PTT 207 Biomolecular and Genetic Engineering Semester 2 2013/2014 - - PowerPoint PPT Presentation

PTT 207 Biomolecular and Genetic Engineering

Semester 2 2013/2014

BY: PUAN NURUL AIN HARMIZA ABDULLAH

Content

I. INTRODUCTION II. RNA IS INVOLVED IN A WIDE RANGE OF CELLULAR PROCESSES

• III. STRUCTURAL MOTIFS OF RNA

3.1 INTRODUCTION

INTRODUCTION

• Chp 1 - Properties of DNA

Chp 3 - Properties of RNA

• RNA is now known to be involved in a wide range
• f essential cellular processes from DNA

replication to protein synthesis.

• The bottom line is that RNA has a much greater

structural versatility compared with DNA.

3.2 RNA IS INVOLVED IN A WIDE RANGE OF CELLULAR PROCESSES

RNA is involved in a wide range of cellular processes

• RNA is genetic information responsible for

the synthesis of proteins.

• The 6 major types of RNA are as follows:
• 1. Ribosomal RNA (rRNA)
• 2. Messenger RNA (mRNA)
• 3. Transfer RNA (tRNA)
• 4. Small nuclear RNA (snRNA)
• 5. Small nucleolar RNA (snocRNA)
• 6. MicroRNA (miRNA)

• 1. Ribosomal RNA (rRNA)
• rRNA is responsible for attaching new amino acids to the growing chain that will

eventually make up a protein.

• 2. Messenger RNA (mRNA)
• A single strand copy of a coding strand of DNA copied during a process

called transcription.

• 3. Transfer RNA (tRNA)
• tRNA carries amino acids to ribosomes in order to make sure the correct

amino acids are inserted into newly created proteins during protein synthesis.

• 4. Small nuclear RNA (snRNA)
• Plays a role in pre-mRNA splicing, a process which prepares the mRNA for

translation.

• 5. Small nucleolar RNA (snocRNA)
• Plays a role in rRNA processing.
• 6. MicroRNA (miRNA)
• Involved in post-transcriptional gene regulation; each miRNA binds to a

complementary sequence in a target mRNA, usually resulting in gene silencing, by triggering degradation of mRNA or by blocking translation by the ribosome.

Relationships among the 6 major types of RNA during gene expression.

• RNA can form complementary base pairs with
• ther nucleic acids.
• RNA can interact with proteins:

Ribonucleoprotein (RNP) particles

Two key points for understanding RNA function

3.3 STRUCTURAL MOTIFS OF RNA

Structural motifs of RNA

• RNA is a chain-like molecule composed of subunits

called nucleotides joined by phosphodiester bonds.

• Each nucleotide subunit is composed of 3 parts:
• A ribose sugar
• A phosphate group
• A nitrogenous base (adenine, guanine, cytosine,

uracil)

• Single-stranded RNA molecules fold into a variety of

secondary structural motifs that are stabilized by both Watson-Crick and unconventional base pairing.

• In Lecture 2, the DNA double helix forms from 2

separate DNA chains.

• In RNA, helix formation occurs within one ssRNA

chain of nucleotides.

• As for DNA, the RNA helix is stabilized by H-bonds

between base pairs and base-stacking hydrophobic interactions.

Secondary structure of RNA

• RNA adopts a right-handed A-type double helix

with 11 bp per turn.

• The 2’-hydroxyl group of the ribose in RNA

hinders formation of a B-type helix (the predominant form in dsDNA) but can be accommodate within an A-type helix.

• RNA is often recognized by RNA-binding proteins

in the minor groove.

Base-paired RNA adopts an A-type double helix

• RNA double helices often contain noncanonical or

non-Watson Crick base pairs.

• There are >20 different types of noncanonical bp

that have been found in RNA structures which includes the :

• 1. GU wobble
• 2. GA sheared
• 3. AU reverse Hoogsteen
• 4. GA imino

RNA helices often contain noncanonical base pairs

Base triples

• Typically involve one standard base pair

(most commonly either a Watson-Crick or a reverse Hoogsteen pair).

• The third base interacts in a variety of

unconventional ways.

RNA structures often contain unconventional base pairing

Important mediators of:

• RNA self-assembly.
• RNA-protein interactions.
• RNA-ligand interactions.

Noncanonical base pairs and base triples

So, does these base interactions have any functional significance?

• Yes, noncanonical base pairs and base triples

are important mediators of RNA self- assembly and of RNA-protein and RNA-ligand interactions.

• For example, noncanonical bp widen the

major groove and make it more accessible to ligands.

Bases in loops and bulges that are supposedly unpaired are often involved in a variety of long- range interactions, forming noncanonical bp.

Tertiary structure of RNA

• Examples of some common motifs are:
• Pseudoknot motif
• A-minor motif
• Tetraloop motif
• Ribose zipper motif
• Kink-turn motif
• Kissing hairpin loop

Tertiary structure of RNA

• The 3D structure is maintained by interactions between distant

nucleotides and interactions between 2’-OH groups.

• These long range interactions are less stable than Watson-Crick

bp and can be broken under mild denaturing conditions.

• Recall that RNA is negatively charged; thus tertiary structure

formation is a process that requires charge neutralization either through binding of a basic proteins or through binding of monovalent and/or divalent metal ions.

The End

Thank You