What makes the backbone of dna and rna

These sugars are linked together by a phosphodiester bond , between carbon 4 of their chain, and a CH 2 group that is attached to a phosphate ion. They are extremely important in the function of DNA. Figure 1 Diagram showing the sugar phosphate backbone of DNA, and the nitrogenous bases attached to it, forming a nucleotide [1].

DNA is wound into an right-handed double helix. The strands are anti-parellel i. Each strand has a backbone made of alternating sugar deoxyribose and phosphate groups. Attached to each sugar is one of four bases--adenine A , cytosine C , guanine G , or thymine T.

The two strands are held together by bonds between the bases, with adenine forming a base pair with thymine, and cytosine forming a base pair with guanine. An RNA molecule is said to be monocistronic when it captures the genetic information for a single molecular transcriptional product, e. Most eukaryotic mRNAs are indeed monocistronic. In the case of polycistronic mRNAs, the primary transcript comprises several back-to-back mRNAs, each of which will be eventually translated into an amino acid sequence polypeptide.

Such polypeptides usually have a related function they often are the subunits composing a final complex protein and their coding sequences are grouped into a single primary transcript, which in turn permits them to share a common promoter and to be regulated together. MRNAs carry the genetic information that directs the synthesis of proteins by the ribosomes. All cellular organisms use mRNAs.

The structure of an mRNA. RNA interference is a process that moderates gene expression in a sequence dependent manner. The RNAi pathway is found in all higher eukaryotes and was recently found in the budding yeast as well.

SiRNAs are double-stranded ncRNAs that are mainly delivered to the cell experimentally by various transfection methods although they have been described to be produced form the cell itself SiRNAs are typically designed to be perfectly complementary to their targets.

RNA interference in mammalian cells. Designer siRNAs are now widely used in the laboratory to down-regulate specific proteins whose function is under study. At the same time, the ability to engage the RNAi pathway in an on demand manner suggests the possibility that RNAi can be used in the clinic to reduce the production of those proteins that are over-expressed in a given disease context. The delivery method remains an important consideration for the development of RNAi-based therapies as the active molecule needs to be delivered efficiently and in a tissue-specific manner in order to maximize impact and diminish off-target effects.

See also: RNAi external link. The expression of proteins is determined by genomic information, and their presence supports the function of cell life.

Things began to change with the discovery of microRNAs more than 20 years ago in plants 16 and animals 17 , These RNA transcripts have been referred to as ncRNAs and there is increased appreciation that many of them are indeed functional and affect key cellular processes.

There are many recognizable classes of ncRNAs, each having a distinct functionality. The full extent of distinct classes of ncRNAs that are encoded within the human genome is currently unknown but are believed to be numerous. The biological role of long ncRNAs as a class remains largely elusive. Several specific cases have been shown to be involved in transcriptional gene silencing, and the activation of critical regulators of development and differentiation: these exerted their regulatory roles by interfering with transcription factors or their co-activators, though direct action on DNA duplex, by regulating adjacent protein-coding gene expression, by mediating DNA epigenetic modifications, etc.

This is known to occur in the case of retroviruses, such as HIV, as well as in eukaryotes, in the case of retrotransposons and telomere synthesis. Post-transcriptional modification is a process in cell biology by which, primary transcript RNA is converted into mature RNA. This process is vital for the correct translation of the genomes of eukaryotes as the human primary RNA transcript that is produced as a result of transcription contains both exons, which are coding sections of the primary RNA transcript and introns, which are the non coding sections of the primary RNA transcript.

The cap and tail protect the mRNA from enzyme degradation and aid its attachment to the ribosome. In addition, iii introns non-coding sequences are spliced out of the mRNA and exons coding sequences are spliced together. The mature mRNA transcript will then undergo translation A protein is a molecule that performs reactions necessary to sustain the life of an organism.

One cell can contain thousands of proteins. Following transcription, translation is the next step of protein biosynthesis. In translation, mRNA produced by transcription is decoded by the ribosome to produce a specific amino acid chain, or a polypeptide, that will later fold into a protein. Ribosomes read mRNA sequence in a ticker tape fashion three bases at a time, inserting the appropriate amino acid encoded by each three-base code word or codon into the appropriate position of the growing protein chain.

This process is called mRNA translation. Each amino acid is encoded by a sequence of three successive bases. Some specialized codons serve as punctuation points during translation. The methionine codon AUG , serves as the initiator codon signaling the first amino acid to be incorporated. All proteins thus begin with a methionine residue, but this is often removed later in the translational process.

The completed polypeptide chain then folds into a functional three-dimensional protein molecule and is transferred to other organelles for further processing or released into cytosol for association of the newly completed chain with other subunits to form complex multimeric proteins.

Protein translation. Post-translational modification is the chemical modification of a peptide that takes place after its translation. They represent one of the later steps in protein biosynthesis for many proteins.

During protein synthesis, 20 different amino acids can be incorporated in order to form a polypeptide. In addition, enzymes may remove amino acids from the amino end of the protein, or even cut the peptide chain in the middle.

This amino acid is usually taken off during post-translational modification. Other modifications, like phosphorylation, are part of common mechanisms for controlling the behavior of a protein, for instance activating or inactivating an enzyme. See also: Inside a cell external link.

Home Learn! DNA 1. DNA transcription 1. Regions of DNA in the human genome, ranging from 0. Approximately half of all gene promoters have CpG islands that when methylated lead to transcriptional silencing. Aberrant DNA methylation patterns have been described in various human malignancies. Do you want to LearnCast this session? This article has been posted to your Facebook page via Scitable LearnCast. Change LearnCast Settings.

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