Question

33PT1

Describe the functional properties of TFIID and TFIIH.

33 PT2.

Describe how lipid soluble hormones, glucocorticoid for example, regulate gene transcription acting through nuclear hormone receptors.

Answer 1

TFIID:

The general transcription factor II D (TFIID) is one of several general transcription factors that make up the RNA polymerase II preinitiation complex. Before the start of transcription, the transcription factor II D (TFIID) complex, binds to the core promoter of the gene.

TFIID is the first protein to bind to DNA during the formation of the pre-initiation transcription complex of RNA polymerase II (RNA Pol II). Binding of TFIID to the TATA box in the promoter region of the gene initiates the recruitment of other factors required for RNA Pol II to begin transcription. Some of the other recruited transcription factors include TFIIA, TFIIB, and TFIIF. Each of these transcription factors is formed from the interaction of many protein subunits, indicating that transcription is a heavily regulated process.

TFIIH:

Transcription factor II Human (Transcription Factor II H; TFIIH) is an important protein complex, having roles in transcription of various protein-coding genes and DNA nucleotide excision repair (NER) pathways. TFIIH first came to light in 1989 when general transcription factor-δ or basic transcription factor 2 was characterized as an indispensable transcription factor in vitro. This factor was also isolated from yeast and finally named as TFIIH in 1992.

The TFIIH consists of two main pieces the core with is the core XPB has these subunits p62, p52, p44, p34 and p8 and CAK composed of CDK7, cyclin H and MAT1. The unit that joins the core to the CAK is called XPD.

General function of TFIIH:

1. Initiation transcription of protein- coding gene.
2. DNA nucleotide repairing.

Hormones are typically divided into three classes:

1. Peptide: Hormones that are modified amino acids or short (peptide) or long (protein) chains of amino acids. Additionally, they can contain carbohydrate moieties.
2. Lipid: Steroid hormones that contain lipids synthesized from cholesterol and eicosanoids that contain lipids synthesized from the fatty acid chains of phospholipids found in the plasma membrane.

• Monoamine: Hormones derived from aromatic amino acids such as
  phenylalanine, tyrosine, and tryptophan.

Lipid and phospholipid-derived hormones are produced from lipids such as linoleic acid and arachidonic acid. Steroid hormones, which form the majority of lipid hormones, are derived from carbohydrates; for example, testosterone is produced primarily in the testes and plays a key role in development of the male reproductive system.

Eicosanoids are also lipid hormones that are derived from fatty acids in the plasma membrane. Unlike other hormones, eicosanoids are not stored in the cell—they are synthesized as required. Both are lipophillic and can cross the plasma membrane.

Lipid hormones include steroid and eicosanoid hormones. They are lipid-soluble and can pass through the plasma membrane.