Biology Chapter 15 Genes and Proteins

Genes and Proteins

• How does a cell use the information in DNA?

• Gene expression produces functional RNA or a polypetptide

• Changes in DNA can change gene expression or protein function

Gene expression produces functional _____ or a ______

RNA, or a polypeptide

Replication

copies DNA into DNA

Transcription

Copies a DNA sequence into RNA, one complementary single strand of RNA

Translation

uses an mRNA sequence to build a polypeptide

Genes can produce protein or RNA

• Each gene contains information for a functional product

• Protein coding genes produce mRNA for trnaslation

• Other genes produce functional RNA, including rRNA and tRNA

Each gene contains ____ for ___\

Information for a functional product

Protein coding genes produce _________

mRNA for translation

Other genes produce ________ including _____

functional RNAs including rRNA and tRNA

Transcription Produces ___

RNA

mRNA (messenger RNA)

“Record” information from DNA in the cell nucleus and carry it to the ribosomes. Single stranded message that you get off of one stand of DNA.

rRNA (Ribosomal RNAs)

Forms the ribosome’s core (physical structure) and helps catalyze polypeptide bonds

tRNA (Transfer RNA)

Physically Delivers amino acids one by one to protein chains growing at ribosomes

Gene expression in a eukaryote

Transcription makes pre-mRNA in the nucleus

RNA processing produces mature mRNA

• Removes introns; retains exons

mRNA exits the nucleus

Ribsomes translate mRNA in the cytoplasm

Gene expression in a eukaryote: Transcription makes pre-mRNA in the _______

nucleus

Gene expression in a eukaryote: RNA processing produces mature ____. This _____ introns, _____ exons

mRNA. Removes introns; retains exons

Gene expression in a eukaryote: ____ exits the nucleus, ribosomes translate mRNA in the cytoplasm

mRNA

Transcription Uses a DNA template

• DNA needs to be opened and exposed

• RNA polymerase reads one DNA strand for a gene

• RNA is complementary to the template strand

• RNA uses U in place of T

• The DNA strands pair again after the enzyme passes

• no SSB proteins like replication

DNA Polymerase and polymerase Read vs add relationship —

DNA Polymerase reads 3’ - 5’ prime, adds nucleotides 5’-3 prime

RNAE Polymerase reads 3’ - 5’ prime, adds nucleotides 5’-3 prime

RNA polymerase builds RNA

• The enzyme reads its DNA template 3’ to 5’

• It adds RNA nucleotides to the 3’ end, making RNA 5’ to 3’

• RNA Polymerase can begin without a primer

3 Steps of Transcription

Initiation

Elongation

Termination

Transcription: imitation

• a promoter helps position the transcription machinery

• IN eukaryotes, transcription factors recruit RNA polymer

• The DNA opens near the start site

• This will begin “writing the message”

Transcription: elongation

RNA polymerase opens a short stretch of DNA

Complementary RNA nucleotides extend the growing RNA

RNA separates from the template as DNA re-anneals (re stick together) and re-wind (behind it)

Unlike replication we do want the DNA we do want to DNA to stick back togther, so no SSB

Transcription: Termination

• The new RNA is cut near the end of the gene

• A poly-A tail is added to help protect the RNA

• RNA polymerase finished and detaches from the DNA

Eukaryotic genes: exons and introns

• Pre-mRNA contains exons and introns

• Splicing removes introns and joins exons

• Exons remain in mature RNA, including untranslated regions