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DNA or deoxyribonucleic acid is the molecule that carries the genetic information in all cellular forms of life and some viruses. It belongs to a class of molecules called the nucleic acids, which are polynucleotides — that is, long chains of nucleotides. The backbone of the polynucleotide is a chain of sugar and phosphate molecules. Each of the sugar groups in this sugar-phosphate backbone is linked to one of the four nitrogenous bases. The bases link across the two strands in a specific manner using hydrogen bonds: cytosine C pairs with guanine G , and adenine A pairs with thymine T.

The double helix of the complete DNA molecule resembles a spiral staircase, with two sugar phosphate backbones and the paired bases in the centre of the helix. This structure explains two of the most important properties of the molecule. Second, it can store information in the linear sequence of the nucleotides along each strand. It is the order of the bases along a single strand that constitutes the genetic code. Individual codons code for specific amino acids. There are a two points to note about the genetic code:.

The enzyme helicase breaks the hydrogen bonds holding the two strands together, and both strands can then act as templates for the production of the opposite strand. The process is catalysed by the enzyme DNA polymerase, and includes a proofreading mechanism. The gene is the basic physical and functional unit of heredity. It consists of a specific sequence of nucleotides at a given position on a given chromosome that codes for a specific protein or, in some cases, an RNA molecule.

Read more about gene expression and regulation. A human being has 20, to 25, genes located on 46 chromosomes 23 pairs. These genes are known, collectively, as the human genome. The nucleus of each cell in our bodies contains approximately 1. This DNA is tightly packed into structures called chromosomes , which consist of long chains of DNA and associated proteins.

In eukaryotes, DNA molecules are tightly wound around proteins — called histone proteins — which provide structural support and play a role in controlling the activities of the genes. A strand to nucleotides long is wrapped twice around a core of eight histone proteins to form a structure called a nucleosome. The chains of histones are coiled in turn to form a solenoid , which is stabilised by the histone H1.

Further coiling of the solenoids forms the structure of the chromosome proper. Each chromosome has a p arm and a q arm. In their replicated form, each chromosome consists of two chromatids. The chromosomes — and the DNA they contain — are copied as part of the cell cycle, and passed to daughter cells through the processes of mitosis and meiosis.

Read more about the cell cycle, mitosis and meiosis. Human beings have 46 chromosomes, consisting of 22 pairs of autosomes and a pair of sex chromosomes : two X sex chromosomes for females XX and an X and Y sex chromosome for males XY. One member of each pair of chromosomes comes from the mother through the egg cell ; one member of each pair comes from the father through the sperm cell.

A photograph of the chromosomes in a cell is known as a karyotype. The autosomes are numbered in decreasing size order. Most bacteria contain a single, circular chromosome. There are exceptions: some bacteria — for example, the genus Streptomyces — possess linear chromosomes, and Vibrio cholerae, the causative agent of cholera, has two circular chromosomes.

The chromosome — together with ribosomes and proteins associated with gene expression — is located in a region of the cell cytoplasm known as the nucleoid.

The genomes of prokaryotes are compact compared with those of eukaryotes, as they lack introns, and the genes tend to be expressed in groups known as operons. The circular chromosome of the bacterium Escherichia coli consists of a DNA molecule approximately 4. In addition to the main chromosome, bacteria are also characterised by the presence of extra-chromosomal genetic elements called plasmids. These relatively small circular DNA molecules usually contain genes that are not essential to growth or reproduction.

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Learn how your comment data is processed. Lanjut ke konten. DNA, genes and chromosomes. DNA DNA or deoxyribonucleic acid is the molecule that carries the genetic information in all cellular forms of life and some viruses. Each nucleotide consists of three components: a nitrogenous base: cytosine C , guanine G , adenine A or thymine T a five-carbon sugar molecule deoxyribose in the case of DNA a phosphate molecule The backbone of the polynucleotide is a chain of sugar and phosphate molecules.

Double strand of polynucleotides The double helix of the complete DNA molecule resembles a spiral staircase, with two sugar phosphate backbones and the paired bases in the centre of the helix. DNA helix showing nitrogenous bases It is the order of the bases along a single strand that constitutes the genetic code. There are a two points to note about the genetic code: It is universal. All life on Earth uses the same code with a few minor exceptions.

It is degenerate. Each amino acid can be coded for by more than one codon. A codon table sets out how the triplet codons code for specific amino acids. DNA replication The enzyme helicase breaks the hydrogen bonds holding the two strands together, and both strands can then act as templates for the production of the opposite strand.

Genes The gene is the basic physical and functional unit of heredity. Genes consist of three types of nucleotide sequence: coding regions, called exons, which specify a sequence of amino acids non-coding regions, called introns, which do not specify amino acids regulatory sequences, which play a role in determining when and where the protein is made and how much is made The structural components of a gene Read more about gene expression and regulation A human being has 20, to 25, genes located on 46 chromosomes 23 pairs.

Chromosome unraveling to show the base pairings of the DNA The chromosomes — and the DNA they contain — are copied as part of the cell cycle, and passed to daughter cells through the processes of mitosis and meiosis. Read more about the cell cycle, mitosis and meiosis Human beings have 46 chromosomes, consisting of 22 pairs of autosomes and a pair of sex chromosomes : two X sex chromosomes for females XX and an X and Y sex chromosome for males XY.

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Gene expression is the process by which the genetic code — the nucleotide sequence — of a gene is used to direct protein synthesis and produce the structures of the cell. Translation : the use of mRNA to direct protein synthesis, and the subsequent post-translational processing of the protein molecule. Transcription is the process of RNA synthesis, controlled by the interaction of promoters and enhancers. In translation the mature mRNA molecule is used as a template to assemble a series of amino acids to produce a polypeptide with a specific amino acid sequence. The complex in the cytoplasm at which this occurs is called a ribosome. Ribosomes are a mixture of ribosomal proteins and ribosomal RNA rRNA , and consist of a large subunit and a small subunit.

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Materi Review Genetika dan Biologi Molekuler : DNA, genes and chromosomes

DNA or deoxyribonucleic acid is the molecule that carries the genetic information in all cellular forms of life and some viruses. It belongs to a class of molecules called the nucleic acids, which are polynucleotides — that is, long chains of nucleotides. The backbone of the polynucleotide is a chain of sugar and phosphate molecules. Each of the sugar groups in this sugar-phosphate backbone is linked to one of the four nitrogenous bases. The bases link across the two strands in a specific manner using hydrogen bonds: cytosine C pairs with guanine G , and adenine A pairs with thymine T.

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Materi Review Genetika dan Biologi Molekuler : Gene expression and regulation

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