Unit 8 Gene Transcription

These flashcards cover key vocabulary related to gene transcription, including nucleotides, RNA types, and processes involved in DNA and RNA synthesis.

Nucleotide

• The basic building block of nucleic acids (DNA and RNA).
• Consists of three components:
  • A pentose sugar (deoxyribose in DNA, ribose in RNA).
  • A phosphate group.
  • A nitrogenous base (purine or pyrimidine).

Purines

• Nitrogenous bases characterized by a double-ring structure (a six-membered ring fused to a five-membered ring).
• Examples include Adenine (A) and Guanine (G).
• These pair with pyrimidines via hydrogen bonds in nucleic acids.

Pyrimidines

• Nitrogenous bases characterized by a single six-membered carbon-nitrogen ring structure.
• Examples include Cytosine (C), Thymine (T) in DNA, and Uracil (U) in RNA.
• These pair with purines via hydrogen bonds in nucleic acids.

Antiparallel

• Describes the opposite orientations of the two complementary strands in a DNA double helix.
• One strand runs in the 5' to 3' direction, while the other runs in the 3' to 5' direction.
• This arrangement is crucial for DNA replication and transcription.

Base pairing

• The specific arrangement where complementary nitrogenous bases form hydrogen bonds with each other.
• In DNA:
  • Adenine (A) always pairs with Thymine (T) via two hydrogen bonds.
  • Guanine (G) always pairs with Cytosine (C) via three hydrogen bonds.
• In RNA, Adenine (A) pairs with Uracil (U).
• This specificity is fundamental to the accurate replication and transcription of genetic information.

RNA polymerase

• A crucial enzyme responsible for synthesizing RNA during transcription.
• It unwinds the DNA double helix locally.
• It reads the DNA template strand and adds complementary RNA nucleotides, forming an RNA strand.
• Does not require a primer to initiate synthesis.

mRNA

• Messenger RNA (mRNA) carries the genetic information from DNA in the nucleus to the ribosomes in the cytoplasm.
• It serves as a template for protein synthesis (translation).
• Each three-nucleotide sequence on mRNA (codon) specifies a particular amino acid.

tRNA

• Transfer RNA (tRNA) molecules are responsible for carrying specific amino acids to the ribosome during protein synthesis.
• Each tRNA has an anticodon loop that recognizes and binds to a complementary mRNA codon.
• It acts as an adapter molecule, translating the genetic code into a sequence of amino acids.

rRNA

• Ribosomal RNA (rRNA) is a major structural and catalytic component of ribosomes.
• Ribosomes, composed of rRNA and proteins, are the cellular machinery responsible for protein synthesis.
• rRNA plays a crucial role in forming peptide bonds between amino acids (peptidyl transferase activity).

Transcription

• The first step of gene expression, where genetic information from a specific segment of DNA is copied into an RNA molecule.
• Key stages include:
  • Initiation: RNA polymerase binds to the promoter region of a gene.
  • Elongation: RNA polymerase synthesizes a complementary RNA strand using the DNA template.
  • Termination: RNA synthesis stops, and the RNA molecule is released.
• The resulting RNA molecule can be mRNA, tRNA, or rRNA.

Deoxyribonucleic Acid (DNA)

• Deoxyribonucleic Acid (DNA) is the primary molecule responsible for carrying the genetic instructions used in the growth, development, functioning, and reproduction of all known organisms and many viruses.
• It is a double helix structure composed of two antiparallel polynucleotide strands.
• The backbone of each strand is made of alternating sugar (deoxyribose) and phosphate groups.
• Nitrogenous bases (A, T, C, G) extend inward and pair specifically through hydrogen bonds.

Ribonucleic Acid (RNA)

• Ribonucleic Acid (RNA) is a versatile nucleic acid involved in various crucial biological roles, primarily in gene expression and regulation.
• Key distinguishing features from DNA include:
  • Contains ribose sugar instead of deoxyribose.
  • Uracil (U) replaces Thymine (T) as one of the nitrogenous bases.
  • Typically single-stranded, although it can fold into complex 3D structures.
• Major types include mRNA, tRNA, and rRNA.

Directionality

• Refers to the chemical orientation of a nucleic acid strand, defined by the numbering of carbon atoms in the ribose or deoxyribose sugar.
• The 5' end has a phosphate group attached to the 5' carbon of the sugar.
• The 3' end has a hydroxyl group attached to the 3' carbon of the sugar.
• Nucleic acid synthesis always proceeds in the 5' to 3' direction.

Gene expression

• The fundamental process by which information encoded in a gene is used to synthesize a functional gene product, typically a protein or a functional RNA molecule.
• It involves two main stages:
  • Transcription: DNA is copied into RNA.
  • Translation: RNA (mRNA) is used as a template to synthesize a polypeptide chain (protein).
• Gene expression is tightly regulated to control the amount and type of gene products produced by a cell.

Hydrogen bonding

• A type of weak intermolecular force formed between an electronegative atom (like oxygen or nitrogen) and a hydrogen atom covalently bonded to another electronegative atom.
• In DNA, hydrogen bonds are crucial for:
  • Stabilizing the double helix structure by linking complementary nitrogenous bases across the two strands.
  • Specificity of base pairing: A-T pairs form two hydrogen bonds, G-C pairs form three hydrogen bonds, contributing to the helix's stability and accurate information transfer.
• These bonds are individually weak but collectively strong, allowing for easy separation of strands during replication and transcription.