Heredity and Gene Expression

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Learning Objectives

  1. Understand the structure of DNA and how it functions in complementary base pairing.
  2. Understand Central Dogma (replication, transcription, translation).
  3. Understand gene structure (promoter, exons, introns).
  4. Compare and contrast DNA and RNA.

Solutions

  1. DNA has three functional structural components: a nitrogenous base (adenine, cytosine, guanine, and thymine), a 5-carbon sugar (in DNA, it's deoxyribose), and a phosphate group. The nitrogenous bases, as the name suggests, are what is important in complementary base pairing. Adenine will only pair with thymine, and cytosine will only pair with guanine. Adenine and guanine have two rings, called purines. Cytosine and thymine have one single ring, called pyramindines. The only amount of rings any one base pair can have is two rings, so a pryamidine must pair with a purine. In addition, adenine and thymine can form two hydrogen bonds, and cytosine and guanine can form three hydrogen bonds. Thus, adenine must pair with thymine, and cytosine must pair with guanine. Outside of complementary base pairing, the phosphate group and sugar create the side of the "ladder", structuring the DNA. The base pairs are bonded to the sugar, not the phosphate group.
  2. Replication is DNA creating more DNA with the enzyme DNA polymerase. This process is how the chromosomes are duplicated. It occurs during interphase. DNA "unzips" and never "zips" back together, and are used as a template for the new doulbe strands for DNA. Transciption is DNA creating RNA with the enzyme RNA polymerase. It creates many different kinds of RNA, including messenger RNA (mRNA), with is translated to produces proteins; transfer RNA (tRNA) and ribosomal RNA (rRNA), which are considered "machinery" for translation, and micro RNA (miRNA), which is regulatory. A single-stranded RNA is produced, and only the coding DNA is transcribed. Translation is RNA creating or coding for proteins with tRNA and mRNA, and it takes place in the ribosome. The genetic code is based on codons, which are strings of 3 nucleotides, creating 64 possible combinations for the 20 amino acids. This code is universal for all bacteria, protists, fungi, plants, and animals. tRNA binds one end to mRNA via an anticodon (complementary base pair), and the other end to an amino acid. There is at least one tRNA for each amino acid. The amino acid will connect to the protein chain created by mRNA when the complementary base pairs connect.
  3. A promotor region singles the transcription enzyme to begin copying the gene, and the terminator enzyme signals the transcription enzyme to fall off. An intron is an "intervening" part of the DNA, and is removed before the mRNA is finalized. An exon is an "expressed" part of the final DNA, and is kept in the final mRNA. This occurs in the nucleus. The finalized mRNA is transported to the cytosol for translation.
  4. DNA has deoxyribose as the 5-carbon sugar; is double stranded; and uses adenine, cytosine, guanine, and thymine as nitrogenous bases. DNA has ribose as the 5-carbon sugar; is single stranded; and uses adenine, cytosine, guanine, and uracil as nitrogenous bases.

Notes

Structure of DNA

DNA Functions

Central Dogma of Molecular Genetics

Replication

Gene Expression

Transcription

Gene Structure

mRNA Splicing

Non-Protein Coding DNA

Translation