LESSON 1: HOW PROTEIN IS MADE USING INFORMATION FROM DNA

Different types of proteins exist in every living organism. Protein is the most varied molecule in which the human body contains at least 10,000 different kinds of proteins. Since the human body is made up of cells, their unique characteristics are determined by the type of proteins they possess. For example, the red blood cells are able to carry oxygen throughout the body because they contain a protein that is not found in other cells. Another example is that the muscle cells are made up of fibrous protein which allows the movement of the muscle to contract and relax. Body covering of the body such as the skin, nail, and hair contain a kind of protein that makes them tough and horny.

The proteins that occur in the body are large, complex molecules composed mainly oxygen, hydrogen, carbon, and nitrogen. Proteins are essential part structure of cells. It acts as an enzyme or catalyst for chemical reactions in cells.

Amino Acid

Amino acids are the building blocks of proteins, which are made up of long chains of chemical units. There are 20 different amino acids. Our body system can synthesize non-essential amino acids through metabolic process from simple organic molecules and the nine essential amino acids must be obtained from the dietary food we intake.

IMPORTANCE OF PROTEINS IN THE BODY

1. Protein hormones regulate many physiological processes, like insulin, that affects glucose transport into cells.
2. Proteins in the blood help as blood clotting factor and transport molecule. For instance, hemoglobin transports oxygen in the blood.
3. Protein acts as ion channels, carrier, and receptor molecules in the cell membrane.

THE THREE KINDS OF RNA IN PROTEIN SYNTHESIS

There are three kinds of RNA in which cells build proteins. This process is called protein synthesis.

1. Messenger RNA (mRNA) is a type of molecule of RNA that travels from the nucleus to the ribosomes in the cytoplasm, where the information in the copy is used for a protein product.
2. Ribosomal RNA (rRNA) is the RNA component of the ribosome and a cell's protein factory in all living cells. It provides a mechanism for decoding mRNA into amino acid and interacts with tRNA.
3. Transfer RNA (tRNA) is an adaptor molecule composed of RNA, typically 73 to 93 nucleotides in length that brings amino acids from the cytoplasm to a ribosome to help make the growing protein.

The genetic code is shared by all organisms. For instance, you want to determine which amino acid is encoded by CAU codon. First, find the first base C from the first nucleotides in the left part of the Genetic Code. Then, find the second base A from the second nucleotides on the upper part. Finally, find the third base U from the third nucleotides in the right side of the Genetic Code. Hence, we find the amino acid histidine as encoded by codon CAU.

DNA POLYMERASE

Enzymes and other proteins are responsible for the process of replication. An enzyme begins the process by unzipping the double helix to separate the strands of DNA. Some proteins hold the strands apart, which serve as the template. The floating free nucleotides in the nucleus will be paired with the nucleotide of the existing DNA strand. The DNA polymerase (group of enzymes) is responsible in bonding the new nucleotide together. When the process is done, it forms two complete molecules of DNA, each exactly the same the original double strand.

THE REPLICATION PROCESS

Before the cell of an organism can reproduce, it must first replicate or make a copy of their DNA. Copy of the DNA happens whether the cell is prokaryote or a eukaryote. The following steps describe the replication of DNA in both eukaryotic and prokaryotic cells:

1. DNA replication takes place in the cytoplasm of prokaryotes and in the nucleus of eukaryotes. The enzymes start to unzip the double helix as the nucleotide base pairs separate. Each side of the double helix runs in opposite directions. At same time, replication begins on both strands of the molecules.
2. Free nucleotides pair with the base exposed as the template strand continuously unzip, an enzyme complex-DNA polymerase attaches the nucleotide together to form a new strand similar to each template.
3. A sub-unit of the DNA polymerase proofreads the new DNA and the DNA ligase (enzyme) seals up the fragments into one long strand.
4. Two similar double-stranded molecules of DNA result from replication. The new copies automatically wind up again. According to Nowick, "DNA replication is semi-conservative because one old strand is conserved, and a new strand is made."

PROCESSES OF PRODUCING PROTEIN FROM DNA

1. Transcription

The DNA is found inside the nucleus of the cells which are embedded in the chromosomes. The genetic information within the DNA must be transported to the ribosome in the cytoplasm where protein synthesis takes place. The genetic information or code is copied into the mRNA through the process of transcription. The transcription process occurs when the nucleotide sequence along the DNA is copied into a strand of mRNA. The DNA strand will be exposed once the DNA molecule uncoils. The RNA polymerase is responsible for the alignment and binding together of the ribonucleotides that will create the single strand of RNA molecule. The mRNA molecule, as the complimentary ribonucleotides, attach to the exposed bases of the DNA strand.

2. Translation

Translation is the final step in the synthesis of a small protein through the help of the mRNA. The transfer of code from the mRNA to a small protein begins when the mRNA molecule attaches to the ribosome, which forms the mRNA-ribosome complex. The different amino acids found in the cytoplasm must first be transferred in the mRNA-ribosome complex by another RNA. An amino acid is then attached to a specific transfer RNA (tRNA). There are as plenty of tRNA as to the presence of amino acids because it is intended that each tRNA is coded to specific kind of amino acid. Translation is the converting the information from the RNA into a protein. Each tRNA with its attached specific amino acid moves to the mRNA-ribosome complex.

The ribosome changes its position by three nucleotides. The tRNA without the amino acid is detached from the ribosome. The ribosome now shifts to the next codon, ready to bind another tRNA with its specific amino acid. The mRNA codon recognizes which tRNA is next, as a result, specifying which amino acid will be next in the polypeptide (addition of amino acids to the protein) chain. The process is repeated as the ribosome goes along the mRNA chain. A codon in the mRNA stops when the ribosome encounters the addition of amino acids to the protein.

LESSON 2: MUTATIONS THAT OCCUR IN SEX CELLS AS BEING HERITABLE

Many types of mutation can occur in an organism's DNA. Biologically, mutation is the change in genetic material. It can be a source of beneficial genetic variation or it may have dangerous effects. Mutations can result from DNA copying mistakes made during cell division, and exposure to ionizing radiation like gamma rays from radioactive elements such as uranium and plutonium. Another cause of DNA copying mistakes is direct exposure to chemicals or through infection by bacteria and viruses. The different types of agents, whether they are in the form of physical or chemical that can cause the alteration of the structure or sequence of DNA, are called mutagens.

MUTATIONS OCCURRING IN SEX CELLS

How are genetic traits or characteristics passed on from parents to their child? What do you think can determine the combination of traits that are passed on? Mutations that occur in sex cells can be passed from parent to their children. Since the chromosomes carry information about the characteristics inherited from parents, it is better to have a clear understanding on the structure of a chromosome. Chromosome is made up of a chemical substance called deoxyribonucleic acid or DNA. Most of the cells in the body contain 23 pairs of chromosomes (46 sets of chromosomes). The sex cells contain half this number. When a sperm and egg cell unite, the fertilized egg ends up with 46 chromosomes, which are 23 chromosomes from each parent. The chromosome contains many genes, a section of a chromosome that determines a single trait. Genes are the basic unit of heredity. Once the egg is fertilized, it may now contain two genes for each trait - one from the father and one from the mother. This is how hereditary information is passed from one generation to the next. Do you think defective genes can be inherited?

SOMATIC AND GERMINAL MUTATION

Eukaryotic organisms, such as mammals, humans, amphibians, avians, and vascular plants, have two primary cell types: the germ and the somatic. Mutations can occur in either of the two cell types. Mutation in somatic cells is called somatic mutation. It occurs in non-reproductive cells and will not be passed onto the offspring. They do not occur in cells that give rise to sex cells (sperm and egg cell). Therefore, mutation will not be passed along to the next offspring by sexual means.

Germinal mutation is an alteration of the nucleotide sequence of the DNA that makes up a gene. The germ cells give rise to sex cells that will carry the mutations that will be passed on to the next generation, when a successful mating happened. Generally, this type of mutation is not expressed in the individual offspring containing the mutation, but it would be expressed in either negative or positive affected sex cell production. For instance, Queen Victoria of England introduced the hemophilia allele into a few number of the royal families of Europe. The germ line mutation carried by the queen was passed to their generation.

CHROMOSOME MUTATIONS

Chromosome mutations are departures from what is normal or desirable set of chromosomes either for an individual or from a species. It refers also to changes in the number sets of chromosome (-ploidy) and changes in the number of individual chromosomes (-somy) and its appearance. There are several kinds of chromosomal mutations which are enumerated below.

INSERTION

Insertion is a genetic material added from another chromosome.

TRANSLOCATION

Translocation happens when part of a chromosome breaks off and combined to another chromosome. This type of disorder is due to chromosomal level mutation.

DELETION

Deletion happens when there is loss of part of a chromosome.

DUPLICATION

Duplication happens if there are extra copies of a part of a chromosome.

INVERSION

Inversion happened when the direction of a part of a chromosome is reversed.

GENETIC DISORDERS

1. Recessive Disorders

Recessive disorders happen when a child receives two defective genes from each parent. A person who receives one defective recessive gene is called a carrier. The carrier does not express the disorder because it is not detectable by the dominant normal gene. Therefore, it can pass the defective gene to their children.

• a. Sickle cell anemia is a genetic blood disorder. A person who inherits two defective genes will have abnormally shaped red blood cells and may die at an early stage.
• b. Tay-Sachs disease is characterized by the lack of an important chemical in the brain. Infants who have this kind of disease usually die within their first five years.

• c. Phenylketonuria or PKU is a rare genetic disorder that can cause serious mental retardation in infants. An infant who has this kind of disorder cannot break down phenylalanine (chemical commonly found in food) that it builds up in the body, in which the brain is affected. Phenylalanine is obtained from an artificial sweetener called aspartame. This kind of disease can be treated through a special diet.
• d. Cystic fibrosis is a disease in which some glands produce too much mucus that it clogs and damages the lungs. This disease is fatal among children because it causes difficulty in breathing.

2. Sex-linked Disorders

Sex-linked disorders are more common in men because they have only one X chromosome, so all defective genes on the chromosome will be expressed. Since women carry two X chromosomes, a recessive defective gene on one X chromosome can be covered by a normal gene on the other X-chromosome. A woman who has this kind of disease may pass it on to her children. The most common sex-linked disorder is color blindness and hemophilia.

3. Human Genetic Syndrome

There are some genetic disorders that may have few or too much chromosomes. A person who survived during chromosomal mutations is categorized by a distinctive set of mental or physical abnormalities.

• a. Cri du chat is caused by the deletion of part of the short arm of chromosomes 5. Babies who have this disease have wide-set eyes and a small head and jaw.
• b. William syndrome is the result from the loss of a segment in chromosome 7. They have large ears and facial features that make them look like elves.
• c. Down syndrome (trisomy 21) is known as Mongolism. A child receives an extra chromosome (chromosome 21) and has a distinctive physical appearance. It is the most common cause of mental retardation. It can be mild or severe mental retardation.

• d. Edward syndrome (trisomy 18) happens when there is an extra number 18 chromosome. It shows mental retardation and physical abnormalities to the child and can live beyond one year.
• e. Patau's syndrome (trisomy 13) is caused by an extra copy of number 13 chromosome. Based on the study, about 90% of babies with this syndrome do not survive in infancy. Severe mental retardation occurred in those who survived.

• f. Klinefelter's syndrome (XXY) is another genetic disorder. A male who has this syndrome has two or more X-chromosomes in addition to their Y chromosomes. They lack facial hair and their testes, including the prostate gland, are underdeveloped.
• g. Turner's syndrome has 45 chromosomes. About 96-98% with this condition do not survive at birth. It is a genetic disorder that affects women. Those who survived with this condition usually have no menstruation, have narrow hips, breasts that are not developed, and broad shoulders and neck.

IMPACT OF MUTATION ON PHENOTYPE

Mutations of the chromosome directly affect the genes which can cause human genetic disorders. The gene can no longer do its tasks normally once it breaks up due to mutation. Gene mutation has a great impact on the organism. For instance, substitution occurs in a coding region of DNA. If substitution happens, the enzymes are not able to bind to its substrate, so the mutation directly affects protein folding. Thus, it damages the protein's function. There is also a premature stop codon.

Gene mutations sometimes do not affect an organism's phenotype due to many codons that code for the same amino acid. A mutation that has no effect on the protein is called silent mutation. Most of the amino acids of silent mutation are encoded by many different codons. For instance, if the third base in the TCT codon for serine becomes different to any one of the other bases, it can still be encoded. It is called silent mutation since there is no change or the product cannot be detected without sequencing the gene. Missense mutation happens when a point of mutation, in which a single nucleotide change, results in different codes of amino acid.

IMPACT OF MUTATION ON OFFSPRING

Mutation occurs in the body cells and in germ cells. Mutations in body cells damage only the organisms in which they occur while in germ cells, mutation may be passed to offspring. In some cases, mutation results in a more beneficial phenotype due to being favored by natural selection and increasing in a population.

CAUSES OF MUTATIONS:

• 1. SMOKING CAN RAISE RISK OF GENETIC MUTATION.

  Smoking can cause germ cell mutagens that can destroy genes and cause cancer and other diseases. If diseases occur, they will be inherited and can be detrimental to the children later in their life. When a mother smokes during her conception, it may lead to genetic alterations in her child.

• 2. EFFECT OF OLD AGE ON OFFSPRING

  Many experts found out that old age at conception had an effect on offspring's intelligence and personality. Healthy and normal eggs produced by females will decline as they get older. There is a chromosomal error happening more frequently in the eggs, resulting in abnormal embryos. Older mothers (aged 36 to 45) are at a higher risk of having a baby with Down syndrome, Patau's syndrome, and Edward's syndrome. For early detection of these diseases, parents should prepare for the special needs of the baby.

• 3. CHEMOTHERAPY

  Chemotherapy drugs can cause DNA mutations to the offspring. The genome affected by chemotherapy drug will not stabilize, resulting in new mutation.

• 4. EXTERNAL INFLUENCES

  Too much exposure to hazardous chemicals and radiation such as x-rays and gamma rays can cause mutations. The DNA will break down. Though the cell repairs the DNA, it can no longer return to the original structure, resulting in new mutations.

LIFE LESSONS

Man's Journey into Earth's Landforms

You had just learned that chromosomes contain many genes, a section of a chromosome that determines a single trait and the genes are the basic unit of heredity. All the traits you possess now are inherited from our parents. We cannot choose what kind of traits we want for ourselves. We do not want to inherit diseases from our parents. We should be thankful if we have good traits and characteristics and a normal physical appearance. We have to understand other people who inherited genetic disorders. We have to help them in our own little way that we really care.