Molecular Biology-Study Guide

Nucleotides

A nitrogenous base, which can be either adenine, guanine, cytosine, or thymine (in the case of RNA, thymine is replaced by uracil). A five-carbon sugar, called deoxyribose because it is lacking an oxygen group on one of its carbons.One or more phosphate groups.

Phosphates

A phosphate group consists of a central phosphorous surrounded by four oxygens.

Nucleic Acids

Nucleotides join together through phosphodiester linkages between the 5' and 3' carbon atoms to form nucleic acids. The 3' -OH of the sugar group forms a bond with one of the negatively charged oxygens of the phosphate group attached to the 5' carbon of another sugar.

Cell Reproduction

Prokaryotic cells such as bacterial cells reproduce by binary fission, a process that includes DNA replication, chromosome segregation, and cytokinesis. Eukaryotic cell division either involves mitosis or a more complex process called meiosis.

Differences Between DNA and RNA

RNA Differences Between DNA and RNA Structurally, DNA and RNA are nearly identical. RNA is a single-stranded nucleic acid. RNA has a ribose sugar instead of a deoxyribose sugar like DNA. RNA nucleotides have a uracil base instead of thymine. Other than these differences, DNA and RNA are the same. Their phosphates, sugars, and bases show the same bonding patterns to form nucleotides and their nucleotides bind to form nucleic acids in the same way.

The Cell Cycle

The cell cycle or cell-division cycle is the series of events that take place in a cell leading to its division and duplication of its DNA to produce two daughter cells.

The Deoxyribose Sugar

The deoxyribose sugar in DNA is a pentose, a five-carbon sugar. Four carbons and an oxygen make up the five-membered ring; the other carbon branches off the ring. Similar to the numbering of the purine and pyrimidine rings (seen in ), the carbon constituents of the sugar ring are numbered 1'-4' (pronounced "one-prime carbon"), starting with the carbon to the right of the oxygen going clockwise (). The fifth carbon (5') branches from the 4' carbon.

The Bases of DNA

The four nitrogen bases found in DNA are adenine, cytosine, guanine, and thymine. Each of these bases are often abbreviated a single letter: A (adenine), C (cytosine), G (guanine), T (thymine). The bases come in two categories: thymine and cytosine are pyrimidines, while adenine and guanine are purines ().

Base Pairing in DNA

The nitrogen bases form the double-strand of DNA through weak hydrogen bonds. The nitrogen bases, however, have specific shapes and hydrogen bond properties so that guanine and cytosine only bond with each other, while adenine and thymine also bond exclusively. This pairing off of the nitrogen bases is called complementarity. In order for hydrogen bonding to occur at all, a hydrogen bond donor must have a complementary hydrogen bond acceptor in the base across from it. Common hydrogen bond donors include primary and secondary amine groups or hydroxyl groups. Common acceptor groups are carbonyls and tertiary amines ().

The Ribose Sugar

The ribose sugar is structurally identical to the deoxyribose sugar, with the addition of a hydroxyl group at the 2' position ().

The Uracil Base

The uracil base replaces thymine in RNA. Thymine and uracil are structurally very similar.

Chromosome

a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.

Meiosis

a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.

Mitosis

a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus, typical of ordinary tissue growth.

Karyotype

the number and visual appearance of the chromosomes in the cell nuclei of an organism or species.

Genetics

the study of heredity and the variation of inherited characteristics.