Skip to main content

FROM NUCLEOTIDES TO CHROMATIN

• DNA is first coiled around a histone complex called a nucleosome. (10 nm fiber)

• Runs of nucleosomes are formed into a zig-zagging string of chromatin (30 nm fiber)

• which is then folded into loop domains (interphase chromosome 300 nm)

• finally, the metaphase chromosome. (700 nm) in diameter

Nucleosomes

• The term “nucleosome” specifically refers to the core octamer of histones plus the linker histone.

• Chromosomes are further classified based on the location of the centromere: metacentric (centromere in the middle), acrocentric (centromere toward one end), or telocentric (centromere at the end). • Kromozomlar, sentromerin konumuna göre ayrıca sınıflandırılır: metasentrik (sentromer ortada), akrosentrik (bir uca doğru sentromer) veya telosentrik (sonda sentromer).

• Each chromosome must contain a centromere, one or more origins of replication, and a telomere at each end.• Her kromozom bir sentromer, bir veya daha fazla replikasyon kaynağı ve her uçta bir telomer içermelidir.

• Telomeres are specialized structures that cap the end of chromosomes and prevent them from being joined to each other.• Telomerler, kromozomların uçlarını kapatan ve birbirlerine bağlanmalarını engelleyen özel yapılardır.

ALTERNATIVE DNA BASED GENOMES

Bacterial Genome

• Prokaryotes do not have a nucleus.

• A considerable number of nonessential proteins, called histone-like proteins or nucleoid-associated proteins, are thought to be involved in DNA compaction and genome organization.

Plasmids

• Plasmids are small, double-stranded circular or linear DNA molecules carried by bacteria, some fungi, and some higher plants.

• They are extrachromosomal (meaning separate from the host cell chromosome), independent, and self-replicating.

• Plasmids are important for two main reasons:

• they are carriers of resistance to antibiotics,

• and they provide convenient vehicles for recombinant DNA technology.

Bacteriophages

• The motivation for most of the early studies on viruses centered on their pathogenicity, but they have also proved extremely useful systems for analysis of fundamental principles of molecular biology.

• Before the advent of gene cloning technologies, viruses provided a readily available source of pure DNA for studies of genomic expression, function, and replication.

Mammalian DNA viruses

The most important model systems for understanding molecular and genetic characteristics of eukaryotes.

ORGANELLE GENOMES

Chloroplast DNA (cpDNA)

• Chloroplasts are found in higher plants, some protozoans, and algae.

• The cpDNA encodes enzymes involved in photosynthesis.

Mitochondrial DNA (mtDNA)

• Mitochondria are found in plants, animals, fungi, and aerobic protists.

• The mtDNA encodes essential enzymes involved in ATP production in respiratory process.

RNA GENOMES

Eukaryotic RNA Viruses

• They infect many different hosts, including plants and animals.

• Medically, they are an extremely important group, with many significant human or veterinary pathogens

• They come in a variety of sizes and shapes, with enveloped or nonenveloped capsids (external protein coat).

• The envelope is a layer of lipid and protein surrounding the capsid.

• Typical RNA viruses replicate without forming DNA intermediates.

• Retroviruses, replicate RNAàDNAàRNA by revers transcription.

Retroviruses

• Retroviruses are also called “RNA tumor viruses” because many members play a role in cancer.

• Retroviruses have single-stranded RNA genomes that replicate through a DNA intermediate by reverse transcription.

• Consequently, retroviruses currently are impossible to get rid of completely after infection and integration.

• Retroviruses are important vectors for gene therapy.

Viroids

• Viroids are “subviral” pathogens that cause infectious disease in higher plants.

• The viroid genome consists of a single, very small, circular molecule of RNA, ranging in size from 250 to 400 nt. Unlike viral RNAs, viroid RNAs do not encode any proteins and they are not protected by a protein coat.

Other Subviral Pathogens

• Include satellite RNAs and virusoids.

• Viroids replicate autonomously by using host-encoded RNA polymerase.

• In contrast, satellite RNAs multiply only in the presence of a helper virus that provides the appropriate RNA-dependent RNA polymerase.

 


Popular posts from this blog

FARMAKOGENOMIK

¨ Farmakogenomik terimi, belirli aday genlerde bulunan dizi varyasyonunun, bireylerin ilaca karşı cevabını nasıl etkilediğini inceleyen farmakogenetik ile değiştirilerek kullanılabilir. Kişiye özel tedavi; her bir hastaya özel ilaç oluşturulması yerine; kişilerin belli bir hastalığa duyarlılığı ya da spesifik tedaviye yanıtlarına göre küçük populasyonlara ayrılıp bu populasyonlara özel ilaç oluşturulmasıdır . FDA-onaylı ilaçların %10’u farmakogenomik bilgileri içeren etiket bulundurmaktadır. Kişisel Tıp ve Hatalık Tanısı ¨ Tanı Testleri ¤ Semptomatik hastalarda, şüpheli genetik bozukluğa bağlı gen varyasyonlarının var yok analizleri ¨ Tahmini Testleri ¤ Bilinen hastalığı içeren aile öyküsü bulunan hastalarda gen mutasyon saptanması (Huntingon Hastalığı veya BRCA bağlı meme kanseri) ¨ Taşıyıcı Testleri ¤ Yavrulara geçebilen, hastalığa neden olan mutasyonları taşıyan hastaların belirlenmesine yardımcı olur (Tay-Sachs ve kistik fibrozis) ¨ Prenatal Testler ¤ Fetusta...
Read more

MUTATIONS AND DNA REPAIR MECHANISIMS

Types Of Mutations • Spontaneous mutations: occur because of natural processes in cells, for example DNA replication errors. • Induced mutations: occur because of interaction of DNA with an outside agent or mutagen that causes DNA damage. the importance of mutations  genetic variation  deleterious or advantageous  mutations in germ cells can lead to heritable genetic disorders. mutations in somatic cells may lead to acquired diseases such as cancer or neurodegenerative disorders.  tools for molecular biologists in characterizing the genes.  • Mutations that alter a single nucleotide pair are called point mutations.  Other Kinds of Mutations  expansions of trinucleotide repeats,  extensive insertions and deletions major chromosomal rearrangements • Transition mutations replace one pyrimidine base with another, or one purine base with another.  • Transversion mutations replace a pyrimidine with a purine or vice versa. Sickle cell anemia mutatio...
Read more

CONVENTIONAL METHODS IN MOLECULAR BIOLOGY

  Comparison of conventional and modern techniques  • In conventional techniques, isolation and manipulation of DNA or RNA is not applied.  • Experiments are set based on phenotypic characters and the results are expressed based on observations or quantitative measurements.  • The basic materials of modern biotechnology are nucleic acids (NA) and proteins (P).  • NA and P are isolated from tissue, purified and subjected to certain processes.  • NAs are amplified in bacteria or by polymerase chain reaction (PCR), cut with restriction enzymes and hybridized with a different NA, If necessary, or run on an Agarose Gel Electrophoresis, stained and visualized.  • Likewise, proteins are purified, run on an SDS-PAGE gel, stained/immunoblotted and visualized.  Proof of transforming factor   In vivo Experiment  • In 1928, Frederick Griffith described a transforming principle that transmitted the ability of bacteria to cause pneumonia in mice. “tra...
Read more