GENE EXPRESSION

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RNA Splicing

Removing Introns

Ribozyme: attaches to pre-mRNA sequences and remove introns

Spliceosome: a complex region of small RNAs and proteins

Replication

DNA to DNA

DNA

ORI sequences

short stretches of DNA that have a specific sequence of nucleotides.

Prokaryotic Chromosome

*replication is BIDIRECTIONAL*

Proteins that initiate DNA replication recognize this sequence and attach to the DNA, separating the two strands and opening up a replication “bubble”

circular and has a SINGLE origin.

Eukaryotic Chromosome

linear stretch of DNA and have hundreds or even thousands of origins of replication

ENZYMES/PROTEINS IN DNA REP

DNA ligase

joins Okazaki fragments of lagging strand

DNA pol III

Using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to the 3’ end of the primer OR a pre-existing DNA strand

DNA pol I

Removes RNA nucleotides of the primer from the 5’ end and replaces them with DNA nucleotides added to the 3’ end of adjacent fragment

Primase

synthesizes the RNA primer at the 5’ end of leading strand and at 5’ end of Okazaki fragment of lagging strand.

Topoisomerase

relieves the tight strain from the untwisting of the DNA strand

Single Stranded Binding Protein

bind to each UNPAIRED DNA strand and keep them from forming back into the double helix

Helicases

BREAK HYDROGEN BONDS. It untwists the double helix at the replication forks, separating the two parental strands and making them available as template strands.

Structure: double helix, phosphate-sugar backbone outside the DNA molecule, each strand is anti-parallel to one another.

Nitrogenous Bases:adenine (A) with thymine (T), and guanine(G) with cytosine (C).

GENE EXPRESSION

Main topic

Transcription

DNA to mRNA

mRNA

TERMINATION

•RNA polymerase II transcribes a sequence of DNA called the polyadenylation signal sequence. This sequence specifies a polyadenylation signal (AAUAAA) in the pre-mRNA which causes the RNA polymerase II to cut the pre-mRNA transcript free

Eukaryote Modifications

occurs in the nucleus

Second Modification

First Modification

50-250 adenine nucleotides are added to form a poly-A-tail.

after the polyadenylation signal is transcribed (after transcription ends)

•At the end of the DNA sequence, RNA polymerase reads through and transcribes the terminator sequence •Transcription is halted •RNA polymerase disassociates from the DNA sequence, releasing mRNA

INITIATION

Transcription factors, a collection of proteins, mediate the binding of RNA polymerase II and the initiation of transcription. *transcription factors MUST attach to the promoter first before RNA polymerase II can bind to it. *

RNA polymerase II binds to the promoter. In Eukaryotes, the promotor is typically a TATA box upstream from the transcription start point.

DNA strands unwind

mRNA is transcribed at the start point on the template strand

RNA polymerase II initiates pre-mRNA synthesis at the transcription start point on the template strand

ELONGATION

•RNA nucleotides bind with the exposed DNA template strand. •RNA polymerase moves downstream, unwinding the DNA for pairing with RNA nucleotides •RNA polymerase adds nucleotides to the 3’ end of the growing pre-mRNA molecule. (that means the template strand runs from 3’-5’) •DNA strands are also formed back into a double helix

• Pre-mRNA nucleotides bind with the exposed DNA template strand. • The RNA polymerase II moves downstream, unwinding the DNA for pairing with RNA nucleotides • RNA polymerase II adds nucleotides to the 3’ end of the growing pre-mRNA molecule. (that means the template strand runs from 3’-5’) • DNA strands are also formed back into a double helix

RNA polymerase I: yields pre-MRA and MRNA during transcription

Eukaryotes

occurs in the nucleus, and the final mRNA is transported to the ribosomes in the cytoplasm.

Prokaryotes

occur simultaneously in the cytoplasm, and the mRNA is simultaneously converted into amino acid sequences of a polypeptide by the ribosomes.

RNA

Translation

mRNA to Protein

Chemical components

Release Factors

Elongation Factors

Initiation Factors

Peptidyl transferase: Formation of peptide bonds between amino acids

Amino Acids: Brought to the ribosome by tRNA and is attached to the growing chain of polypeptides.

mRNA : contains codons which code for a specific amino acid

tRNA: transfer RNA: the amino acid is attached to the 3’ end of the tRNA tRNAs have an ANTICODON. This anticodon matches the codon of the mRNA nucleotide

Ribosomes -small subunit and large subunit: where the amino acids are assembled into a polypeptide

Amino Acyl tRNA synthetase this is the enzyme that helps ADD the amino acid to the 3’ end of the tRNA.

Proteins