Description of Genes and Alleles

A. Genes and Alleles
 

              Just look at you and your parents, who do you look like? Why are you like your parents? This is because the genes that are owned by your parents are transmitted or passed to you.

Each cell in the organism contains the genetic material. This genetic material is known as a gene found on chromosomes within the nucleus. After studying this chapter, you will discover about the genes, the DNA and the chromosomes, follow the following description.


1. Definition of genes and allelesGenes are the smallest unit of genetic material. Genes are present at each
locusTypical of chromosomes. Genes are the smallest genetic substance consisting of a piece of DNA that determines the nature of the individual through the formation of polypeptides. Therefore, genes play an important role in controlling the properties of inherited individuals.The genes present in the chromosomes have no clear boundaries. However, genes can be compared to a sequential and regular sequence of chromosomal strands.In the cells of the body, the chromosomes are usually in pairs. A pair of chromosomes are homologous to each other, meaning that they both have the same form and corresponding gene locus. The genes present in the corresponding loci are called alleles.2. Functions of genes and allelesGenes are a chemical entity. As hereditary matter, genes have several functions, including:A) As individual particles present on chromosomes. Zarah is the smallest substance and can not be divided again.B) Transmit genetic information from the mother to her offspring.C) Organize metabolic processes and development.The allele may have the same or opposite task for a particular job. The allele that has the same task is called the homozygous allele. While alleles whose different tasks are called heterozygous alleles. Alleles are the same tasks, for example black determining genes in wheat that have pairs of genetic determinants of black as well. Examples of alleles whose work is the opposite are the genetic determinants of black in wheat that have a pair of white determining genes.Cell activity is controlled by genes within the nucleus. This control is performed by arranging certain materials that conform to the genetic pattern to form a chain of amino acids (polypeptides). The polypeptide functions in an enzyme that will regulate the metabolism reaction in the cell.
B DNA and RNAThe compound between proteins and nucleic acids is calledOf the two compounds, only nucleic acids can carry genetic information from the mother to offspring. Thus, in fact, nucleic acid is a genetic material or inheritance factor, although chromosomes are commonly known as inheritance factors. Nucleic acid as a DNA material consists of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). To find out about DNA and RNA, see the following description.1. DNA (deoxyribonucleic acid)Several studies revealed that DNA is the carrier of most or all of the genetic traits within the chromosome. DNA is present in the nucleus and together the protein compound forms the protein core. In addition to the nucleus, DNA molecules are also present in mitochondria, plastids and centrioles.The chemical arrangement of DNA is a complex macromolecule. The DNA molecules are arranged by two very long chains of polynucleotides. A polynucleotide chain consists of a series of nucleotides. A nucleotide is composed of:A) The group sugar deoxyribose (sugar with five carbon atoms or pentose)B) The phosphoric acid group (phosphate bound to the fifth sugar C)C) nitrogen base group (this group is attached to the first sugar C)The nitrogen bases can be divided into two, namely the purine base and the pyrimidine base. The purine base consists of adenine (A) and Guanine (G), while the base of pyrimidine consists of cytosine (S) and thymine (T).The base sugar forms a bond between C in sugar with N on the basis of purine and N-H on the basis of pyrimidine. The compounds that are formed are called nucleosides or deoxyribonucleosides. Nucleosides can be divided into four types, namely:1) Sugar compound with adenine base (deoxy adenosine).2) Sugar compound based on guanine (deoxy guanosine).3) Sugar compound with thymine bases (deokstimmidin).4) Sugar compound with a cytosine base (deoxysitidine).In addition, the phosphates form esters with nucleosides forming C5 bonds in sugars. These phosphate-5-nucleoside esters are referred to as nucleotides. There are 4 types of nucleotides, namely adenosine deoksibribonukleotida, guanosin deoksibribonukleotida, sitidin deoksibribonukleotida, and thymidine deoksibribonukleotida. These nucleotides can be combined to form a circuit called a polynucleotide. The twisted polynucleotide (double-helix) wire forms the DNA. To better understand the structure of nucleotides and polynucleotidesBased on the results of the analysis of X-ray refraction by DNA crystals, James Watson (USA) and Francis Crick (England) concluded in 1953 that the molecular structure of DNA is a double helix.DNA molecules have properties, among others:1) DNA from several organisms has the same adenine content (A) as Timin (T). The difference between the DNA of the different species is between the content of A + T or G + C.2) Each DNA molecule is composed of two polynucleotide chains. The bases of the two chains are paired with adenine rules paired with Timin and Guanin in pairs with cytosine. Hydrogen bonds are formed between the two base pairs. The presence of these bonds provides flexibility to DNA.3) DNA is an active structure that performs biological functions.
2. RNAIn cells of eukaryotic and prokaryotic organisms, in addition to DNA, there is another nucleic acid which is important, namely RNA or ribonucleic acid. RNA is a unique yarn that is composed of ribose sugar molecules, phosphate groups and nitrous acid. Nitrogenous RNA bases consisting of a group of purines (adenine and guanine) and pyrimidine groups (cytosine and uracil).RNA formed by the DNA in the nucleus, through the DNA transcription process. RNA transcript used for the synthesis of proteins in the cellular cytoplasm.Based on the location and function, the RNA can be divided into three types, namely:A) RNA (RNA-d) or mRNARNA messenger is the RNA that became the model template in the process of preparing an amino acid in the polypeptide chain or protein synthesis. Called messenger RNA, because this is the link with DNA and proteins to bring a message of genetic information from the DNA to form protein. Genetic information from the sequence of the base N RNA in order that an amino acid called codons. The preparation of polypeptide chains depends on codon sequences in RNA.Sequences of codons in RNA-d DNA printed depending on the type of protein to be synthesized.B) Transfer RNA (t-RNA)T-RNA have a function for translating codons contained in d-RNA into an amino acid species. The ability to translate this, due to the anticodon is a complement of RNA codon-d. T-RNA also serves to transport amino acids to the surface of the ribosome during translation. Translation is the translation of the nucleotide sequence of d-RNA into an amino acid sequence of the polypeptide.C) ribosomal RNA (r-RNA)R RNA-RNA is the most, approximately 83% of the RNA contained by a cell. RNA-r role in the synthesis of protein chains as a locus of RNA-RNA-d and t.RNA and DNA have differences. Note the difference in Table 3.1 below.Table 3.1 Differences in RNA and DNAFigure 3.8RNA in protein synthesisC ChromosomeThe cores are thin strands like nets that can absorb color. Thin strands called chromatin (chromium = color, and tin = weight). When the cell divides, chromatin strands thicken and shorten, more easily absorb the dye that can be seen with a microscope. The chromatin strands thicken and shorten, called chromosomes.1. Classification of chromosomesBased on the location of the chromosome in the body. Chromosomes divided into two types, namely chromosomes of the chromosomal body (autosomal) and sex (sex chromosomes). In the cells of the body there are a pair of chromosomes or diploids (2n). This pair of chromosomes from the mother (egg) and the male (sperm). Each chromosome is the parent of n chromosomes. Paired chromosomes are called homologous chromosomes. Homologous chromosomes are structures that have the same or have loci alleles therein. In human cells, there are 23 types of homologous chromosomes. The number of chromosomes or a pair of chromosomes called the haploid genome.
A chromosome consists of two parts, namely:1) centromere the kinetokhor. This section is round and contains no genes. The centromere works for the movement of the chromosomes of the equatorial region to the respective poles at the moment of the division2) The arm is the body of the chromosome. Inside this arm is chromomena (protein nucleic material)The location of the centromere is characteristic of each pair of chromosomes. Based on the location of the centromere, chromosomes can be grouped into several types, namely:(1) Metacentric: the centromere is located at the center of the chromosome(2) Submetacentric: centromere closure at one end of the chromosome(3) Axosentic: centromere located near the end of the chromosome(4) Paracentric: centromere located at the end of the chromosome.In addition to the above chromosome classification, the chromosome shape may vary due to the location of several centromere as well. For example, there is a chromosome that resembles the letter L (one arm of the chromosome is longer than the other), the chromosome resembles the letter I (the centromere is at the end of the chromosome), and the chromosome resembles To the letter V (the chromosome has the same arm length).2. Number of ChromosomesIn each organism there is a variable number of chromosomes. The number of haploid chromosomes present in various organisms can be seen in Table 3.2 below.Table 3.2 Number of Chromosomes (2n) in Various Animals and PlantsD Protein SynthesisProteins are a macromolecule made up of several amino acids. Meanwhile, the enzyme is a protein that has the ability to catalyze biochemical reactions in the process of cellular metabolism. Based on the research results of Beadle and Tatum (1941), the gene controls the metabolic process or individual life through the process of controlling the enzyme. Therefore, a change in gene structure may lead to changes in protein structure at the amino acid level, which in turn leads to changes in the metabolic process.Proteins are not synthesized directly by the gene, but through the process of transcription and translation (genes are functional names, the structure is DNA). Transcription is the process of DNA replication to form RNA-d. Translation is the process of translating the genetic information contained in d-RNA into a sequence of amino acid polypeptides. In transcription, DNA is used as a model for protein synthesis. To know more about transcription and translation in protein synthesis, see the following description.1. TranscriptionTranscription is the process of transferring genetic information from the DNA segment (gene) to the RNA molecule guided by the enzyme transcriptase as its catalyst. The basic sequence in the d-RNA strand is determined by the base sequence found in a DNA segment, and each base will search its ribonucleotide counterpart, then will couple to a d-RNA strand.Transcription readings start from the initial sign (promoter) to the end (terminator). Only segments flanked by the two markers will be transcribed. The gene is the protein controller so the gene must be present in the segment between the promoter and the terminator
2 TranslationsAfter the transcription process inside the cell nucleus is complete, then the d-RNA leaves the nucleus to become a template model in the preparation of amino acid sequences in the translation process. The genetic information carried by RNA-d is present in the base of the base it contains. Each of the three combinations of adjacent bases contains a specific genetic code (codon), which can be translated into an amino acid type. In a single strand of d-RNA, only certain parts of the template are formed in protein synthesis, ie, flanked segments by the earliest codon (AUG) and the final codon (UAA, UAG, UGA)After RNA-d reaches the ribosome, RNA-t begins to transport the amino acids in the translation complex (ribosome) as well as the decoding of d-RNA codons. In addition, the amino acids transported by t-RNA are assembled into polypeptides. The ability of the RNA-t to carry out the task is due to the presence of anti-codon codons and the ability of a complex with amino acids called aminoacyl-t RNA.

 The process of translating a number of RNA codons into a number of amino acid polypeptides is called translation. To know the process of transcription and translation in protein synthesis, see Figure 3.12.E Genetic PasswordThe genetic code is the relationship between amino acidsThat is present in the polypeptide chain with the nucleotide sequence contained in d-RNA. Nucleotide sequences are formed based on DNA models in the gene segment. Therefore, a genetic code can be interpreted as a rule of relation between genes and proteins.In nucleic acid or d-RNA DNA there are 4 types of nucleotides (bases) that form the strand. In the polypeptide 20 types of amino acid constituents are known. How is itOf these 20 amino acids, there must be rules that guarantee the control of genes in the formation of proteins, always characteristics (a gene only encodes a type of protein). To ensure this particularity must be many control factors (codons), at least the same as those controlled (amino acids). Its goal is to prevent a codon from controlling more than one amino acid. Under this requirement, it is not possible for an amino acid to be controlled by only one nucleotide, since the four nucleotides present would not be sufficient to control 20 amino acids. The coding system must be based on a combination of existing nucleotides. Most likely, each codon is a combination3 nucleotides of DNA so that 64 codons will be obtained which will be sufficient to control 20 amino acids.Sixty-four of these codons function to encode amino acids, but there will be codons encoding one type of the same amino acid. Therefore, there are 3 codons, ie UAA, UAG and UGA that become the final codon and AUG that became the initial codon, these four codons do not encode amino acids. Most amino acids are controlled by more than 1 codon. The various codons encoding the same type of amino acids are called synonymous codons. It is known that the codons do not overlap and lie side by side without an auctioneer. Thus, amino acid formation will be carried out by a series of d-RNA codons from the codon and terminated by one of the final codons.The concept of genetic code was discovered thanks to the success of researchers who developed the synthesis of proteins and nucleic acids in vitro. To find out this genetic code, see Table 3.3 below.In protein synthesis there may be errors in the translation of received DNA codes. If a translation error occurs, the resulting protein is also incorrectly set up so that the resulting enzyme is also wrong. If this happens, then the metabolism will be interrupted. For example, a GAA codon should be translated into glutamic acid, but for RNA-t reads GUA which translates into valine, or read AAA translated into lysine. This, causing the resulting polypeptide is incompatible with the DNA command.This error affects the process of hemoglobin formation. Normal hemoglobin should contain glutamic acid, but due to translation errors, hemoglobin contains either valine or lysine. This causes hemoglobin to produce sickle cells. The sickle cell causes an abnormality called cycling. Cyclemia is transmitted to offspring and causes mutationsTherefore, the error of t-RNA that interprets genetic codes of DNA is also one of the mechanisms of genetic mutation. Genetic mutations cause a change in hereditary traits.