DNA: STRUCTURE
DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).
DNA is made up of Molecules called nucleotides. Each nucleotide contains a phosphate group, a sugar group and a nitrogen base. The four types of nitrogen bases are adenine (A), thymine (T), guanine (G) and cytosine (C). The order of these bases is what determines DNA’s instructions, or genetic code. Similar to the way the order of letters in the alphabet can be used to form a word, the order of nitrogen bases in a DNA sequence forms genes, which in the language of the cell, tells cells how to make proteins. Another type of nucleic acid, ribonucleic acid, or RNA, translates genetic information from DNA into proteins. The entire human genome contains about3 billion bases and about 20,000 genes.
Nucleotides are attached together to form two long strands that spiral to create a structure called a double helix. If you think of the double helix structure as a ladder, the phosphate and sugar molecules would be the sides, while the bases would be the rungs. The bases on one strand pair with the bases on another strand: adenine pairs with thymine, and guanine pairs with cytosine. DNA molecules are long — so long, in fact, that they can’t fit into cells without the right packaging. To fit inside cells, DNA is coiled tightly to form structures we call Chromosomes. Each chromosome contains a single DNA molecule. Humans have 23 pairs of chromosomes, which are found inside the cell’s nucleus.
Functions of DNA
DNA usually occurs as linear chromosomes in eukaryotes, and circular chromosomes in prokaryotes. The set of chromosomes in a cell makes up its genome; the human genome has approximately 3 billion base pairs of DNA arranged into 46 chromosomes. The information carried by DNA is held in the sequence of pieces of DNA called genes. Transmission of genetic information in genes is achieved via complementary base pairing. For example, in transcription, when a cell uses the information in a gene, the DNA sequence is copied into a complementary RNA sequence through the attraction between the DNA and the correct RNA nucleotides. Usually, this RNA copy is then used to make a matching protein sequence in a process called translation, which depends on the same interaction between RNA nucleotides. In alternative fashion, a cell may simply copy its genetic information in a process called DNA replication. The details of these functions are covered in other articles; here the focus is on the interactions between DNA and other molecules that mediate the function of the genome.
DNA REPLICATION
Process of DNA replication takes place in following steps:
Fork Formation
Before DNA can be replicated, the double stranded molecule must be “unzipped” into two single strands. DNA has four bases called adenine (A), thymine (T), cytosine (C) and guanine (G) that form pairs between the two strands. Adenine only pairs with thymine and cytosine only binds with guanine. In order to unwind DNA, these interactions between base pairs must be broken. This is performed by an enzyme known as DNA helicase. DNA helicase disrupts the hydrogen bonding between base pairs to separate the strands into a Y shape known as the replication fork. This area will be the template for replication to begin. DNA is directional in both strands, signified by a 5′ and 3′ end. This notation signifies which side group is attached the DNA backbone. The 5′ end has a phosphate (P) group attached, while the 3′ end has a hydroxyl (OH) group attached. This directionality is important for replication as it only progresses in the 5′ to 3′ direction. However, the replication fork is bi-directional; one strand is oriented in the 3′ to 5′ direction (leading strand) while the other is oriented 5′ to 3′ (lagging strand). The two sides are therefore replicated with two different processes to accommodate the directional difference.
Primer Binding
The leading strand is the simplest to replicate. Once the DNA strands have been separated, a short piece of RNA called a primer binds to the 3′ end of the strand. The primer always binds as the starting point for replication. Primers are generated by the enzyme DNA primase.
Elongation
ENZYMES known as DNA polymerases are responsible creating the new strand by a process called elongation. There are five different known types of DNA polymerases in bacteria and human cells. In bacteria such as E. coli, polymerase III is the main replication enzyme, while polymerase I, II, IV and V are responsible for error checking and repair. DNA polymerase III binds to the strand at the site of the primer and begins adding new base pairs complementary to the strand during replication. In eukaryotic cells, polymerases alpha, delta, and epsilon are the primary polymerases involved in DNA replication. Because replication proceeds in the 5′ to 3′ direction on the leading strand, the newly formed strand is continuous. The lagging strand begins replication by binding with multiple primers. Each primer is only several bases apart. DNA polymerase then adds pieces of DNA, called Okazaki fragments, to the strand between primers. This process of replication is discontinuous as the newly created fragments are disjointed.
Termination
Once both the continuous and discontinuous strands are formed, an enzyme called exonuclease removes all RNA primers from the original strands. These primers are then replaced with appropriate bases. Another exonuclease “proofreads” the newly formed DNA to check, remove and replace any errors. Another enzyme called DNA ligase joins Okazaki fragments together forming a single unified strand. The ends of the linear DNA present a problem as DNA polymerase can only add nucleotides in the 5? to 3? direction. The ends of the parent strands consist of repeated DNA sequences called telomeres. Telomeres act as protective caps at the end of chromosomes to prevent nearby chromosomes from fusing. A special type of DNA polymerase enzyme called telomerase catalyzes the synthesis of telomere sequences at the ends of the DNA. Once completed, the parent strand and its complementary DNA strand coils into the familiar double helix shape. In the end, replication produces two DNA molecules, each with one strand from the parent molecule and one new strand.
Enzymes involved in the process of DNA replication
DNA replication would not occur without enzymes that catalyze various steps in the process. Enzymes that participate in the eukaryotic DNA replication process include:
DNA helicase: unwinds and separates double stranded DNA as it moves along the DNA. It forms the replication fork by breaking hydrogen Bonds between nucleotide pairs in DNA.
DNA primase: a type of RNA polymerase that generates RNA primers. Primers are short RNA molecules that act as templates for the starting point of DNA replication.
DNA polymerases: synthesize new DNA molecules by adding nucleotides to leading and lagging DNA strands.
Topoisomerase or DNA Gyrase: unwinds and rewinds DNA strands to prevent the DNA from becoming tangled or supercoiled.
Exonucleases: group of enzymes that remove nucleotide bases from the end of a DNA chain.
DNA ligase: joins DNA fragments together by forming phosphodiester bonds between nucleotides.
RNA stands for ribonucleic acid. It is an important molecule with long chains of nucleotides. A nucleotide contains a nitrogenous base, a ribose sugar, and a phosphate. Just like DNA, RNA is vital for living beings.RNA (ribonucleic acid) is a nucleic acid polymer where the carbohydrate is ribose. RNA is generally single-stranded, as DNA is transcribed by RNA polymerases into mRNA (messenger RNA), which is read by ribosomes to generate protein (translation). Biologically active RNAs, including transport, ribosomal and small nuclear RNA (tRNA, rRNA, snRNAs) fold into unique structures guided by complementary pairing between nucleotide bases.,
DNA
Deoxyribonucleic acid (DNA) is a molecule that contains the genetic instructions for an organism. It is made up of two strands that are twisted together in a double helix shape. The order of the nucleotides in DNA determines the organism’s genetic code.
DNA is found in the nucleus of every cell in the body. It is also found in mitochondria, which are small organelles that produce energy for the cell.
DNA is responsible for storing and transmitting genetic information. It is also responsible for directing the synthesis of proteins, which are the building blocks of cells and Tissues.
DNA replication is the process by which DNA is copied so that each new cell can have its own copy of the genetic code. DNA repair is the process by which damaged DNA is repaired. DNA transcription is the process by which DNA is copied into RNA. DNA translation is the process by which RNA is used to produce proteins.
DNA mutation is a change in the DNA sequence. Mutations can be caused by errors in DNA replication, exposure to radiation or chemicals, or viruses. Some mutations are harmful, while others are beneficial.
DNA sequencing is the process of determining the order of the nucleotides in DNA. DNA cloning is the process of making multiple copies of a DNA sequence. DNA engineering is the process of modifying DNA. DNA forensics is the use of DNA to identify individuals or to solve crimes. DNA therapy is the use of DNA to treat diseases.
RNA
Ribonucleic acid (RNA) is a molecule that is similar to DNA. It is made up of nucleotides, but it has a different sugar-phosphate backbone than DNA. RNA also has a different base sequence than DNA.
RNA is found in the nucleus, cytoplasm, and mitochondria of cells. It is also found in viruses.
RNA is responsible for carrying out the instructions encoded in DNA. It is also responsible for the synthesis of proteins.
RNA transcription is the process by which DNA is copied into RNA. RNA translation is the process by which RNA is used to produce proteins.
RNA splicing is the process by which introns are removed from RNA and exons are joined together. RNA editing is the process by which the base sequence of RNA is changed. RNA interference is the process by which RNA can silence genes.
RNA viruses are viruses that have RNA as their genetic material. RNA Vaccines are vaccines that use RNA to protect against diseases. RNA therapeutics are drugs that use RNA to treat diseases.
Conclusion
DNA and RNA are two important molecules that are essential for life. DNA contains the genetic instructions for an organism, while RNA is responsible for carrying out those instructions. Both DNA and RNA are constantly being replicated, repaired, and transcribed. Mutations in DNA can cause diseases, but they can also be beneficial. DNA sequencing, cloning, engineering, forensics, and therapy are all important techniques that are used to study and manipulate DNA. RNA is also important for life, and it is involved in many different processes, including transcription, translation, splicing, editing, interference, and virus replication. RNA vaccines and RNA therapeutics are two promising new technologies that are being developed to treat diseases.
Here are some frequently asked questions and short answers about the topics of proteins, Carbohydrates, lipids, and nucleic acids:
Proteins
-
What are proteins?
Proteins are large, complex molecules that are essential for life. They are made up of amino acids, which are linked together in a chain. Proteins have a variety of functions in the body, including building and repairing tissues, transporting molecules, and catalyzing chemical reactions. -
What are the different types of proteins?
There are many different types of proteins, each with its own unique function. Some common types of proteins include enzymes, HORMONES, antibodies, and structural proteins. -
How do proteins work?
Proteins work by binding to other molecules. The specific shape of a protein determines which molecules it can bind to. This allows proteins to carry out their many different functions in the body. -
What are some examples of proteins?
Some examples of proteins include hemoglobin, which carries Oxygen in the blood; insulin, which regulates blood sugar levels; and collagen, which is a structural protein found in skin, bones, and tendons.
Carbohydrates
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What are carbohydrates?
Carbohydrates are a type of molecule that is made up of carbon, hydrogen, and oxygen. They are the body’s main Source Of Energy. Carbohydrates are found in foods such as bread, pasta, rice, potatoes, and fruits. -
What are the different types of carbohydrates?
There are three main types of carbohydrates: monosaccharides, disaccharides, and polysaccharides. Monosaccharides are the simplest type of carbohydrate. They are made up of one sugar molecule. Disaccharides are made up of two sugar molecules. Polysaccharides are made up of many sugar molecules. -
How do carbohydrates work?
Carbohydrates are broken down into glucose, which is the body’s main source of energy. Glucose is used by the cells to produce ATP, which is the energy currency of the cell. -
What are some examples of carbohydrates?
Some examples of carbohydrates include glucose, fructose, sucrose, lactose, starch, and glycogen.
Lipids
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What are lipids?
Lipids are a type of molecule that is made up of carbon, hydrogen, and oxygen. They are found in foods such as oils, fats, and cholesterol. Lipids are important for the body’s energy storage, cell membrane structure, and hormone production. -
What are the different types of lipids?
There are three main types of lipids: fats, oils, and cholesterol. Fats are solid at room temperature. Oils are liquid at room temperature. Cholesterol is a waxy substance that is found in the blood. -
How do lipids work?
Lipids are used by the body for energy storage. They are also important for the structure of cell membranes. Cholesterol is used by the body to produce hormones and vitamin D. -
What are some examples of lipids?
Some examples of lipids include triglycerides, phospholipids, and cholesterol.
Nucleic acids
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What are nucleic acids?
Nucleic acids are a type of molecule that is made up of carbon, hydrogen, oxygen, nitrogen, and phosphorus. They are found in the nucleus of cells and are responsible for storing and transmitting genetic information. -
What are the different types of nucleic acids?
There are two main types of nucleic acids: DNA and RNA. DNA is the genetic material of all living things. RNA is involved in the process of Protein Synthesis. -
How do nucleic acids work?
DNA is made up of two strands that are twisted together in a double helix shape. The order of the nucleotides on the DNA strand determines the genetic code. The genetic code is used to produce proteins. RNA is involved in the process of protein synthesis. -
What are some examples of nucleic acids?
Some examples of nucleic acids include DNA and RNA.
Here are some multiple choice questions about biology without mentioning the topic DNA and RNA:
-
Which of the following is not a type of cell?
(A) Animal cell
(B) Plant cell
(C) Prokaryotic cell
(D) Eukaryotic cell -
Which of the following is not a function of the cell membrane?
(A) Regulates the movement of substances into and out of the cell
(B) Provides support and protection for the cell
(C) Synthesizes proteins
(D) Digests food -
Which of the following is not a type of tissue?
(A) Epithelial tissue
(B) Connective tissue
(C) Muscle tissue
(D) Nervous tissue -
Which of the following is not a type of organ?
(A) Heart
(B) Lung
(C) Kidney
(D) Brain -
Which of the following is not a type of system in the human body?
(A) Circulatory System
(B) Digestive System
(C) Respiratory System
(D) Nervous system -
Which of the following is not a type of muscle in the human body?
(A) Skeletal muscle
(B) Smooth muscle
(C) Cardiac muscle
(D) Epithelial muscle -
Which of the following is not a type of bone in the human body?
(A) Long bone
(B) Short bone
(C) Flat bone
(D) Irregular bone -
Which of the following is not a type of joint in the human body?
(A) Fibrous joint
(B) Cartilaginous joint
(C) Synovial joint
(D) Epithelial joint -
Which of the following is not a type of tooth in the human body?
(A) Incisor
(B) Canine
(C) Premolar
(D) Epithelial tooth -
Which of the following is not a type of gland in the human body?
(A) Endocrine gland
(B) Exocrine gland
(C) Apocrine gland
(D) Epithelial gland -
Which of the following is not a type of vitamin in the human body?
(A) Vitamin A
(B) Vitamin B
(C) Vitamin C
(D) Epithelial vitamin -
Which of the following is not a type of mineral in the human body?
(A) Calcium
(B) Phosphorus
(C) Potassium
(D) Epithelial mineral -
Which of the following is not a type of hormone in the human body?
(A) Insulin
(B) Glucagon
(C) Estrogen
(D) Epithelial hormone -
Which of the following is not a type of enzyme in the human body?
(A) Digestive enzyme
(B) Metabolic enzyme
(C) Detoxifying enzyme
(D) Epithelial enzyme -
Which of the following is not a type of antibody in the human body?
(A) Immunoglobulin G
(B) Immunoglobulin M
(C) Immunoglobulin A
(D) Epithelial antibody -
Which of the following is not a type of white blood cell in the human body?
(A) Neutrophil
(B) Lymphocyte
(C) Monocyte
(D) Epithelial white blood cell -
Which of the following is not a type of red blood cell in the human body?
(A) Erythrocyte
(B) Leukocyte
(C) Platelet
(D) Epithelial red blood cell -
Which of the following is not a type of platelet in the human body?
(A) Thrombocyte
(B) Erythrocyte
(C) Leukocyte
(D) Epithelial platelet -
Which of the following is not a type of cancer in the human body?
(A) Carcinoma
(B) Sarcoma
(C) Leukemia
(D) Epithelial cancer -
Which of the following is not a type of virus in the human body?
(A) Coronavirus
(B) Influenza virus
(C) HIV
(D) Epithelial virus