Genetics - Exam 2 - Transcription

Gene

DNA sequence that codes for a functional product (RNA or protein).

Regulatory sequence

DNA regions and biochemical signals that control gene expression.

Transcription

Synthesis of RNA from a DNA template.

Promoter

DNA sequence where RNA polymerase binds to start transcription.

RNA polymerase

Enzyme that builds RNA.

Template strand

DNA strand used by RNA polymerase to make RNA.

Nontemplate strand (coding strand)

DNA strand not used; has same sequence as RNA (except T = U).

Transcription bubble

Region where DNA is unwound for RNA synthesis.

Termination sequence

DNA signal that ends transcription.

List and describe the three ways that RNA differs from DNA

• Sugar - RNA has ribose, DNA has deoxyribose.

• Bases - RNA uses uracil (U) instead of thymine (T).

• Structure - RNA is usually single-stranded; DNA is double-stranded.

mRNA (messenger RNA)

Carries the genetic “recipe” from DNA to ribosomes.

tRNA (transfer RNA)

Brings amino acids to ribosomes during translation (functional RNA). rRNA (ribosomal RNA)

Describe where transcription occurs in the cell

• Eukayotes - In nucleus

• Prokaryotes - Occurs in cytoplasms (since they lack a nucleus)

Initiation

• RNA polymerase binds to promoter.

• DNA unwinds → transcription bubble forms.

• Template strand is chosen.

Elongation

• RNA polymerase adds RNA nucleotides complementary to template strand.

• RNA grows 5′ → 3′ only.

• RNA sequence corresponds to gene being transcribed.

Termination

• RNA polymerase reaches termination sequence.

• Protein factors help release RNA transcript.

• RNA polymerase detaches from DNA.

rRNA

Forms part of ribosome structure and catalyzes protein synthesis (functional RNA).