DNA - Biology

DNA helicase unwinds the double helix, separating the two strands so they may be replicated by DNA polymerase.

Primase adds an RNA primer to help initiate DNA replication. DNA ligase is responsible for joining Okazaki fragments on the lagging strand during replication.

DNA replication is the process of copying the parent DNA helix into two identical daughter helices. The process is semi-conservative, which means that one parent strand is passed down to each daughter strand. The process begins when helicase unwinds the double helix and separates the two strands to create the replication fork. Topoisomerase helps this process by relieving rotational strain on the helix when it is being unwound. DNA polymerase adds new nucleotides to the daughter strand, synthesizing the new DNA strand.

During replication there is a leading strand, which occurs when replication occurs from 5' to 3' and moves towards the replication fork, and a lagging strand, when replication occurs away from the replication fork. Replication occurs in short segments on the lagging strand, known as Okazaki fragments. The protein DNA ligase is responsible for finally fusing these fragments together after they are made by DNA polymerase.

The question states that DNA helicase "unzips" the two strands of DNA; therefore, this enzyme must be breaking down the bonds between base pairs.

The bonds between base pairs are called hydrogen bonds, which is a noncovalent bond. This means that the DNA helicase is breaking down the hydrogen bonds between base pairs in order to separate the two strands. In DNA, there are two kinds of base pairs: purines and pyrimidines. Recall that adenine and guanine are classified as purines whereas thymine and cytosine are classified as pyrimidines; therefore, a base pairing in DNA always occurs between a purine and a pyrimidine. This means that the DNA helicase is breaking down the hydrogen bonds between purines and pyrimidines.

DNA ligase is the protein responsible for linking, or ligating, Okazaki fragments together in order to form a single complete DNA strand. This action only necessary on the lagging strand; the leading strand can be made continuously by DNA polymerase since it is able to read away from the replication fork in the 3'-to5' direction. Since the DNA polymerase on the lagging strand must read toward the replication form, it cannot by synthesized continuously.

Helicase is the protein resposible for unwinding the DNA double-helix. Single-strand binding proteins attach to the freshly unwound strands of DNA and ensure that the strands do not re-anneal. Helicase creates the replication fork opening, allowing replication proteins to enter and bind; single-strand binding proteins keep the replication fork open as proteins enter.

A DNA fragment will be formed in the 5' to 3' direction because of the polarity of the DNA molecule. Adding nucleotides to the 3' end allows DNA polymerase to use the phosphate molecules as "fuel," and add a new nucleotide to the DNA strand.

DNA Polymerase I removes the primer from the 5' end of a lagging strand, and replaces it with DNA nucleotides. This allows DNA synthesis to begin on the lagging strand.

Guanine - cytosine and adenine - thymine form "complimentary base pairs." Guanine can only form hydrogen bonds with cytosine and adenine can only form hydrogen bonds with thymine (and vice versa). With that in mind, any base pairing other than those two can be excluded from this answer. Furthermore, cytosine and guanine form a total of three hydrogen bonds together while adenine and thymine only form two. The extra bond between guanine and cytosine makes the pairing about 50% stronger.

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.

A nucleotide is the building block of nucleic acids (a type of macromolecule). It is made up of three main parts: phosphate group(s), pentose sugar, and a nitrogenous base (adenine, thymine, guanine, cytosine, or uracil). The amount of phosphate groups, the type of pentose sugar, and the type of nitrogenous base varies based on the nucleotide. For example, RNA contains ribose sugar whereas DNA contains deoxyribose sugar.

Arginine is a type of amino acid. Recall that amino acids are found in polypeptide chains that make up proteins (another type of macromolecule); therefore, arginine is found in proteins rather than nucleic acids.

The main difference between a nucleotide and a nucleoside is the presence or absence of phosphate group(s). A nucleotide contains one or more phosphate groups, a pentose sugar, and a nitrogenous base. A nucleoside, on the other hand, contains only a pentose sugar and a nitrogenous base; therefore, a nucleotide always contains more phosphate groups than a nucleoside.

NADH is a coenzyme that functions to carry electrons during metabolism. It is made up of adenine (a nitrogenous base), nicotinamide (a modified nitrogenous base), two phosphate groups, and two pentose sugars. Since it contains nitrogenous bases, phosphate groups, and pentose sugars it is a type of nucleotide.

cAMP, or cyclic adenosine monophosphate, is a second messenger molecule that facilitates signal transduction inside the cell. It is made up of adenine, a phosphate group, and a pentose sugar (ribose); therefore, it is also a type of nucleotide.

Acetylcholine is a type of neurotransmitter that plays a key role in signal transmission between neurons. Acetylcholine does not contain the three essential groups for a nucleotide; therefore, acetylcholine is not a nucleotide.

To answer this question you need to know the difference between a nucleotide and a DNA backbone. A nucleotide is the monomer of nucleic acids and is made up of phosphate group(s), a pentose sugar, and a nitrogenous base. A DNA molecule is a type of nucleic acid and is made up of several nucleotides.

DNA has two different structural divisions: the DNA backbone and the nitrogenous bases. The DNA backbone consists of the phosphate groups and pentose sugars, whereas the bases consist of only the nitrogenous bases. This means that the DNA backbone does not contain any nitrogenous bases; therefore, nucleotide contains more nitrogenous bases than the DNA backbone.

Since the full DNA molecules has several nucleotides, the DNA backbone contains multiple phosphate groups and pentose sugars; therefore, the DNA backbone always contains more phosphate groups and pentose sugars than a nucleotide molecule.

The four nitrogenous bases found in DNA are: thymine, cytosine, adenine, and guanine. Uracil is a nitrogenous base that takes the place of thymine in RNA. Note that uracil only base pairs with adenine, forming two hydrogen bonds.

Guanine always binds to cytosine in DNA and RNA. Thymine always bonds to adenine in DNA. Uracil replaces thymine in RNA, and uracil bonds to adenine.

Adenine and guanine are the purines that bond to the pyrimidines. Cytosine and thymine are the pyrimidines. The purines consist of two carbon rings, and the pyrimidines consist of one carbon ring.

DNA contains four nitrogen bases: adenine, thiamine, guanine and cytosine. Adenine and thymine pair, and guanine and cytosine pair. Adenine and thiamine form two hydrogen bonds, and guanine and cytosine form three hydrogen bonds. In RNA, uracil takes thiamine's and binds with adenine.