Keywords for Genetics, 2020. Important: these definitions are for the „A” part of the exam. This is basic knowledge, not enough for passing the exam. Might change a little during the semester as I try to correct existing mistakes. 1. The nature of genetic material. DNA and its structure. Higher organization of DNA. RNA in inheritance. Genetic material – chemical substances which carry inheritable information. In living organisms this is basically the double stranded DNA. In non-living it can be DNA, RNA also (for example some viruses) or proteins (e.i. prions) Genome – the whole genetic information of an organism. For example in eukaryotes it can comprise of chromosomal and extrachromosomal genetic material (e.g. mitochondrial and plastid DNA). Transformation – an event in which a cell (e.g.: prokaryotes, yeasts or even human cells) acquires new features through the uptake of new genetic material cells transform into something new. Typical example: non-virulent bacteria become virulent by up taking DNA that carries virulence information. Prions/prion proteins – normally a protein associated with cell membrane, which is when functioning normally is needed for healthy cells. BUT when its structure changes, this leads to abnormal function and causes prion diseases. It can be regarded as genetic information, because this information is passable to other proteins and organisms. The defected proteins contain beta sheets, not alpha helixes. DNA – deoxyribonucleic acid. DNA is the genetic information carrier chemical substance in living organisms. It is composed of deoxyriboses, phosphates and organic nucleobases. Its basic form is the B form, where there are two strands running in an anti-parallel way. DNA is a macromolecule, a polymer and its subunits are called nucleotides. Nucleoside – a component of nucleic acids. It only contains a pentose and a nucleobase. Nucleotide – can be subunit of nucleic acids. A nucleotide is composed of nucleoside and phosphate(s). E.g.: AMP, ADP, dTTP, etc.). Nucleobases – are nitrogen containing, aromatic parts of the nucleosides/nucleotides/nucleic acids. In nucleic acids they basically determine the specificity. They can be subgrouped to purin (adenine, guanine) and pirimidine (thymine, cytosine and uracil) types. Phosphodiester bond – is a covalent bond between nucleotides in one strand, for example in DNA. In case of DNA, the participants in forming the bond are the 5’ phosphate of a nucleotide and the 3’ OH group of the adjacent nucleotide. Complementarity – in DNA (and sometimes in RNA) hydrogen bonds form between nucleotides that are „in front of each other”. These bonds form by specific pairing of nucleobases: adenin with thymine and cytosine with guanine in case of DNA. Can be seen in case of RNAs, also. DNA denaturation – in case of for example of high temperature the two strands of double stranded DNA becomes separated, because the high temperature diminishes the hydrogen bonds. Melting temperature (Tm) – the temperature where 50% of the given DNA becomes separated. GC ratio – it shows how much guanine/cytosine can be found in given DNA (~in genome). This primarily defines the melting temperature, which is a characteristic of a living organism. DNA hybridization – processes and procedure/techniques in which separated DNA strands try top air up with DNA (or RNA strands). This can be used for example for evolutionary studies or in forensic science. Techniques like microarray and southern/northern blots are based on hybridization. Superhelicity of the DNA – the phenomenon, when dsDNA twists further more around itself. This can happen in passive way or an active way, the latter with the help of topoisomerases. This feature of DNA structure helps to make the DNA more compact, so it can fit in cells. Topoisomerases –enzymes that can change the topology of DNA by cutting and reconnecting the DNA strands. They have crucial roles in forming and removing DNA superhelicity, and stopping the torsional tension. Some topoisomerases cut only one strand, others cut both strands of the dsDNA. Nucleosome – The basic unit of chromatin, that is composed of DNA and central histone proteins. DNA twists around the histone octamer protein complex (H2A, H2B, H3 and H4 – 2 times) about 2x. The loose structure of nucleosomes gives the so called beads-on-string structure. These are found in eukaryotes. Chromatin – chromosomal DNA of the nucleus + RNA around the DNA and all the protein that attach to DNA is called chromatin. Microscopically (and functionally) there are 2 types: euchromatin and heterochromatin (facultative and constitutive). Euchromatin – the loose part of chromatin. Active genes are found here, and transcription (RNA synthesis) can happen, mostly with the help of transcription factors. Free DNA and beads-on-string structure form the euchromatin. On microscope, it is the lighter part region of the nucleus. It can transform into facultative heterochromatin. Heterochromatin – the compact region of chromatin. Here there is no transcription, because genes cannot be activated, or there are no genes here. This denser structure is formed by the further compaction of the „beads-on-the string” into the 30 nm and even more into the 300 nm structure. With microscope it can be visualized as the darker part of the nucleus. Two forms: a. facultative heterochromatin – it can change to euchromatin if needed and b. constitutive heterochromatin – since there ain’t no genes here it, always stays heterochromatic. Metaphase chromosome – a chromosome that is in the most compact form, it can only be found in cells that are in metaphase of mitosis or meiosis. It consists of two sister-chromatids which are only attached at the centromer region by cohesin proteins. After sister-chromatid separation in anaphase (mitosis) or anaphase II (meiosis II), during the formation of the daughter nuclei these sister- chroamtids will be named chromosomes again. Centromere – part of the linear chromosome, where kinetochore complex can be found. The region where during metaphase, the sister-chromatids are attached to each other in case of metaphase chromosomes. The kinetochore complex binds microtubules during mitosis and meiosis and is essential for sister-chromatid or chromosome separation. The centromer is usually in constitutive heterochromatin state; also there are no coding regions here. Telomere – the end region of the linear chromosome. It is constitutive heterochromatin, so it doesn’t contain any genes. It is composed of DNA, histones, but also specific proteins such as Shelterin and Sir proteins. The DNA here contains hundreds of tandem repeats, which in, for example „average” somatic cells after every DNA replication and cell division gets shorter and shorter. In some cells there is an enzyme called telomerase which can recreate telomere (for example in embryonic stem cells, in gamete producing germ cells, and unfortunately in cancer cells). Replicative senescence – most mammalian cells, including the majority of human cells has this property. These cells have limited number of possible cell divisions to carry out. This is due to that the telomere gets shorter and shorter every time after each DNA replication and thus after mitotic cell divisions. After about 50-60 replication and cell divisions, the cell cannot make more divisions and they will stay in senescence or in some cases they do apoptosis. Telomerase – a specific enzyme that can restore the length of telomeres. It has protein and RNA part. In healthy humans it only works in stem cells and gamete producing germ cells. In case of cancer, usually it is reactivated in the tumor cells, thus providing immortality for the tumor cells. Karyotype – the total chromosome content of a cell/organism. We can artificially differ microscopic and electrophoretic karyotypes. Microscopic karyotype (~karyogram) – usually it means the ordered profile of metaphase chromosomes. Chromosomes are ordered by size in a decreasing manner, and giving them numbers, except for the sex chromosomes, which are shown in the last position in a karyogram. Ploidity – shows that how many complete sets of homologous chromosomes a cell/organism carries. Usually it is designated with „n”. For examples fission yeast is monoploid: „1n”; or humans are diploid so they are „2n”s. Euploid – those cells that carry the integer multiple of the complete chromosome set: haploid/monoploid (1n), diploid (2n), triploid (3n), etc. Aneuploid – those type of cells that also carry non-complete chromosome set(s) in addition to the complete sets. We can subgroup them to hyperploids (carry more) and hypoploids (carry less). Autoploids – carry 2 or more copies of the same monoploid chromosome set. Allodiploid=amphihaploid – carry 2 different monoploid sets of chromosomes, that have different origin (2 x 1 n). Usually sterile – cannot produce gametes. Allotetretrapoid=amphidiploid – carry 2 different diploid sets of chromosomes, that have different origin (2 x 2 n). Usually capable of reproduction. Hypoploid – it carries 1 or more complete sets of chromosomes and 1 or more incomplete sets. E.g.: nullisomy; monosomy (in human - 45, X=Turner syndrome). Hyperploid – it carries 1 or more complete sets of chromosomes and 1 or more extra chromosomes. E.g.: trisomy (47, +21 = Down syndrome). Nondisjunction – chromosome pairs (in meiosis I), and sister-chromatids (in mitosis, and meiosis II) are wrongly or not separated. This leads to unequal chromosome content in daughter cells. These abnormal chromosome contents can lead to death of