Главная Случайная страница


Полезное:

Как сделать разговор полезным и приятным Как сделать объемную звезду своими руками Как сделать то, что делать не хочется? Как сделать погремушку Как сделать так чтобы женщины сами знакомились с вами Как сделать идею коммерческой Как сделать хорошую растяжку ног? Как сделать наш разум здоровым? Как сделать, чтобы люди обманывали меньше Вопрос 4. Как сделать так, чтобы вас уважали и ценили? Как сделать лучше себе и другим людям Как сделать свидание интересным?


Категории:

АрхитектураАстрономияБиологияГеографияГеологияИнформатикаИскусствоИсторияКулинарияКультураМаркетингМатематикаМедицинаМенеджментОхрана трудаПравоПроизводствоПсихологияРелигияСоциологияСпортТехникаФизикаФилософияХимияЭкологияЭкономикаЭлектроника






Lecture 1.4 Сytoplasmic inheritance





Intracellular mechanisms of multicellular organisms’ genetic processes research. Nucleus and cytoplasm role in heredity relationship

Plan

1. Cytoplasmic heredity research

2. Cytoplasmic carriers of genetic information

3. Plastid’s heredity. Cytoplasmic male sterility

4. Chromosomal genes and plasmogenes role in organism’s characteristics formation

5. Epigenetic inheritance

 

1. Cytoplasmic heredity research

There are many indications that cytoplasmic elements do play important roles in cellular development and heredity.

Elements which have all properties of genes exist in the cytoplasm. Cytoplasm contain an auxiliary set of genes which are separated from the main nuclear hereditary material, they are possibly relics of some ancient system of cellular organization which has been almost abandoned (ликвидировать) in the course of evolution.

Already in the first years of genetics as a science formation the facts were known, which show that certain traits inheritance is associated with non-chromosomal cell components and does not obey the laws of Mendel. In 1908–1909 K. Correns and E. Baur independently described variegation (variegated leaves) in four o’clock plants and snapdragons, which is inherited through the cytoplasm.

In 1937, French geneticist Lerite discovered mutation of flies Drosophila melanogaster, causing their death in an atmosphere of carbon dioxide - CO2. Mutation was not inherited by Mendel, but by peculiar way: through the cytoplasm and not only through the maternal line. In a small percentage of cases there was a regular transfer of sensitivity to CO2 through males. Sensitivity can be transmitted by injection of hemolymph (it is a fluid in the circulatory system of arthropods, analogous to the blood in vertebrates). In these cases, a sign inheritance was unstable. Sensitivity to CO2 was associated with reproduction in flies’ cells of RNA -containing virus. Oogonia of females contain 10-40 viral particles and mature oocytes – up to 10 million particles. Virus «sigma» is typical facultative element, and mutation of viral and flies’ genomes lead to complex behaviors of this system. Increased temperature blocks the replication of virus particles. If females and males during gametogenesis will be for a few days at a temperature of 30 °C, then the offspring of such heat-treated flies will be free from virus and resistant to CO2.

If Euglena (lat. Euglena viridis) loses plastids it cannot restore them, despite the preserved nucleus. Most species of Euglena have about 100 photosynthesizing chloroplasts within the cell, which enable them to feed by autotrophy, like plants. In the darkness they can also take nutriments heterotrophically, like animals, plastids do not multiplied, although Euglena cells continue division. In a few generations individuals without chloroplasts appear, their offspring also haven’t chloroplasts.

There are plasmids in bacteria cytoplasm circular DNA fragments, which are located separately from the main DNA molecule of bacterial cell. In some eukaryotic cells, such as yeast, additional DNA molecules are also found, which can ensure the stability of yeast against toxic substances.

These are examples of cytoplasmic inheritance, which for a long time have been considered as some departure from the laws of Mendel.

A characteristic feature of the cytoplasmic heredity is inheritance from a mother. At gametes fusion only the sperm nucleus with genetic material gets into the egg. Zygote receives cytoplasm and its contents only from the mother.

 

2. Cytoplasmic carriers of genetic information

Genetic material of chromosomes (genome) corresponds to the plasmon, which includes all cytoplasmic genetic material. Plasmogenes or extra chromosomal heredity material carriers are located in cytoplasm compartments. They determine the development of some cell signs, capable of doubling, are distributed between daughter cells during mother cell division.

Types of non-nuclear cell hereditary constituents:

1. plasmids

2. mitochondria

3. plastids

4. centrosomes or cellular center

5. small cytoplasmic particles such as ribosomes

6. surface structures, including basal bodies (kinetosomes).

Centrosome (Greek. σῶμα – body) or cell center is non-membrane organelle that serves as the main microtubule organizing center (MTOC) of eukaryotic cell as well as a regulator of cell-cycle progression. It was discovered by Edouard Van Beneden in 1883 and was described and named in 1888 by Theodor Boveri (“special organ of cell division”). Centrosome in many living organisms (animals and some protozoa) contains a pair of centrioles, cylindrical structures at right angles to each other. Each centriole (length 0.2-0.8 microns) is formed by nine triplets of microtubules arranged in a circle.

In the interphase of the cell cycle centrosomes are associated with the nuclear membrane. In prophase of mitosis the nuclear membrane breaks down, centrosome divides. Centrioles apart to the poles, defining the axis of cell division spindle. Microtubules growing from child centrosomes, fastened the other end to the kinetochores at chromosome centromeres, forming the division spindle.

In addition to participation in nucleus division, centrosome plays an important role in the formation of flagella and cilia ( жгутиков и ресничек ). Centrioles are located in centrosome, there are an organizing centers for flagella microtubules.

A basal body is also called a basal granule or kinetosome ( Greek. kinetós – moving and soma – body ). This is an organelle originated from a centriole. They are structurally the same, each containing 9 microtubule triplet of helicoidal configuration forming a hollow cylinder coated by membrane. In addition to proteins, carbohydrates and lipids, kinetosome contains DNA and RNA and is capable of self-protein biosynthesis and self-reproduction.

Basal body (kinetosome) is specifically the bases for cilia and flagella that extend out of the cell, deep in the thick of ectoplasm. Fibrils are a direct continuation of flagella peripheral fibrils. Flagella are basically attached to the cell membrane from a basal granule.

It is possible that the cytoplasmic heredity is also based on long-lived mRNA molecules or on selective RNA transcription from the maternal chromosome genes only.

Two forms of cytoplasmic inheritance are the best studied: plastid inheritance and cytoplasmic male sterility.

Plastids are major organelles found in eukaryotic cells of plants, algae and some unicellular organisms. They are the site of manufacture and storage of important chemical compounds used by the cell. Plastids often contain pigments used in photosynthesis, and the types of pigments present can change or determine the cell's color. They are coated by two membranes and possess a double-stranded DNA molecule, which is circular, like that of prokaryotes.

In plants, plastids may differentiate into several forms, depending upon which function they play in the cell. Undifferentiated plastids (proplastids) may develop into any of the following variants:

· Chloroplasts green plastids: for photosynthesis;

· Chromoplasts/coloured plastids: for pigment synthesis and storage

· Gerontoplasts: control the dismantling of the photosynthetic apparatus during senescence

· Leucoplasts/colourless plastids: for monoterpene synthesis; leucoplasts sometimes differentiate into more specialized plastids:

· Amyloplasts: for starch storage and detecting gravity

· Elaioplasts: for storing fats

· Proteinoplast/aleuronoplasts: for storing and modifying proteins

A mitochondrion contains outer and inner membranes composed of phospholipid bilayers and proteins. The two membranes have different properties. Because of this double-membraned organization, mitochondrion has five distinct parts:

1. the outer mitochondrial membrane,

2. the intermembrane space (the space between the outer and inner membranes),

3. the inner mitochondrial membrane,

4. the cristae space (formed by infoldings of the inner membrane), and

5. the matrix (space within the inner membrane).

The human mitochondrial genome is a circular DNA molecule of about 16 kilobases. It encodes 37 genes: 13 for subunits of respiratory complexes I, III, IV and V, 22 for mitochondrial tRNA (for the 20 standard amino acids, plus an extra gene for leucine and serine), and 2 for rRNA. One mitochondrion can contain two to ten copies of its DNA.

As in prokaryotes, there is a very high proportion of coding DNA and an absence of repeats. Mitochondrial genes are transcribed as multigenic transcripts, which are cleaved and polyadenylated to yield mature mRNAs.

Not all proteins necessary for mitochondrial function are encoded by the mitochondrial genome; most are coded by genes in the cell nucleus and the corresponding proteins are imported into the mitochondrion.

The exact number of genes encoded by the nucleus and the mitochondrial genome differs between species. In general, mitochondrial genomes are circular. it lacks introns, as is the case in the human mitochondrial genome; however, introns have been observed in some eukaryotic mitochondrial DNA, such as that of yeast and protists, including Dictyostelium discoideum

Diagram of a mitochondrion Two mitochondria from mammalian

lung tissue displaying their matrix

and membranes as shown by

electron microscopy

3. Plastid’s heredity. Cytoplasmic male sterility

In many cases, changes in plastids structure and function are associated with mutations in chromosomal genes. In maize, barley and other crops numerous chlorophyll mutation are studied. They inherit by the rules of Mendel. Often, however, the inheritance of such changes is not subject to the laws of the Mendel, and it may only be explained on the basis of cytoplasmic inheritance.

Four o’clock plants ( Mirábilis jalápa) may have variegated leaves. On one plant there are as completely green branches as branches with leaves with green parts and parts with clear stripes and spots. The flowers on the green branches of the variegated plants, no matter what pollen they are pollinated, provide seeds that always grow as normal green plants. Seeds from the branches without green color give colorless sprouts without chlorophyll. Seeds from the variegated shoots give offspring mixed in various ratios, consisting of green, variegated and colorless plants. A similar phenomenon was observed in variegated plants of snapdragons (Antirrhínum), pelargonium (Pelargonium), plantain (Plantágo, подорожник), evening primrose (Oenothera biennis, энотера, ослинник, примула вечерняя).

 

 

 

 

These facts can be explained by assuming that the variegated plants have two types of plastids: normal with chlorophyll and abnormal, those are not able to form chlorophyll. During the multiplication of the normal plastids normal offspring forms, but from abnormal – abnormal (white) plastids. Variegated mother plant produces three types of eggs: with green, colorless and mixed plastids. Since sperm cells do not contain plastids, the number of different progeny plants is determined by random plastids distribution during macrosporogenesis. After green maternal plant pollination only normal offspring with green leaves appears, after abnormal/colorless – just abnormal phenotype, regardless of the paternal form.

Cytoplasmic male sterility is total or partial male sterility associated with plant biology as the result of specific nuclear and mitochondrial interactions. Male sterility is the failure of plants to produce functional anthers (пыльники), pollen, or male gametes, the cause of which is the presence of a particular mutation in mitohondrione, i.e. in mitochondria genome. Plant fertility is restored completely or partially in the presence of a dominant allele of the nuclear fertility restorer gene. First this phenomenon is described by Marcus M. Rhodes in maize, now it is described in petunias, cabbage, sunflower and other plants. Cytoplasmic male sterility is characterized by so-called maternal inheritance.

 

4. Chromosomal genes and plasmogenes role in organism’s characteristics formation

Cell is a single integrated system, which determines traits transmission and reproduction in the offspring as the result of nuclear components (genes of chromosomes) interaction with the cytoplasm.

Most of the mitochondrial proteins encoded by the nuclear genes inherit according Mendel rules, other proteins encoded by mitochondrial DNA, which are transmitted only through the maternal line. Genes of cellular respiration enzymes found in mitochondria, as well as genes of resistance to several adverse effects.

Photosynthesis is associated with cytoplasmic structures of the cell –plastids and contained therein pigment chlorophyll. Plastids formation and function are caused by hereditary factors and by influence of external conditions (mainly light, in darkness the chlorophyll in the plastids is not form). During division of the cell containing abnormal plastids daughter cells form with the same plastids. This sign is transmitted only through the maternal line, and, therefore, it is not associated with the chromosomes, but with cytoplasm. Thus, the most important property of the cell – its ability to photosynthesis – is determined by the interaction of chromosomal genes, cytoplasmic structural elements, and the external environment.

 

5. Epigenetic inheritance

Epigenetics is the study of epigenetic inheritance patterns – the inheritance of the active or inactive state of individual genes (or gene groups) without a change or loss of the encoded in them genetic information.

Epigenetic changes are stored in a number of cell divisions, and can be transmitted to the next generation during meiosis. However, they do not cause any change in the DNA sequence and lead to differential gene expression.

The phenotype of the cell or organism as a whole depends on which genes are transcribed; inheritance of transcriptional genes status can lead to epigenetic effects. There are several levels of gene expression regulation, the first is remodeling of chromatin – DNA and associated proteins – histones – complex. Chromatin remodeling may be initiated by histone amino acids post-translational modification, for example, phosphorylation, ubiquitination, acetylation, deacetylation, methylation, sumoylation, as well as chemical modification of nitrogenous bases, for example, methylation of cytosine in DNA. In most cases, histone methylation or deacetylation leads to the suppression of gene activity, especially the methylation of its promoter regions, and demethylation – to it activation.

Сумоилирование (sumoylation) [англ. s(mall) u(biquitin-related) mo(difier) – малый убиквитин-родственный модификатор] – посттрансляционная модификация белка, заключающаяся в ковалентном связывании эпсилон-аминогруппы лизина, расположенной на С-конце полипептида, с белком SUMO, представляющим из себя компонент убиквитиновой системы.

 

Heritable information transfer or change during meiosis or mitosis, is not based on the DNA sequence can also occur with the prion proteins, and proteins.

Prions (from the English Proteinaceous infectious particles – infectious protein particles) – a new class of infectious agents, pure protein containing, no nucleic acids, causing severe diseases of central nervous system in humans and some higher animals (so-called "slow infection").

Prion protein with anomalous three-dimensional structure can directly catalyze the structural transformation of the normal cellular homologous protein to a similar (prion) protein, connecting the target protein and changing its conformation. Typically, prion protein state is characterized by the convertion of protein α-helix into β-layer. Prions are the only known infectious agents that multiple without nucleic acids participation. They carry out the only known way of information transfer from protein to protein.

 

Same Genes but a Different Kink in the Tail

 

Geneticist Emma Whitelaw (University of Sydney, Australia) studies phenomena in mice similar to those seen in human monozygotic twins, whereby genetically identical individuals can look or behave very differently. In a litter of mice that had all stably inherited a transgene at a specific locus, some mice expressed the transgene, but others didn't. This variable gene expressivity in genetically identical animals suggested that some kind of epigenetic mark had occurred differentially between individuals by chance.

For all these mice, epigenetic marks responsible for variable expressivity are inherited between generations. There are mice with kinky tails; the degree of kinkiness varies among genetically identical littermates.


 

Date: 2015-09-02; view: 489; Нарушение авторских прав; Помощь в написании работы --> СЮДА...



mydocx.ru - 2015-2024 year. (0.006 sec.) Все материалы представленные на сайте исключительно с целью ознакомления читателями и не преследуют коммерческих целей или нарушение авторских прав - Пожаловаться на публикацию