DNA Structure - Biology

DNA nucleotides bond via hydrogen bonding to form the double helix structure. DNA is negatively charged due to the phosphates and binds to histones to form compact chromosomes in the nucleus.

RNA and DNA both have the bases cytosine, guanine and adenine in common. In RNA, uracil is present in place of thymine which is found in DNA.

DNA stands for "deoxyribonucleic acid." The backbone of DNA is comprised of alternating sugar and phosphate units, in which the sugar is deoxyribose. The backbone of RNA is also comprised of sugar and phosphate units, but uses the sugar ribose.

Nucleic acids include DNA and all forms of RNA (mRNA, tRNA, rRNA, and htRNA). Note that the different types of RNA have the same base structure, but serve different functions. Messgener RNA (mRNA) is used as the template for protein translation. Transfer RNA (tRNA) transports amino acid residues to the ribosome during translation to aid in polypeptide elongation. Ribosomal RNA (rRNA) is used to form the structure of the ribosomal subunits. Heternuclear RNA (htRNA) is the original product of transcription, and is found in the nucleus prior to post-transcriptional modifications.

Glucose is a carbohydrate, and cholesterol is a lipid.

During most of the cell cycle, DNA is found as chromatin. Chromatin is a mass of DNA and associated proteins. Depending on the state and activation of those proteins and on how tighly packed the DNA is around the proteins, certain genes can be turned on or off.

Chromosomes form from condensed chromatin only during mitosis (specifically during prophase), and are absent during most of the cell's cycle. Genes are units of heredity that encode the information needed to specify the amino acid sequence of proteins. The gene is the functional segment of DNA located at a specific place, or locus, on a chromosome. The cytoplasm is the material contained in the cell membrane and outside the nucleus. The nucleus is a membrane-bound organelle that contains the cell's genetic material.

An operon is a segment of DNA that is under the control of a single promoter. For example, if there are three genes required for breaking down a sugar in an operon, they will all be activated together. This makes sense, as there is no sense in activating only one or two of these genes, since all three are required to break down the sugar. For example, the control element that turns on the operator can be the sugar itself. It should make sense that the genes required to break down a sugar are only turned on if that sugar is present.

Genes are expressed when their gene products are made, to do this transcription and translation must occur to synthesize the protein which is coded for by the DNA.

The nucleotides in DNA always pair the same way; A with T and G with C. This is due to the chemical structure of each base; adenine and thymine form two hydrogen bonds when pairing, and guanine and cytosine form three. The other important thing to remember is that there is a different nitrogen base in RNA called uracil; uracil is not found in DNA, so pay attention to which molecule the question is asking about.

Synteny is the conservation of order of genes. Being able to see conserved blocks in genes when comparing two chromosomes of the same species, it indicates that at some time in evolutionary history, these blocks originated from a hypothetical common ancestor. Genes that are highly conserved among species are usually vital to the organism's viability. For example, the genes required for glycolysis to occur are required in almost all organisms.

The human genome can be described as a chain of nucleotides that is 3.2 billion base pairs long. Twenty-three different lengths that are called chromosomes segment this string of material. Genes further segment the chromosomes. The chromosomes vary in length and so do their genes. DNA of a gene on a certain part of a certain chromosome can be transcribed into mRNA, which is then translated into protein. The number of genes in our genome has been highly contested. It was originally believed that humans had over 100,000 genes. This number declined as we learned more about our genome and was more or less standardized to be around 25,000 upon completion of the Human Genome Project.

A chromosome is one molecule of DNA. It contains genetic information required for cell replication and the passing down of genetic information. Humans have 23 pairs of chromosomes, with one chromosome per pair from the mother, and the other from the father.

Humans have 23 homologous pairs of chromosomes, which adds up to 46 chromosomes total. Diploid cells have two copies of each chromosome (one from the mother, one from the father). A gamete is haploid, meaning it only contains one copy of each chromosome. The gametes (haploid) will fuse in a process known as fertilization in order to form a diploid zygote.

An allele is a variant or alternative form of a gene or gene locus. Humans are diploid—we have two alleles at each genetic locus. One allele is inherited from the mother and one allele comes from the father. Sometimes different alleles can lead to different phenotypic traits (e.g. eye color); however, most genetic variations result in little to no observable variation. An organism is considered homozygous if it possesses two of the same alleles at a particular locus. If the alleles are different, then the organism is considered heterozygous.

DNA—deoxyribonucleic acid—is found in chromosomes within a cell’s nucleus. A complete set of DNA (i.e. 46 chromosomes) is called a genome. DNA contains instructions that make humans different from other species and other individuals. DNA provides instructions for all the proteins that the body makes and is passed from adults to offspring. DNA cannot get out of the nucleus; however, RNA can. RNA is used to get the instructions from DNA out of the nucleus and into the site of protein synthesis: the ribosomes within the cytoplasm. Proteins are made of amino acids and determine the structure and function of all of the body’s cells.

Based on the definition of genome, it is the entire set of DNA found within all the chromosomes an organism contains. The human genome is contained on 23 pairs of chromosomes, which code for about 25,000 genes.

When determining the complementary strand, remember that it will be written in the opposite direction of the template strand. This means that the new strand's 5' end will begin at the 3' end of the template strand. The complementary strand will also be composed of the nucleotides that complete the base pairs found in DNA (A-T and C-G).

Template: 5'-GCCTCATGA-3'

Answer: 5'-TCATGAGGC-3'

To see these pairs match up, the 3' end of the answer must align with the 5' end of the template.

Template: 5'-GCCTCATGA-3'

Answer (3'-5'): 3'-CGGAGTACT-5'

There are two classes of bases in DNA and RNA: purines and pyrimidines. The difference between these classes is the structure of the base. Purines have two rings in their structure, while pyrimidines have only one. Purines will pair with pyrimidines.

The purines are adenine and guanine, and the pyrimidines are thymine, cytosine, and uracil. You can remember that the bases that contain a "y" are pyrimidines (thymine and cytosine).

There are four bases in DNA: adenine, thymine, guanine, and cytosine. Adenine always pairs with thymine, so the number of adenine residues always equals the number of thymine residues. Guanine always pairs with cytosine, which means they are always present in equal amounts as well. If one strand contains three cytosine bases and five thymine bases, then the opposite strand must contain three guanine bases and five adenine bases.

The trick to this problem is remembering that the sum of all four bases by percentage must be 100%.

We know that 30% of the bases are cytosine. Since cytosine pairs with guanine, there is also 30% guanine.

That leave us with 40% of the bases being thymine and adenine.

Since adenine and thymine will be equal, each will represent 20% of the DNA composition.

There are four nitrogenous bases in DNA: adenine, guanine, cytosine, and thymine. A nucleotide is composed of one of these bases bound to a deoxyribose sugar and a phosphate group. Polymers of nucleotides form strands of DNA, which adhere to one another by hydrogen bonding between the bases.

Each strand of DNA is unique and may contain any ratio of the nitrogenous bases, but strands of DNA will always be complementary to one another. The structure of the bases requires that adenine bind to thymine and cytosine bind to guanine to maintain the structural integrity of the DNA molecule. RNA does not contain thymine, and instead uses uracil.