0:00:00.680,0:00:06.680 Hello. In this lecture, we will focus on the  processes that occur during gene expression. 0:00:06.680,0:00:12.480 The lecture is part of module 1, Animal  Genetics. The creation of this presentation 0:00:12.480,0:00:19.840 was supported by the ERASMUS + KA2 grant  within the project ISAGREED, Innovation 0:00:19.840,0:00:25.520 of content and structure of study programs in  the field of management of animal genetic and 0:00:25.520,0:00:33.720 food resources using digitalization. Genes contain biological information, 0:00:33.720,0:00:40.880 but they are not capable of implementing this  information in a cell themselves. Its utilization 0:00:40.880,0:00:46.920 requires coordinated activity of enzymes and  other types of proteins that are involved 0:00:46.920,0:00:54.640 in a series of events forming gene expression. Gene expression is usually viewed as a two-phase 0:00:54.640,0:01:01.320 process that involves transcription of genetic  information from a DNA sequence into its copy 0:01:01.320,0:01:08.480 in an RNA sequence. The second process is  translation, when the genetic information is 0:01:08.480,0:01:15.040 translated from the RNA sequence into the  sequence of amino acids, that is, into a 0:01:15.040,0:01:22.840 protein. All of these processes are based on the  structural properties of nucleic acids - namely, 0:01:22.840,0:01:29.840 base complementarity and antiparallelism  in the double-stranded structures of DNA. 0:01:31.680,0:01:38.240 The function of DNA is collectively described  by the so-called Central dogma of molecular 0:01:38.240,0:01:45.160 biology. It describes the flow of genetic  information between biological molecules 0:01:45.160,0:01:50.440 (i.e., nucleic acids and proteins) and is  based on the knowledge of the structure of 0:01:50.440,0:01:58.760 DNA as described by its discoverers Watson and  Crick. Common transfers include DNA replication, 0:01:58.760,0:02:06.360 RNA synthesis based on DNA (transcription), and  the transfer of genetic information from RNA to 0:02:06.360,0:02:15.600 protein (translation). Only specific groups of  RNA viruses have the ability to replicate RNA 0:02:15.600,0:02:24.040 and create DNA based on RNA, named as reverse  transcription. However, it is not possible 0:02:24.040,0:02:33.680 to transfer genetic information from a protein  back to a nucleic acid under any circumstances. 0:02:33.680,0:02:38.960 Gene expression is a process in which  information from a gene is used to synthesize 0:02:38.960,0:02:46.440 a functional gene product, i.e., a protein  or non-coding RNA with a specific function, 0:02:46.440,0:02:52.440 and ultimately influences the phenotype. The  expression of genetic information is a process 0:02:52.440,0:02:58.200 that includes two steps: transcription  and translation. These processes produce 0:02:58.200,0:03:06.320 proteins that are the basis of correct cell  and organism composition and function. 0:03:06.320,0:03:12.440 Later it was found that the process of gene  expression does not only involve the formation 0:03:12.440,0:03:21.640 of proteins. Only a small portion of cellular  RNA, usually no more than 4% of total RNA, 0:03:21.640,0:03:28.680 is composed of messenger RNA. Most of the RNA  produced in a cell is used to support the process 0:03:28.680,0:03:35.160 of translation or regulate gene expression,  meaning they are RNA molecules that will not 0:03:35.160,0:03:44.560 be translated into proteins. They thus play a  direct role in the cell as RNA itself - small 0:03:44.560,0:03:53.200 nuclear RNA (snRNA), small nucleolar RNA (snoRNA),  small cytoplasmic RNA (scRNA), microRNA (miRNA), 0:03:53.200,0:04:02.520 and possibly small interfering RNA (siRNA). The expression scheme shows in detail most of 0:04:02.520,0:04:08.400 the processes related to the expression of the  structural gene, i.e., the gene that codes for 0:04:08.400,0:04:16.440 a protein. In addition to the two basic processes  of transcription and translation, it also includes 0:04:16.440,0:04:23.840 post-transcriptional RNA modifications and  post-translational protein modifications. 0:04:23.840,0:04:29.680 These are a series of regulatory steps that can  influence the final form of the protein coded 0:04:29.680,0:04:38.440 in the DNA sequence referred to as a gene. There  is also an influence of the environment in which 0:04:38.440,0:04:48.840 the cell or organism is located, which can also  modify the outcome of a given expression step. 0:04:48.840,0:04:55.480 Perhaps the most important phase of transcription  is the first phase, called initiation of 0:04:55.480,0:05:02.720 transcription. Not all genes are constantly  transcribed. On the contrary, there are mechanisms 0:05:02.720,0:05:10.280 that ensure gene activation as needed. It must  be said that most genes in a cell are silenced at 0:05:10.280,0:05:18.400 any given moment. However, how does RNA polymerase  know where the gene is in DNA located and that it 0:05:18.400,0:05:24.760 should transcribe this gene? The main mechanism  for initiating gene expression is the function 0:05:24.760,0:05:31.600 of the gene promoter, which is a DNA sequence  that initiates the transcription of a specific 0:05:31.600,0:05:38.560 gene by binding to RNA polymerase and other  components of the transcription apparatus, 0:05:38.560,0:05:48.040 called transcription factors. RNA polymerases are  enzymes that perform transcription itself - RNA 0:05:48.040,0:05:55.920 polymerization based on a template strand in  DNA. In eukaryotes, there are three basic types 0:05:55.920,0:06:06.560 of RNA polymerases (I - III), each with typical  promoters. The core promoter of RNA polymerase II 0:06:06.560,0:06:16.160 in eukaryotes consists of two main segments.  The first is in the region -25, TATA box, 0:06:16.160,0:06:23.120 which has a conserved sequence 5'-TATAWAAR-3'.  The second part of the promoter core is the 0:06:23.120,0:06:34.920 initiator sequence (Inr), which, for example,  is located around nucleotide +1 in mammals. 0:06:34.920,0:06:40.280 All genes undergo the first phase of  gene expression, called transcription, 0:06:40.280,0:06:48.760 which results in the synthesis of an RNA molecule.  Transcription is a simple copying reaction. RNA is 0:06:48.760,0:06:56.880 a polynucleotide, chemically differing from DNA  only in that RNA has the sugar ribose instead of 0:06:56.880,0:07:04.440 2'-deoxyribose, and that thymine is replaced  by the base uracil (U), which, like thymine, 0:07:04.440,0:07:12.000 pairs with adenine. During the transcription  of a gene, one strand of the double helix DNA 0:07:12.000,0:07:18.760 serves as a template for the synthesis  of an RNA molecule, and the sequence of 0:07:18.760,0:07:27.400 nucleotides is based on complementarity,  i.e. standard base pairing rules. 0:07:27.400,0:07:34.680 In the diagram, we can see that DNA is a double  helix and genetic information is only encoded in 0:07:34.680,0:07:42.480 one strand, which is referred to as the coding or  positive strand. Here, the information about the 0:07:42.480,0:07:50.160 amino acid sequence in the encoded protein is  stored. However, due to base complementarity, 0:07:50.160,0:07:57.240 the second strand, the so-called negative strand,  often referred to as the anti-coding strand, 0:07:57.240,0:08:04.920 serves as the template. The enzyme RNA  polymerase moves along this strand and, 0:08:04.920,0:08:10.160 based on base complementarity,  polymerizes the growing RNA chain. 0:08:10.160,0:08:17.640 The resulting primary RNA transcript carries  the same information, i.e. the same sequence, 0:08:17.640,0:08:24.440 as the coding positive strand, with the same  orientation. The ends that are invariant within 0:08:24.440,0:08:33.480 the DNA strand are designated as 5' and 3'. The primary transcript must undergo further 0:08:33.480,0:08:40.720 processing. RNA processing involves capping,  splicing, and polyadenylation. Capping and 0:08:40.720,0:08:47.720 polyadenylation serve to protect the RNA from  degradation in the cell. Splicing specifically 0:08:47.720,0:08:55.280 removes non-coding internal parts of the gene,  known as introns. As an example of alternative 0:08:55.280,0:09:02.960 splicing, the splicing of pre-mRNA transcript of  the alpha-tropomyosin gene in rats in different 0:09:02.960,0:09:10.680 types of cells is shown in the diagram. One  gene can produce 9 different final transcripts, 0:09:10.680,0:09:17.560 with nine slightly different but similar  proteins. Light green frames represent introns; 0:09:17.560,0:09:23.000 other colored boxes represent exons.  Polyadenylation signals are marked 0:09:23.000,0:09:32.520 with the letter A. Dashed lines indicate the  regions that have been removed by splicing. 0:09:32.520,0:09:39.680 For some genes, the RNA transcript itself is the  final product of gene expression. In structural 0:09:39.680,0:09:45.600 genes, the transcript is a short-term message  that controls the second phase of gene expression, 0:09:45.600,0:09:52.600 called translation. It involves translating the  genetic information (the nucleotide sequence 0:09:52.600,0:09:59.160 encoding the amino acids of a peptide) into  the primary structure of a polypeptide (i.e. 0:09:59.160,0:10:06.040 the sequence of amino acids). Protein is another  type of polymeric molecule completely different 0:10:06.040,0:10:15.360 from DNA and RNA. In proteins, the monomers are  called amino acids, and there are typically 20 0:10:15.360,0:10:22.120 different ones, each with its own specific  chemical properties. Translation is based on 0:10:22.120,0:10:31.280 base complementarity between the codon on mRNA (a  copy of the gene) and the anticodon on tRNA (the 0:10:31.280,0:10:39.000 carrier of amino acids). It utilizes the genetic  code - a system of rules for encoding amino 0:10:39.000,0:10:49.880 acids. While transcription occurs in the nucleus,  translation occurs on ribosomes in the cytoplasm. 0:10:49.880,0:10:56.360 Pairing of codons and anticodons is a fundamental  mechanism for translating genetic information 0:10:56.360,0:11:04.120 into protein. The mRNA molecule brings the  genetic information to the site of translation. 0:11:04.120,0:11:12.520 tRNA molecules bring amino acids attached to  them. Each tRNA is specific for a particular 0:11:12.520,0:11:20.480 amino acid and distinguishes itself from  other tRNAs by its anticodon. For example, 0:11:20.480,0:11:29.920 a tRNA with the anticodon CGU always carries the  amino acid alanine. And during translation, this 0:11:29.920,0:11:42.640 tRNA can only bind to the GCA codon on the mRNA. In translation, the amino acid sequence is 0:11:42.640,0:11:51.560 determined by the nucleotide sequence in the  mRNA. Each triplet of adjacent ribonucleotides 0:11:51.560,0:11:59.080 specifies one amino acid of the protein, with  the identity of the amino acid corresponding to 0:11:59.080,0:12:08.960 each triplet determined by the genetic code. The  genetic code is a system of rules for translation; 0:12:08.960,0:12:16.040 it is essentially a translation dictionary  that is universal, i.e., with a few exceptions, 0:12:16.040,0:12:23.480 the same for all organisms in the world. Formally,  the genetic code is usually displayed in the 0:12:23.480,0:12:33.040 form of a table or graph to allow easy reading.  There are 64 codons in total, of which three are 0:12:33.040,0:12:42.680 nonsense (stop codons) and one is an initiation  codon (also encodes the amino acid methionine). 0:12:42.680,0:12:50.080 The function of a stop codon is to stop the  synthesis of a polypeptide, so it must always be 0:12:50.080,0:12:59.440 at the end of the coding sequence of a gene. Since  there are 20 basic amino acids, the genetic code 0:12:59.440,0:13:07.680 is degenerate, i.e. one amino acid can be encoded  by multiple codons, but the opposite is not true, 0:13:07.680,0:13:15.480 i.e. one codon always encodes the same amino  acid. Note that, for example, the amino acid 0:13:15.480,0:13:26.480 leucine can be encoded by 6 different codons,  whereas tryptophan can only be encoded by one. 0:13:26.480,0:13:32.800 The translation process can be divided  into three phases: initiation, elongation 0:13:32.800,0:13:41.520 and termination. In addition to the ribosome,  mRNA and tRNA, additional proteins are required 0:13:41.520,0:13:49.880 for the successful completion of each phase.  mRNA binds to a small subunit of the ribosome 0:13:49.880,0:13:58.760 along with initiation factors. The initiation  complex tRNAmet binds to the mRNA codon sequence 0:13:59.280,0:14:09.520 AUG with its anticodon UAC in the peptidyl  site. The large subunit of the ribosome binds 0:14:09.520,0:14:19.480 to this complex. A second activated tRNA with the  bound amino acid enters the A site and a peptidyl 0:14:19.480,0:14:28.960 bond is formed between the two amino acids. The  first tRNA without the amino acid is dissociated 0:14:28.960,0:14:41.120 to form a dipeptide bound to the second tRNA. The mRNA strand is shifted by three nucleotides, 0:14:41.120,0:14:49.240 i.e. the second tRNA is shifted to the P site  and the third tRNA can bind to the mRNA at the 0:14:49.240,0:14:56.320 A site. In this way, the amino acid sequence  is elongated exactly according to the genetic 0:14:56.320,0:15:05.600 information in the mRNA. Once the stop codon in  the mRNA is reached, the process is terminated, 0:15:05.600,0:15:12.960 the whole complex breaks down and the protein  is released. This is then further modified in 0:15:12.960,0:15:19.560 various cellular organelles to produce  the final 3D spatial structures that 0:15:19.560,0:15:27.880 enable the final function of the protein. And this is all for this short presentation 0:15:27.880,0:15:35.600 explaining the basics of expression of genetic  information. Thank you for your attention.