochondria found in most eukaryotic cells.
c. Mitochondria have their own DNA separate from _________________________________.
d. Produce most of the cell’s usable energy in the form of ATP molecules.
e. The mitochondrial genome encodes SOME, but not ALL, of the proteins needed for _________
__________________________. What codes for the rest?
f. Each eukaryotic CELL houses MANY mitochondria (determined by cell energy demand) and
chance distribution during cytokinesis.
g. Mitochondrial DNA appears in the organelle in highly condensed structures called nucleoids.
h. Mitochondrial reproduction: similar to bacterial cells. They double their size, replicate their
DNA (2-10 copies of the mitochondrial DNA in each nucleoid) and then undergo fission (like
cleavage furrow) to produce two daughter mitochondria.
i. At cell division: mitochondria are distributed _________________ and _________________ to
the daughter cells (independent from what is occurring in the nuclear genome).
j. RESULT of passive and random distribution of mitochondria? _______________________
__________________________________________________________.
3. CHLOROPLAST
a. Chloroplasts: plant organelles that capture solar energy and store it in the chemical bonds of
carbohydrates through the process of photosynthesis.
b. Chloroplasts are found in plant and algal cells.
c. Chloroplasts capture light energy and store this energy in carbohydrates during the light and dark
(Calvin cycle) reactions of photosynthesis.
4. MITOCHONDRIA AND CHLOROPLASTS CARRY THEIR OWN DNA
a. In mitochondria and chloroplasts, organelle DNA differs from ________________________.
b. Both organelles replicate and express ALL of the genes in ________ ___________ DNA but
their own genomes encode only some of the ____________________ they require for normal
functioning.
Page 1 of 5
Beavers
Lecture 008s2 part 2
Protein Synthesis, Genetic Code, Mutation and Gene Exp, Gen of Chloroplasts & Mito
5. Mitochondrial DNA (mtDNA)
a. Human mitochondrial DNA:
i. Size _________________. About ____________________ the size of the haploid
genome in a human gamete.
ii. Carries ____________ genes: 13 encode polypeptides for oxidative phosphorylation
apparatus, 22 tRNA genes, 2 genes for the large and small rRNA's found in
mitochondrial ribosomes.
b. Replication of mtDNA independent of “S” phase for nuclear DNA.
c. Size and gene content vary between organisms.
d. mtDNA are circular in humans and other animals, linear in most fungi and plants.
e. Single celled eukaryotes that carry a single mitochondrion known as a kinetoplast.
i. Seen in Trypanosoma (protozoan parasite responsible for African sleeping sickness –
remember in bio 6?).
1. Kinetoplast (mitochondrion) has DNA in mini and maxi circles interlocked and
the mtDNA exists in only one location.
2. Undergo RNA editing to add or delete uracils to convert pre-mRNA's into mature
mRNA's.
3. RNA editing: specific alteration of the genetic sequence carried within an RNA
molecule after transcription is complete.
6. MITOCHONDRIAL EXCEPTIONS TO THE “UNIVERSAL GENETIC CODE”
a. Mitochondrial genetic code varies in different organisms. In humans, there are 5 differences
between the universal and mitochondrial genetic codes.
b. Mitochondrial translation system differs from cytoplasmic translation system.
i. Drugs (i.e. erythromycin) inhibit bacterial translation and mitochondrial protein synthesis
but not eukaryotic cytoplasmic protein synthesis.
c. No one single mitochondrial genetic code functions for all organisms.
d. Mitochondria of higher plants use the "universal code".
7. GENETIC CODE
8. CHLOROPLAST DNA (cpDNA)
a. Chloroplast DNA carries many more genes than mtDNA.
b. Most cpDNA’s exist in a linear or branched form. Some circular.
c. Include introns.
d. Chloroplasts carry approximately 15-20 copies of their genome.
e. Special techniques have been successful in shooting DNA into cells and successfully integrating
into chloroplasts for expression.
i. Biolistic Transformation
f. Why transform chloroplasts?
9. Mitochondria and chloroplasts depend on gene products from the nucleus:
a. These organelles are semiautonomous – they require proteins and tRNA’s produced from nuclear
genes.
b. Nuclear genomes carry the genes for most of the proteins in the mitochondrial ribosome.
c. Mitochondria and chloroplasts CANNOT exist independently from the cells they inhabit.
Page 2 of 5
Beavers
Lecture 008s2 part 2
Protein Synthesis, Genetic Code, Mutation and Gene Exp, Gen of Chloroplasts & Mito
d. Evidence exists for the transfer of genes from mtDNA to nuclear DNA and cpDNA to mtDNA
demonstrating organelle-to-nucleus transfer of DNA.
e. Subsequent loss of the organellar gene made organelles unable to survive autonomously outside
of their host cell.
10. NON-MENDELIAN INHERITANCE OF CHLOROPLASTS AND MITOCHONDRIA
a. Non-Mendelian inheritance: pattern of inheritance that does not follow Mendel’s laws and does
not produce Mendelian ratios among the progeny of various crosses.
b. First described in “four-o’clocks”.
c. Reciprocal crosses demonstrated unequal contributions from paternal and maternal gametes.
d. (Oh, no!! Now what?)
e. Mutations in organelle genes produce easily detectable whole-organisms phenotypes because the
altered products disrupt the production of ENERGY.
i. Examples: unicellular organism colonies grow more slowly.
ii. Example: multicellular organism's tissues unusually weak.
iii. Mutations in cpDNA can incapacitate proteins essential for the production of chlorophyll
changing the color of the plant (and it's ability to photosynthesize!).
f. KEY QUESTION ASKED BY GENETICISTS ABOUT ORGANELLES IN DIFFERENT
SPECIES: Do progeny obtain their organelles from ____________ ________________
(biparental inheritance) or from just ________ __________________ (uniparental inheritance).
g. Enormous variation of inheritances exists amongst different _________________________.
11. Non-Mendelian Inheritance
a. RECIPROCAL CROSSES: crosses in which the traits in the males and females are reversed,
thereby controlling whether a particular trait is transmitted by the egg or the pollen.
b. Eggs from a plant with variegated leaves crossed with pollen from a green-leafed plant = ALL
VARIEGATED.
c. Eggs from a plant with green leaves crossed with pollen of variegated plant = ALL GREEN.
d. ♀ variegated leaves X ♂ green leaves = all variegated
e. ♀ green leaves X ♂ variegated leaves = all green
f. DISCOVERY:
i. Maternal Inheritance
ii. Traits produced by genomes of non-nuclear organelles.
1. The trait of variegation does not reside on DNA in the nucleus but in the genomes
of NON-NUCLEAR ORGANELLES like mitochondrion and chloroplasts.
2. Variegation trait found in cpDNA.
g. Maternal Inheritance: A type of uniparental inheritance in which all progeny have the genotype
and phenotype of the parent acting as the female.
12. CYTOPLASMIC SEGREGATION OF CHLOROPLASTS
a. Heteroplasmic: genomic makeup of a cell’s organelles characterized by a mixture of organellar
genomes.
b. Homoplasmic: genomic makeup of a cell’s organelles characterized by a single type of
organellar DNA.
c. Mutant vs. wild-type
Page 3 of 5
Beavers
Lecture 008s2 part 2
Protein Synthesis, Genetic Code, Mutation and Gene Exp, Gen of Chloroplasts & Mito
13. CROSSES USING FLOWERS FROM VARIEGATED PLANT
a. Maternal inheritance: The maternal gamete within the flower (the egg cell) determines the color
of the leaves and branches of the progeny plant.
b. The origin of the pollen is insignificant.
c. Egg cell contains many chloroplasts.
d. Pollen cell contains NO chloroplasts.
e. If the maternal branch is variegated, three types of zygotes can result, depending on whether the
egg cell contains only white, only green, or both green and white chloroplasts.
f. Variegation in a cpDNA mutation incapacitates proteins essential for photosynthesis and is
lethal following the seedling stage if all white.
14. MATERNAL INHERITANCE DEMONSTRATED IN FROGS
a. Crosses between two species of frogs (Xenopus laevis and Xenopus borealis) produce viable
offspring.
b. Researchers created unique probes for mtDNA from each species to follow the inheritance of
mtDNA in the F1 generation.
c. Each F1 hybrid retained mtDNA from only its mother.
15. UNIPARENTAL INHERITANCE
a. Organelle chromosomes are located in the cytoplasm.
b. Male and female gametes do not contribute cytoplasm equally to the zygote.
c. Organelles are generally inherited from only one parent, usually the female.
d. With nuclear genes, do both parents contribute to the zygote equally?
16. LHON: Leber Hereditary Optic Neuropathy
a. Affected individuals are usually homoplasmic.
b. Rapid loss of vision due to optic nerve death (3rd decade of life).
c. Pedigrees display clear pattern of mitochondrial (maternal) inheritance.
d. ALL offspring of mothers with mtDNA mutations demonstrate disease.
e. NO offspring of mtDNA mutation carrier fathers demonstrate disease.
f. Why does severity vary?
17. MERRF – myoclonic epilepsy with ragged red fiber disease
a. Affected individuals are usually heteroplasmic.
b. Uncontrolled jerking
c. Muscle weakness
d. Deafness, heart and kidney problems
e. Progressive dementia
f. “Ragged” staining pattern in regions of their skeletal muscles.
g. Loss of function mutation in a mtDNA tRNA genes.
18. MERFF
a. Maternal inheritance.
b. Deleterious effect on ATP production.
c. Affected individuals are heteroplasmic
d. Fraction of mutant mtDNA varies and corresponds with the severity of the disease.
e. Proportion of mutant mitochondrion and affected tissue type together determine severity.
Page 4 of 5
Beavers
Lecture 008s2 part 2
Protein Synthesis, Genetic Code, Mutation and Gene Exp, Gen of Chloroplasts & Mito
19. DISTRIBUTION OF ORGANELLES DURING MITOSIS
a. Heteroplasmic: genomic makeup of a cell’s organelles characterized by a mixture of organelle
genomes.
b. Homoplasmic: genomic makeup of a cell’s organelles characterized by a single type of organelle
DNA.
c. The larger the proportion of mutant mtDNA molecules, the greater the increase in the severity of
the expression of the disease.
d. The cytoplasm and its mitochondria have been distributed before meiosis in germ cells:
e. Only secondary oocyte and mature ovum are recipients of cytoplasm and organelles.
20. DISTRIBUTION OF MATERNAL ORGANELLES DETERMINES PHENOTYPE
i. Female parent is heteroplasmic for mitochondria.
ii. Offspring can be:
1. A. homoplasmic mutant
2. B. heteroplasmic
3. C. heteroplasmic (less severe variant)
4. D. homoplasmic wildtype
iii. Not all offspring show signs of disease
iv. Not all siblings manifest the condition with symptoms with the same severity.
b. Why?
21. Many Reasons for Uniparental Inheritance
a. Larger gamete size in female with greater cytoplasmic contribution.
b. Cell degradation of male organellar DNA.
c. Cells containing male organellar DNA distributed away from embryo.
d. Only sperm nucleus permitted to enter egg.
e. Zygote destroys paternal organelles post-fertilization.
f. OF NOTE:
g. Some species display biparental inheritance of organelles (i.e. geraniums).
h. Spontaneous somatic mutations of mtDNA can occur.
i. mtDNA mutations may play a role in aging.
22. CAN OFFSPRING HAVE THREE PARENTS?
a. Oocyte nuclear transplantation can sidestep transmission of mitochondrial disease.
b. Remove nucleus from mother’s egg.
c. Remove nucleus from donor’s egg.
d. Insert mother’s nucleus into donor egg.
e. 2009 – successful in rhesus monkeys. Success in humans 1997 and 2000?
Page 5 of 5
Beavers