Nucleic Acids, DNA, RNA, and Cell Division: Key Concepts
What are Nucleic Acids?
Nucleic acids are long molecules formed by the union of simpler molecules called nucleotides.
Components of a Nucleotide
A nucleotide is composed of:
- A nitrogenous base: There are five different bases:
- Adenine (A)
- Guanine (G)
- Cytosine (C)
- Thymine (T)
- Uracil (U)
- A five-carbon sugar (pentose), which can be ribose or a derivative of it called deoxyribose.
- A phosphate group, which is a derivative of phosphoric acid (H3PO4).
Similarities and Differences Between RNA and DNA
| RNA | DNA |
|---|---|
Located in the nucleus and the cytoplasm of cells. | Found in the nuclei of eukaryotic cells and in the cytoplasm of prokaryotic cells. |
Contains ribose, and is formed by A, G, C, and U. | Contains deoxyribose, and is formed by A, G, C, and T. |
Generally comprises a single chain of nucleotides. | Is made up of two chains of deoxyribonucleotides. |
Several types of RNA, such as messenger RNA (mRNA) and transfer RNA (tRNA), are involved in protein synthesis. |
Different Types of Chromosomes
Chromosomes are classified based on the position of the centromere:
- Metacentric: Centromere is located in the middle of the chromosome.
- Submetacentric: Centromere is further to one side.
- Acrocentric: Centromere is very near one of the ends of the chromosome.
- Telocentric: Centromere is at the end of the chromosome.
Chromosome Number in Organisms
- Diploid organisms: They have two sets of n chromosomes, or 2n chromosomes.
- Haploid organisms: One cell has a single set of chromosomes, or n chromosomes.
Function of Nucleic Acids
Nucleic acids regulate a cell’s activity and transfer genetic information to its descendants.
Chromosome vs. Chromatid
Chromosomes are structures formed by the condensation of chromatin during cell division. Chromatids are fibers resulting from the replication of chromatin, joined together at a point called the centromere, and form chromosomes.
What is a Protein?
Proteins are large molecules created by smaller molecules (amino acids) linking together to form a chain. Proteins perform many important cell functions.
Purpose of Transcription and Translation
The main purpose of transcription and translation is protein synthesis.
What is a Codon?
A codon is a triplet of nucleotides in messenger RNA (mRNA).
Roles of mRNA and tRNA in Protein Synthesis
mRNA transports the genetic information from DNA to ribosomes. tRNA transports amino acids to the ribosomes for protein assembly.
What is Genetic Code?
The genetic code is the correspondence between mRNA codons and the amino acids that form proteins.
Main Characteristics of the Genetic Code
- It is universal.
- It is degenerate, meaning that most amino acids have more than one corresponding codon.
- It has termination codons.
- It starts with a codon AUG.
What is DNA Replication?
DNA replication is the process by which an identical copy of each of the strands that form DNA is made.
What is Cell Division?
Cell division is a process in which two daughter cells, containing the same genetic information as the parent cell, are created.
Differences Between Mitosis and Meiosis
| Mitosis | Meiosis |
|---|---|
Occurs in somatic cells | Occurs in germ cells |
Occurs in haploid and diploid cells | Occurs in diploid cells |
Nucleus divides once | Nucleus divides twice |
No crossover, produces two daughter cells | Crossover occurs, produces four daughter cells |
Cell Division in Mitosis
Prophase: The nuclear membrane and nucleolus disappear. The centrioles separate and move to opposite poles of the cell.
Metaphase: Chromosomes reach maximum condensation. The spindle apparatus drags the chromosomes to the equatorial plate.
Anaphase: Chromatids separate. Spindle filaments become shorter.
Telophase: Chromosomes decondense. The nuclear membrane and nucleolus reform. The spindle apparatus disappears. Two nuclei are formed, each with a 2n genetic makeup.