What is the relationship between nucleotides genes chromosomes amino acids codons and proteins

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Most genes contain the information needed to make functional molecules called proteins. (A few genes produce regulatory molecules that help the cell assemble proteins.) The journey from gene to protein is complex and tightly controlled within each cell. It consists of two major steps: transcription and translation. Together, transcription and translation are known as gene expression.

During the process of transcription, the information stored in a gene's DNA is passed to a similar molecule called RNA (ribonucleic acid) in the cell nucleus. Both RNA and DNA are made up of a chain of building blocks called nucleotides, but they have slightly different chemical properties. The type of RNA that contains the information for making a protein is called messenger RNA (mRNA) because it carries the information, or message, from the DNA out of the nucleus into the cytoplasm.

Translation, the second step in getting from a gene to a protein, takes place in the cytoplasm. The mRNA interacts with a specialized complex called a ribosome, which "reads" the sequence of mRNA nucleotides. Each sequence of three nucleotides, called a codon, usually codes for one particular amino acid. (Amino acids are the building blocks of proteins.) A type of RNA called transfer RNA (tRNA) assembles the protein, one amino acid at a time. Protein assembly continues until the ribosome encounters a “stop” codon (a sequence of three nucleotides that does not code for an amino acid).

The flow of information from DNA to RNA to proteins is one of the fundamental principles of molecular biology. It is so important that it is sometimes called the “central dogma.”

To prevent mistakes during replication, cells have a “proofreading” function to help ensure that bases are paired properly. There are also chemical mechanisms to repair DNA that was not copied properly. However, because of the billions of base pairs involved in, and the complexity of, the protein synthesis process, mistakes may happen. Such mistakes may occur for numerous reasons (including exposure to radiation, drugs, or viruses) or for no apparent reason. Minor variations in DNA are very common and occur in most people. Most variations do not affect subsequent copies of the gene. Mistakes that are duplicated in subsequent copies are called mutations.

Inherited mutations are those that may be passed on to offspring. Mutations can be inherited only when they affect the reproductive cells (sperm or egg). Mutations that do not affect reproductive cells affect the descendants of the mutated cell (for example, becoming a cancer) but are not passed on to offspring.

Mutations may be unique to an individual or family, and most harmful mutations are rare. Mutations that become so common that they affect more than 1% of a population are called polymorphisms (for example, the human blood types A, B, AB, and O). Most polymorphisms have little or no effect on the phenotype (the actual structure and function of a person’s body).

Mutations may involve small or large segments of DNA. Depending on its size and location, the mutation may have no apparent effect or it may alter the amino acid sequence in a protein or decrease the amount of protein produced. If the protein has a different amino acid sequence, it may function differently or not at all. An absent or nonfunctioning protein is often harmful or fatal. For example, in phenylketonuria Phenylketonuria (PKU) Phenylketonuria is a disorder of amino acid metabolism that occurs in infants born without the ability to normally break down an amino acid called phenylalanine. Phenylalanine, which is toxic... read more , a mutation results in the deficiency or absence of the enzyme phenylalanine hydroxylase. This deficiency allows the amino acid phenylalanine (absorbed from the diet) to accumulate in the body, ultimately causing severe intellectual disability. In rare cases, a mutation introduces a change that is advantageous. For example, in the case of the sickle cell gene, when a person inherits two copies of the abnormal gene, the person will develop sickle cell disease Sickle Cell Disease Sickle cell disease is an inherited genetic abnormality of hemoglobin (the oxygen-carrying protein found in red blood cells) characterized by sickle (crescent)-shaped red blood cells and chronic... read more

Natural selection refers to the concept that mutations that impair survival in a given environment are less likely to be passed on to offspring (and thus become less common in the population), whereas mutations that improve survival progressively become more common. Thus, beneficial mutations, although initially rare, eventually become common. The slow changes that occur over time caused by mutations and natural selection in an interbreeding population collectively are called evolution.

A gene is a basic unit of heredity in a living organism that normally resides in long strands of DNA called chromosomes. Genes are coded instructions that decide what the organism is like, how it behaves in its environment and how it survives. They hold the information to build and maintain an organism’s cells and pass genetic traits to offspring. A gene consists of a long combination of four different nucleotide bases namely adenine, cytosine, guanine and thymine. All living things depend on genes as they specify all proteins and functional RNA chains.

What are Proteins?

Proteins are large, complex molecules that play many critical roles in the body. They are necessary for building the structural components of the human body, such as muscles and organs. Proteins also determine how the organism looks, how well its body metabolises food or fights infection and sometimes even how it behaves. Proteins are chains of chemical building blocks called amino acids. A protein may contain a few amino acids or it could have several thousands. The size of a protein is an important physical characteristic that provides useful information including changes in conformation, aggregation state and denaturation. Protein scientists often use particle size analysers in their studies to discuss protein size or molecular weight.

Archibald Garrod

Archibald Garrod was one of the first scientists to propose that genes controlled the function of proteins. In 1902, he published his observations regarding patients whose urine turned black. This condition known as alkaptonuria happens when there is a buildup of the chemical homogentisate, which causes the darkening of urine. In most situations, excess amounts of amino acid phenylalanine are metabolised by the body. This led Garrod to surmise that the enzyme responsible for its breakdown must be defective in these patients. In addition, since the black urine phenotype was passed from generation to generation in a regular pattern, Garrod reasoned that a gene had to be responsible for the production of the defective enzyme. He attributed a defective enzyme to a defective gene, suggesting a direct link between genes and proteins.

The Relationship Between Genes and Proteins

Most genes contain the information require to make proteins. The journey from gene to protein is one that is complex and controlled within each cell and it consists of two major steps – transcription and translation. Together, these two steps are known as gene expression.

Transcription: Information stored in a gene’s DNA is transferred to a similar molecule called RNA in the cell nucleus. Although both DNA and RNA are made up of a chain of nucleotide bases, they have slightly different chemical properties. The type of RNA that contains the information needed to make protein is called a messenger RNA or mRNA and it carries the message from the DNA out of the nucleus into the cytoplasm.

Translation: This is the second step in the production of proteins and it takes place in the cytoplasm. The mRNA interacts with a specialised complex known as a ribosome that reads the sequence of the mRNA bases. Each sequence has three bases called a codon, which codes for one particular amino acid. A transfer RNA or tRNA assembles the protein, one amino acid at a time. This continues until the ribosome meets a “stop” codon. The characterisation of different proteins can be conducted by Size Exclusion Chromatography as this technique can be used characterise molecular weight, structure and aggregation state.

Learn more about genes and proteins

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