• New Clinical Genetics 3rd Edition
• New Clinical Genetics 3rd Edition Free Pdf
• New Clinical Genetics 3rd Edition Ebook

AbstractProteins are made of chains of amino acids and form the largest organic component of the human body. They are essential not only to its fabric but also to its functioning. Instructions for building proteins are contained in the genetic code stored in deoxyribonucleic acid (DNA) in the nucleus of cells. To go from genes to proteins, a series of complex processes need to take place inside cells, including DNA transcription and translation.

This third article in our examines how the genetic code stored in human genes is translated into proteins. It also explains how errors in the genetic code, or mutations, can lead to the production of abnormal proteins that may cause disease.Citation: Knight J, Andrade M (2018) Genes and chromosomes 3: genes, proteins and mutations. Nursing Times online; 114: 9, 60-64.Authors: John Knight and Maria Andrade are both senior lecturers in biomedical science at the College of Human Health and Science, Swansea University. This article has been double-blind peer reviewed. Scroll down to read the article or (if the PDF fails to fully download please try again using a different browser). to see other articles in this seriesIntroductionThe blueprint for constructing and operating the human body is stored in sequences of deoxyribonucleic acid (DNA) called genes. This genetic information is used to make proteins with different functions, from structural proteins essential for building muscle, bone and skin to enzymes that catalyse the biochemical reactions essential to the body’s survival.

Ursus trotter aspiradora panzaer 1420. Errors in the human genetic code, which are called mutations, sometimes lead to the production of abnormal proteins that may cause disease, including autoimmune disease and malignancy. ProteinsProteins are essential to both the fabric and function of the human body.

These complex macromolecules are constructed from building blocks called amino acids, simple organic compounds containing a carboxyl (-COOH) and an amino (-NH2) group. There are 20 naturally occurring amino acids (Box 1); other variants can be produced synthetically in the laboratory.

The 20 naturally occurring amino acidsEssential amino acids. Histidine. Isoleucine. Leucine. Lysine. Methionine.

Phenylalanine. Threonine. Tryptophan.

ValineNon-essential amino acids. Alanine. Arginine. Asparagine.

Aspartic acid. Cysteine. Glutamine.

Glutamic acid. Glycine. Proline.

Serine. TyrosineAmino acidsTo function efficiently, human cells need to continually build new proteins to replace older, damaged ones. This requires a steady supply of all 20 amino acids. During digestion, the gastrointestinal tract sequentially breaks down the large animal and plant proteins contained in food into polypeptides, peptides and eventually into ‘free’ amino acids that are able to cross the gut wall to be absorbed into the bloodstream (VanPutte et al, 2017).Naturally occurring amino acids (Box 1) are split into two categories. Essential – the nine amino acids that human cells canot synthesise and so need to obtain directly from food;. Non-essential – the 11 amino acids that human cells can synthesise if direct supply through diet is low.This terminology can be confusing, as so-called non-essential amino acids are actually essential for building proteins; the term is merely used to denote the fact that they do not have to be obtained from dietary intake.If adequate nutrition is maintained through a healthy and balanced diet, cells receive the amino acids required for protein turnover.

However, poor diet, eating disorders, certain medications and the ageing process (which can reduce appetite) can all restrict the dietary availability of amino acids, particularly the nine essential ones. This compromises the body’s ability to replace proteins, potentially resulting in muscle wastage and disease. Protein varietiesProteins form the largest organic component of the human body, making up approximately 50% of the dry mass of a typical human cell (Radivojac, 2013).

They are synthesised in the cytoplasm of cells, where amino acids are linked together by peptide bonds to form long branching chains that range from a few amino acids to thousands. These amino acid chains further fold or twist into the unique three-dimensional configurations they need to adopt to fulfil their designated roles in the body (VanPutte et al, 2017).The largest currently known protein in the human body is a muscle protein called titin (or connectin), which consists of around 33,000 amino acids. It works as a molecular spring and is thought to contribute to the force of muscle contraction (Powers et al, 2014).The human genome project has shown that humans have just under 20,000 structural genes encoding for individual proteins. Complementary base pairing rulesIn DNA replication (DNA to DNA). Adenine always pairs with thymine (A-T).

New Clinical Genetics 3rd Edition

Cytosine always pairs with guanine (C-G)In DNA transcription (DNA to mRNA). Adenine always pairs with uracil (A-U). Guanine always pairs with cytosine (G-C). Thymine always pairs with adenine (T-A).

Cytosine always pairs with guanine (C-G)DNA = deoxyribonucleic acid. Post-transcriptional modificationsNot all information encoded in mRNA strands is useful for constructing a protein.

A newly transcribed RNA strand consists of two elements:. Exons – sequences of essential information for building a protein that has the correct sequence of amino acids;. Introns – sequences that interrupt the exon coding sequences and do not usually hold useful information for building a protein. Once considered junk sequences, introns are now thought to play a role in regulating gene expression (Chorev and Carmel, 2012).The introns need to be cut out and the exons spliced together to form a contiguous ‘high-fidelity’ mRNA sequence: this cutting and splicing – called post-transcriptional modification – is done by enzymes in the nucleus. The process is shown in Fig 2.

Nature of the genetic codeThe genetic code is a triplet of three nitrogenous bases coding for one amino acid. As there are 20 naturally occurring amino acids, three bases allow for each amino acid to be represented by one triplet code (and some are represented more than once). The triplet code also allows ‘start-and-stop’ instructions to be encoded into the mRNA strand, so ribosomes know when to begin and when to end the construction of a protein.Each run of three bases (triplet code) on an mRNA strand is called a codon. The first codon on any mRNA strand is always the ‘start’ codon – called AUG – which instructs the ribosome to begin protein synthesis. Since AUG also codes for the amino acid methionine, methionine is the first amino acid incorporated into a protein – if it is not actually needed, it will be removed later (Xiao et al, 2010).The amino acids themselves are delivered to the ribosomes by transfer RNA (tRNA) molecules.

A unique tRNA molecule corresponds to each amino acid and each tRNA molecule has its own unique triplet code, which corresponds to a codon on the mRNA strand. These tRNA sequences complement the mRNA codons and are therefore called anticodons (VanPutte et al, 2017). TranslationAfter transcription and post-transcriptional modification, a mature, uninterrupted sequence of mRNA is generated. Post-translational modificationsThe crude protein usually needs to be modified before it can adopt its final 3D configuration and start performing its function in the body. References:Chorev M, Carmel L (2012) The function of introns.

Frontiers in Genetics; 3: 55.Cooper DN et al (2010) Genes, mutations, and human inherited disease at the dawn of the age of personalized genomics. Human Mutation; 31: 6, 631-655.De la Cruz J et al (2015) Functions of ribosomal proteins in assembly of eukaryotic ribosomes in vivo. Annual Review of Biochemistry; 84: 93-129.Green AC, Williams GM (2007) Point: sunscreen use is a safe and effective approach to skin cancer prevention. Cancer Epidemiology, Biomarkers and Prevention; 16: 10, 1921-1922.Hopkins R (2015).

SciBytes.Huang S, Wang Y (2017) Golgi structure formation, function, and post-translational modifications in mammalian cells. F1000 Research; 6: 2050.Lewis R (2018) Human Genetics: Concepts and Applications. New York, NY: McGraw-Hill Education.Ponomarenko EA et al (2016) The size of the human proteome: the width and depth. International Journal of Analytical Chemistry; doi: 10.1155/20.Powers K et al (2014) Titin force is enhanced in actively stretched skeletal muscle. Journal of Experimental Biology; 217: 3629-3636.Radivojac P (2013).VanPutte CL et al (2017) Seeley’s Anatomy and Physiology. New York, NY: McGraw-Hill Education.Vipond K (2013) Genetics: A Guide for Students and Practitioners of Nursing and Health Care. Banbury: Lantern Publishing.Xiao Q et al (2010) Protein N-terminal processing: substrate specificity of Escherichia coli and human methionine aminopeptidases.

New Clinical Genetics 3rd Edition Free Pdf

New Clinical Genetics 3rd Edition Ebook

Biochemistry; 49: 26, 5588-5599.