Jean Schernoff
04-07-2002, 01:47 PM
The important element of a protein molecule is the sequence in which amino acids are linked together. This sequence is determined by a genetic code in DNA. The genetic code consists of the sequence of nitrogeneus (sp?) bases in the DNA. In order for protein synthesis to occur, there are several essential materials that must be present: a supply of the 20 different amino acids, which comprise most proteins; a series of enzymes; DNA; and ribonucleic acid - RNA.
RNA carries instructions from the nuclear DNA into the cytoplasm where protein is synthesized. RNA is similar to DNA, with the two exceptions; RNA contains the carbohydarte ribose rather than deoxyribose; and RNA nucleotides contain the pyrimidine uracil, rather than thymine.
RNA and DNA
Like proteins, nucleic acids are very large molecules composed of building blocks. The units of bucleic acids are called nucleotides. Each nucleotide contains a carbohydrate molecule bonded to a phosphate group and to a nitrogen-containing molecule called a nitrogenous base because it has basic properties.
Two important kinds of nucleic acids are found in cells of the human body. One type is deoxyribonucleic acid - DNA; and the other is known as ribonucleic acid - RNA. DNA is found primarily in the 46 chromosomes of the cell nucleus; it is the material of which the genes are composed. RNA is found in the nucleus, ucleous, and cytoplasm of the cell. It participates with DNA in the synthesis of protein.
DNA and RNA differ slightly in the components of their nucleotides. DNA contains the five-carbon carbohydrate deoxyribose, while RNA has ribose. Both DNA and RNA have phosphate groups derived from a molecule of phosphoric acid. The phosphate groups connect the deoxyribose or ribose molecules to one another in the nucleotide chain. Both compounds contain the nitrogenous bases adenine, guanine, and cytosine, but DNA contains the base thymine, while RNA has uracil. Adenine and guanine are purine molecules, while cytosine, thymine, and uracil are pyrimidine molecules.
Note:
In 1953, the biochemists James D. Watson and Francis H.C. Crick (Can someone revise their names, I can be wrong) proposed a model for tne structure of DNA that is now almost universally accepted. In the Watson-Crick model, DNA consists of two long chains of nucleotides. Guanine and cytosine line up opposite one another, and adenine and thymine oppose each other. Adenine and thymine are said to be complementary, as are guanine and cytosine. This is the principle of complementary base pairing. The two nucleotide chains then twist to form a double helix resembling a spiral staircase. Weak hydrogen bonds existing between the chains hold the chains together.
Before a cell divides, DNA replicates itself. In human cells, this implies that 46 chromosomes (46 molecules of DNA) replictae to form 94 (Is it 94 or 92?) chromosomes. Later, the replicated chromosomes separate, and 46 pass into each new cell.
The process of DNA replication begins when specialized enzymes pull apart or unzip the DNA double helix. As the two strands separate, the purine and pyrimidine bases on each strand are exposed. The bases attract their complementary bases, causing them to stand opposite. Deoxyribose molecules and phosphate groups are brought into the molecule, and the enzyme DNA polymerase unites all the nucleotide components to form a long strand of nucleotides. By this process, the old strand of DNA directs the synthesis of a new strand of DNA through complementary base pairing. The old strand then unites with the new strands to reform a double helix. This process is called semiconservetive (sp?) replication, because one of the old strands is conserved in the new DNA double helix.
Types of RNA
In the synthesis of protein, three different types of RNA function. The first type, called ribosomal RNA (nRNA), is used to manufacture ribosomes. Ribosomes are particles of RNA and protein in the cytoplasm where amino acids are linked together. In human cell, ribosomes usually exist along the membranes of the endoplasnic reticulum (sp?). A second important type of RNA is transfer RNS (tRNA). Molecules of tRNA exist free in the cytoplasm of cells and carry amino acids to the ribosomes during protein synthesis. The thrid form of RNA is messenger RNA (mRNA). Messenger RNA receives the genetic code in DNA and carries the code into the cytoplasm. The genetic information is this transferred from the DNA molecule to the mRNA molecule, which is used to synthesize a protein at a distant location.
One of the first processes in protein synthesis is transcription. In this process, a strand of mRNA is synthesized accroding to the nitrogenous base code of DNA. The enzyme RNA polymerase binds to one of the DNA molecules in the double helix and moves along the DNA strand reading the nucleotides one by one. The enzyme selects complementary bases from available nucleotides and positions them in the mRNA molecule according to the principle of complementary base pairing. If a cytosine molecule exists on the DNA, then a guanine molecule is positioned on the RNA, and vice versa. If there is a thymine exists on DNA then an adenine molecule is inserted to RNA. The chain of mRNA lengthens until a stop message is received. The nucleotides of the DNA strands are read in groups of three bases called codons. A codon may be CGA (cytosine-guanine-adenine), TTA or GCT or any other combination of the four bases. The codons are transribed to a complemetary series of codons in the mRNA molecule. The synthesis of mRNA ends, and the mRNA molecule then passes through a pore in the nucleus and proceeds into the cytoplasm toward the ribosomes. Meanwhile, the DNA molecule rewinds to form a double helix.
Translation is the process in which the genetic code is translated to an amino acid sequence in protein. The process begins with the arrival of the mRNA molecule at the ribosome. During this time, tRNA molecules have been uniting with their amino acids. The tRNA molecules now bring their amino acid molecules to ribosomes to meet the mRNA molecule.
After it arrives at the ribosome, the mRNA molecule exposes it's bases in sets of three (a codon). A tRNA molecule has an anticodon that complements each of the codons. When the codon of the mRNA molecule meets with its anticodon on the tRNA molecule, the latter positions it's amino acid as a particular spot. Not the next codon of the mRNA is exposed, and the complementary anticodon of a tRNA molecule complements it. The amino acid carried by that tRNA molecule is positioned next to the first amino acid, and the amino acids are chemically linked to one another. The tRNA molecules then release their amino acids at the ribosome and return to cytoplasm to search out new molecules of their amino acids. Back at ribosome, the next amino acid is positioned into the growing chain as the ribosome moves further down the mRNA molecule. Chain formation continues one amino acid at a time, until the protein is complete. Once the protein has been synthesized, it is removed from the ribosome for further processing. The protein may be modified in the Golgi body and stored in secretory vesicles before release by the cell; or it may be stored in the lysosome as a digestive enzyme, or used in the cell as the structural cellular component. The mRNA molecule is broken up and it's nucleotides are returned to the nucleus. The tRNA molecules wait in the cytoplasm to unite with fresh molecules of amino acids, and the ribosome anticipates the arrival of a new mRNA molecule.
Gene Control
The process of protein synthesis occurs at intervals followed by periods of genetic silence. Gene expression is regulated and controlled by the cell because it would be uneconomical for the cell to be producing all its proteins all the time. For example, a digestive protein is produced when a particular food is consumed. In addition, certain cells produce only certain proteins. For example, a pancreas cell produces the hormone insulin , but a brain cell does not.
The control of gene expression occurs at several levels in the cell. For example, genes are held in control during the process of mitosis. The chromatin is compacted and tightly coiled, and this coiling regulates access to the genes.
Gene control can also occur at transcription and afterwards. In transcription, certain segments of DNA increase the activity of nearby genes and accelerate gene activity. Moreover, after transcription has taken place, the mRNA molecule is altered to regulate gene activity. It has been found, for example, that an mRNA molecule contains many useless bits of RNA called intons (sp?). Intons do not appear to have any genetic information for the synthesis of proteins and are found in all human cells, but not in basterial and other simple cells. They appear to be a sort of genetic gibberish. These bits of RNA are removed in the production of the final mRNA molecule. Exons are the actual genes used to encode the proteins of the cell. They form about 5 percent of all genetic material of human cell, and represent the expressed portion of the human genome. In removing introns and retaining the exons, the cell alters the message received from the DNA and controls gene expression.
There is a whole science behind genetics, this was just a description. I hope I helped!
Best Regards,
Jean
RNA carries instructions from the nuclear DNA into the cytoplasm where protein is synthesized. RNA is similar to DNA, with the two exceptions; RNA contains the carbohydarte ribose rather than deoxyribose; and RNA nucleotides contain the pyrimidine uracil, rather than thymine.
RNA and DNA
Like proteins, nucleic acids are very large molecules composed of building blocks. The units of bucleic acids are called nucleotides. Each nucleotide contains a carbohydrate molecule bonded to a phosphate group and to a nitrogen-containing molecule called a nitrogenous base because it has basic properties.
Two important kinds of nucleic acids are found in cells of the human body. One type is deoxyribonucleic acid - DNA; and the other is known as ribonucleic acid - RNA. DNA is found primarily in the 46 chromosomes of the cell nucleus; it is the material of which the genes are composed. RNA is found in the nucleus, ucleous, and cytoplasm of the cell. It participates with DNA in the synthesis of protein.
DNA and RNA differ slightly in the components of their nucleotides. DNA contains the five-carbon carbohydrate deoxyribose, while RNA has ribose. Both DNA and RNA have phosphate groups derived from a molecule of phosphoric acid. The phosphate groups connect the deoxyribose or ribose molecules to one another in the nucleotide chain. Both compounds contain the nitrogenous bases adenine, guanine, and cytosine, but DNA contains the base thymine, while RNA has uracil. Adenine and guanine are purine molecules, while cytosine, thymine, and uracil are pyrimidine molecules.
Note:
In 1953, the biochemists James D. Watson and Francis H.C. Crick (Can someone revise their names, I can be wrong) proposed a model for tne structure of DNA that is now almost universally accepted. In the Watson-Crick model, DNA consists of two long chains of nucleotides. Guanine and cytosine line up opposite one another, and adenine and thymine oppose each other. Adenine and thymine are said to be complementary, as are guanine and cytosine. This is the principle of complementary base pairing. The two nucleotide chains then twist to form a double helix resembling a spiral staircase. Weak hydrogen bonds existing between the chains hold the chains together.
Before a cell divides, DNA replicates itself. In human cells, this implies that 46 chromosomes (46 molecules of DNA) replictae to form 94 (Is it 94 or 92?) chromosomes. Later, the replicated chromosomes separate, and 46 pass into each new cell.
The process of DNA replication begins when specialized enzymes pull apart or unzip the DNA double helix. As the two strands separate, the purine and pyrimidine bases on each strand are exposed. The bases attract their complementary bases, causing them to stand opposite. Deoxyribose molecules and phosphate groups are brought into the molecule, and the enzyme DNA polymerase unites all the nucleotide components to form a long strand of nucleotides. By this process, the old strand of DNA directs the synthesis of a new strand of DNA through complementary base pairing. The old strand then unites with the new strands to reform a double helix. This process is called semiconservetive (sp?) replication, because one of the old strands is conserved in the new DNA double helix.
Types of RNA
In the synthesis of protein, three different types of RNA function. The first type, called ribosomal RNA (nRNA), is used to manufacture ribosomes. Ribosomes are particles of RNA and protein in the cytoplasm where amino acids are linked together. In human cell, ribosomes usually exist along the membranes of the endoplasnic reticulum (sp?). A second important type of RNA is transfer RNS (tRNA). Molecules of tRNA exist free in the cytoplasm of cells and carry amino acids to the ribosomes during protein synthesis. The thrid form of RNA is messenger RNA (mRNA). Messenger RNA receives the genetic code in DNA and carries the code into the cytoplasm. The genetic information is this transferred from the DNA molecule to the mRNA molecule, which is used to synthesize a protein at a distant location.
One of the first processes in protein synthesis is transcription. In this process, a strand of mRNA is synthesized accroding to the nitrogenous base code of DNA. The enzyme RNA polymerase binds to one of the DNA molecules in the double helix and moves along the DNA strand reading the nucleotides one by one. The enzyme selects complementary bases from available nucleotides and positions them in the mRNA molecule according to the principle of complementary base pairing. If a cytosine molecule exists on the DNA, then a guanine molecule is positioned on the RNA, and vice versa. If there is a thymine exists on DNA then an adenine molecule is inserted to RNA. The chain of mRNA lengthens until a stop message is received. The nucleotides of the DNA strands are read in groups of three bases called codons. A codon may be CGA (cytosine-guanine-adenine), TTA or GCT or any other combination of the four bases. The codons are transribed to a complemetary series of codons in the mRNA molecule. The synthesis of mRNA ends, and the mRNA molecule then passes through a pore in the nucleus and proceeds into the cytoplasm toward the ribosomes. Meanwhile, the DNA molecule rewinds to form a double helix.
Translation is the process in which the genetic code is translated to an amino acid sequence in protein. The process begins with the arrival of the mRNA molecule at the ribosome. During this time, tRNA molecules have been uniting with their amino acids. The tRNA molecules now bring their amino acid molecules to ribosomes to meet the mRNA molecule.
After it arrives at the ribosome, the mRNA molecule exposes it's bases in sets of three (a codon). A tRNA molecule has an anticodon that complements each of the codons. When the codon of the mRNA molecule meets with its anticodon on the tRNA molecule, the latter positions it's amino acid as a particular spot. Not the next codon of the mRNA is exposed, and the complementary anticodon of a tRNA molecule complements it. The amino acid carried by that tRNA molecule is positioned next to the first amino acid, and the amino acids are chemically linked to one another. The tRNA molecules then release their amino acids at the ribosome and return to cytoplasm to search out new molecules of their amino acids. Back at ribosome, the next amino acid is positioned into the growing chain as the ribosome moves further down the mRNA molecule. Chain formation continues one amino acid at a time, until the protein is complete. Once the protein has been synthesized, it is removed from the ribosome for further processing. The protein may be modified in the Golgi body and stored in secretory vesicles before release by the cell; or it may be stored in the lysosome as a digestive enzyme, or used in the cell as the structural cellular component. The mRNA molecule is broken up and it's nucleotides are returned to the nucleus. The tRNA molecules wait in the cytoplasm to unite with fresh molecules of amino acids, and the ribosome anticipates the arrival of a new mRNA molecule.
Gene Control
The process of protein synthesis occurs at intervals followed by periods of genetic silence. Gene expression is regulated and controlled by the cell because it would be uneconomical for the cell to be producing all its proteins all the time. For example, a digestive protein is produced when a particular food is consumed. In addition, certain cells produce only certain proteins. For example, a pancreas cell produces the hormone insulin , but a brain cell does not.
The control of gene expression occurs at several levels in the cell. For example, genes are held in control during the process of mitosis. The chromatin is compacted and tightly coiled, and this coiling regulates access to the genes.
Gene control can also occur at transcription and afterwards. In transcription, certain segments of DNA increase the activity of nearby genes and accelerate gene activity. Moreover, after transcription has taken place, the mRNA molecule is altered to regulate gene activity. It has been found, for example, that an mRNA molecule contains many useless bits of RNA called intons (sp?). Intons do not appear to have any genetic information for the synthesis of proteins and are found in all human cells, but not in basterial and other simple cells. They appear to be a sort of genetic gibberish. These bits of RNA are removed in the production of the final mRNA molecule. Exons are the actual genes used to encode the proteins of the cell. They form about 5 percent of all genetic material of human cell, and represent the expressed portion of the human genome. In removing introns and retaining the exons, the cell alters the message received from the DNA and controls gene expression.
There is a whole science behind genetics, this was just a description. I hope I helped!
Best Regards,
Jean