Group

Roll no. 13 to 23Section: A DPTPhysiology Presentation

> In respect of Dr. Muzna Munir

Maryam Nadeem

TOPIC OUTLINETranscriptionTypes of RNA

Messenger RNA(mRNA) or Codons

Transfer RNA (tRNA) or Anticodons

Ribosomal RNA (rRNA)MicroRNA (miRNA)

or Noncoding RNA

What is DNA?Deoxyribonucleic acid, a self replicating

material which is present in nearly all living organisms as the main component of

chromosomes. It is the carrier of genetic information.

TranscriptionTranscription is the first step of gene expression, in which a particular segment of DNA is copied into RNA by an enzyme RNA polymerase.

RNA Polymeraseo Also known as DNA-dependent RNA

polymeraseo In process of Transcriptiono  essential to life and are found in all

organisms and many viruses.

DNA Code transfer into cytoplasm-Transcription…

Location of DNA

DNA used to Make Proteins

DNA CODE IN THE CELL NUCLEUSIntroduction

Syeda Faiqa Rehman

What is DNA?DNA is (deoxyribose nucleic acid) a molecule

that encodes the genetic instructions used in the development and functioning of all living organism.

DNA is a self replicating material which is present in nearly all living organisms as a main constituent of chromosomes.

In one chromosomes 25000 genes are present.The thickness of DNA is almost 2nm.10 base pairs are present in one turn.The length of one turn of DNA is 3.4 nm.

DNA Composed of:1.nitrogenous bases2.phosphate group3.deoxyribose sugar

Location of DNA:DNA is located in the nucleus of the cell .yet most of the functions of the cell are carried out in the cytoplasm, there must be some means for the DNA genes of the nucleus to control the reactions of the cytoplasm. This is achieved through the intermediary of another type of nucleic acid, RNA, the formation of which controlled by DNA of the nucleus. thus figure shown the coding of DNA coded information into RNA coded information this process called transcription. the RNA in turn diffuses from the nucleus through pores into cytoplasmic compartment, where it control protein synthesis.

TRANSCRIPTION:In transcription process the firstly combination of ribose nucleotides with strand of DNA to form a molecule of RNA that carries the genetic code from the gene to the cytoplasm. The RNA polymerase enzyme moves along the DNA strand & builds the RNA molecule.

Synthesis of RNA:Temporarily uncoiling of DNA.

During synthesis of RNA the two strands of DNA molecule separate temporarily; one of these strands use for synthesis of RNA molecule.TRIPLET CODES:The genetic code in which a sequence of three nucleotides on DNA molecule codes for template strand whose complementary RNA strand is formed.

Basic building block of RNA:

RNA composed of :Ribose sugar Thymine is replaced by uracilRNA is single stranded structure.

Formation of RNA nucleotides:

RNA contain four types of nucleotides:Adenine GuanineCytosineUracil

Difference between DNA and RNA DNA RNADNA is a deoxyribonucleic acid. RNA is ribonucleic acid.

DNA is a double helix molecule. RNA is single helix molecule.

DNA contain two polynucleotide chain.

RNA contain one poly nucleotide chain.

DNA is present only in nucleus. RNA is present in whole of the cell in the cytoplasm as well as in nucleus.

DNA contain A,C,G,T. nitrogenous bases.

RNA contain A,T,C,U nitrogenous bases.

DNA act as hereditary material in all organism.

RNA act as a hereditary material in some viruses.

DNA has no types. RNA has three types MRNA, RRNA, TRNA.

Hafiza Natasha Hira

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In The Synthesis of RNA the activation is done by an enzyme which is called “RNA Polymerase”.

Activation of the RNA Nucleotides.

TRANSCRIPTION:The process in which genes of DNA i.e., DNA code is expressed in the form of mRNA is called Transcription. DNA is responsible for this process.

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It is an enzyme that catalyses the formation of RNA from DNA strand during transcription. It is also called “Transcriptase”

RNA POLYMERASE

This process is done by adding to each nucleotide to extra phosphate radicals to form triphosphates these last two phosphates are combined with the nucleotide by “High energy phosphates” derived from ATP in the cell. RESULT The result of this activation process is that large quantities of ATP energy are made available to each of the nucleotides and this is used to promote the chemical reactions That add each new RNA nucleotide at the end of the developing RNA chain.

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STEP 01: In the DNA strand immediately ahead of the initial gene is a sequence of nucleotides called promoter. The RNA polymerase has an appropriate complementary structure that recognizes this promoter and becomes attached to it.

STEPS Involved in TRANSCRIPTION

Click icon to add pictureAfter the RNA polymerase attaches to the promoter the polymerase causes unwinding of about two turns of the DNA helix and separation of the unwounded portions of the two strands

STEP 02:

Kanwal Yaqoob

Then the polymerase moves along the DNA strand and, temporarily

a) First it causes hydrogen bonds to form between the ends of an RNA nucleotides in the nucleoplasm.

STEP 03

Click icon to add pictureThen one at a time the RNA polymerase breaks 2 of the 3 phosphate radicals away from each of these RNA Nucleotides…………….

B)

Click icon to add pictureWhen the RNA polymerase reaches the end of the DNA gene it encounters a new sequence of DNA nucleotides called the chain terminating sequence…………………

c)

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As the new RNA strand is formed its week hydrogen breaks away thus the RNA chain is forced away from the DNA and released into nucleoplasm.

d)

The code that is present in DNA strands is transmitted in complementary form to the RNA.

In short,

Natasha Ramzan

The ribose nucleotide bases always combine with deoxyribose bases in the following combinations :

Combination of Bases:

DNA Base RNA Base

Guanine Cytosine

Cytosine Guanine

Adenine Uracil

Thymine Adenine

RNA:• Ribonucleic acid, or RNA is one of the three major

biological macromolecules that are essential for all known forms of life (along with DNA and proteins).

• DNA makes RNA, RNA makes Proteins.

Each type of RNA plays and independent and entirely different role in protein formation.There are four different types of RNA :

1- Messenger RNA2- Ribosomal RNA3- Transfer RNA4- Micro RNA

Types of RNA :

Which carries the genetic code to the cytoplasm for controlling the type of protein formed.

Messenger RNA:

Which transports activated amino acids to the ribosomes to be used in assembling the protein molecules.

Transfer RNA:

Which, along with about 75 different proteins, forms ribosomes, the physical and chemical structures on which protein molecules are actually assembled.

Ribosomal RNA:

Micro RNA:About 21 to 23 nucleotides that cannot be translated and they regulate gene expression.

Tasbeeha Munir

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MESSENGER RNA

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TOPIC OUTLINE m-RNA Structure Function Codon

Biochemistry For Medics 46

Messenger RNA (m-RNA)

• Comprises only 5% of the RNA in the cell• Most heterogeneous in size and base sequence• All members of the class function as

messengers carrying the information in a gene to the protein synthesizing machinery

mRNA STRUCTURE AND

FUNCTIONS

Structural Characteristics of m-RNA

The 5’ terminal end is capped by 7- methyl guanosine triphosphate cap.

The cap is involved in the recognition of mRNA by the translating machinery

It stabilizes m RNA by protecting it from 5’ exonuclease

Structural Characteristics of m-RNA(contd.)

The 3’end of most m-RNAs have a polymer of Adenylate residues( 20-250)

The tail prevents the attack by 3’ exonucleases Histones and interferons do not contain poly A

tails On both 5’ and 3’ end there are non coding

sequences which are not translated (NCS)

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Structural Characteristics of m-RNA

5’ cap and 3’ tail impart stability to m RNA by protecting from specific exo nucleases.

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RNA CODON The m- RNA molecules are formed with the

help of DNA template during the process of transcription.

The sequence of nucleotides in m RNA is complementary to the sequence of nucleotides on template DNA.

The sequence carried on m -RNA is read in the form of codons.

A codon is made up of 3 nucleotides The m-RNA is formed after processing of

heterogeneous nuclear RNA

Hafiza Mehmoona

What is rRNA:In molecular biology, ribosomal ribonucleic acid (rRNA) is the RNA component of the ribosome, and is essential for protein synthesis in all living organisms. It constitutes the predominant material within the ribosome, which is approximately 60% rRNA and 40% protein by weight. Ribosomes contain two major rRNA and 50 or more proteins.

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Structure:The ribosomal RNAs form two subunits, the large subunit (LSU) and small subunit (SSU). mRNA is sandwiched between the small and large subunits.A ribosome also has three binding sites called A, P, and E.The A site in the ribosome binds to an aminoacyl-tRNA (a tRNA

bound to an amino acid).The amino (NH2) group of the aminoacyl-tRNA, which contains the

new amino acid, attacks the ester linkage of peptidyl-tRNA (contained within the P site), which contains the last amino acid of the growing chain, forming a new peptide bond. This reaction is catalyzed by peptidyl transferees.

The tRNA that was holding on the last amino acid is moved to the E site, and what used to be the aminoacyl-tRNA is the peptidyl-tRNA.

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Formation of rRNA in nucleolus:

As the rRNA forms it collects in the nucleolus.In nucleolus it binds with ribosomal proteins to form

granular condensation products that are predominant subunits of ribosomes

Subunits release from nucleolus and transported through nuclear pores to almost all parts of cytoplasm.

In cytoplasm rRNA assembled to form mature, functional ribosomes.

Therefore, proteins are formed in the cytoplasm of cell not in nucleolus as it doesn’t contain mature ribosomes.

Size of nucleolus depends upon no. of rRNA present in it.

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Synthesis of rRNA:

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Location in cell:The DNA genes for formation of rRNA are located in five pairs of chromosomes in the nucleolus, each chromosome contain many duplicates of these particular genes because of large amount of rRNA required for cellular functions.

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Process of Translation:It is the whole process by which the base

sequence of an mRNA is used to order and to join the amino acids into a protein.

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Role of rRNA in translation:All types of RNA takes part in process of

translation.rRNA associate with a set of proteins to

form ribosomes.These complex structures, which

physically move along an mRNA molecule, catalyzed the assembly of amino acids into protein chains.

They also binds tRNAs and various accessory molecules necessary for protein synthesis. 61

In protein synthesis:

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Muzzama Mansoor

Transfer RNA

Small RNA moleculeClover leaf appearanceTransfers amino acids to protein moleculesContains 80 nucleotidesEach tRNA is specific for each amino acidEach tRNA recognizes specific codon on

mRNA45 different types of tRNA are present in

humans

Transfer RNA-The Anticodon:

Anticodon:The specific code in the tRNA that allows it to recognize a specific codon is a triplet of nucleotides bases and is called an anticodon.Anticodon bases combine loosely by hydrogen bonding with the codon bases of mRNA.

Works as carrier of amino acidsParticipates in protein synthesis (Translation)

Functions:

Also known as adenosine mono phosphate AMPCONSISTS of ribose, adenine, 1 phosphateOne end of tRNA is always adenylic acidA.A attaches at -OH group of ribose in adinylic acid of tRNA

Adenylic acid:

Manahil Hashmi

Micro RNA (miRNA)

Definition

A microRNA (abbreviated miRNA) is a small non-coding RNA molecule (containing about 22

nucleotides) found in plants, animals, and some viruses, which functions in RNA silencing and post-

transcriptional regulation of gene expression.

Discovery…For the first time in Caenorhabditis elegans-a

free living nematode by Victor Ambros’ Laboratory in 1993.

Peculiarities… Encoded from transcribed DNA but not translated into

protein and hence called non-coding RNA. Regulate many functions of cells playing key role in: > cell development, differentiation, death,

proliferation, apoptosis, neurodevelopment and indirectly in Translation. > siRNA(discussed later) may become useful therapeutic tools to silence genes that contribute to the pathophysiology of diseases.

Hamza Nafees

Formation…

Long primary precursor RNA pri-miRNA is processsed in the nucleus to form pre-miRNA by microprocessor complex.

Pre-miRNA is 70 neucleotide stem loop structure. Pre-miRNA is processed in cytoplasm by a Dicer enzyme that assembles miRNA and RNA Induced Silencing Complex (RISC)

Functions… It performs RNA Silencing by introducing anti-

sense RNA molecules in mRNA. It regulates gene expression by controlling

process of Translation. it reduces efficiency of mRNA in protein

synthesis. this is done by another type of miRNA-a silencing

RNA(siRNA) or short RNA 20-25 nucleotides. The siRNA are short double stranded RNA

molecules, 20-25 nucleotides in length. as siRNA enters cytoplasm, it activates RISC that

was generated along with miRNA.

References… Bernice J, Heffner DR, Stark A, Russell RB, Cohen SM (2003) bantam encodes a developmentally regulated microRNA that controls cell

proliferation and regulates the proapoptotic gene hid in Drosophila. Cell 113: 25-36. Colin GA, Sevignani C, Dumitru CD, Hyslop T, Noch E, Yendamuri S, Shimizu M, Rattan S, Bullrich F, Negrini M, Croce CM (2004) Human

miRNA genes are frequently located at fragile sites and genomic regions involved in cancers. Proc. Natl. Acad. Sci. USA. 101: 2999-3004. Dostie J, Mourelatos Z, Yang M, Sharma A, Dreyfuss G. (2003) Numerous microRNPs in neuronal cells containing novel microRNAs. RNA 9(2):

180-6. Erratum in: RNA 9(5): 631-2. Chen X. (2003) A MicroRNA as a Translational Repressor of APETALA2 in Arabidopsis Flower Development. Science E-Pub. Krichevsky AM, King KS, Donahue CP, Khrapko K, Kosik KS (2003) A miRNA array reveals extensive regulation of miRNAs during brain

development. RNA 9: 1274-1281. Lee RC, Feinbaum RL, Ambros V (1993) The C. elegans heterochronic gene lin-4 encodes small RNAs with antisense complementarity to lin-14.

Cell 75: 843-854.

Lim LP, Glasner ME, Yekta S, Burge CB, Bartel DP (2003b) Vertebrate microRNA genes. Science 299: 1540.

Metzler M, Wilda M, Busch K, Viehmann S, Borkhardt A. (2004) High expression of precursor miRNA-155/BIC RNA in children with Burkitt lymphoma. Genes Chromosomes Cancer 2: 167-169.

Michael MZ, O’Connor SM, van Holst Pellekaan NG, Young GP, James RJ (2003) Reduced accumulation of specific microRNAs in colorectal neoplasia. Molecular Cancer Research 1: 882-91.

Pfeffer S, Zavolan M, Grasser FA, Chien M, Russo JJ, Ju J, John B, Enright AJ, Marks D, Sander C, Tuschl T. (2004) Identification of virus-encoded microRNAs. Science 304(5671): 734-6.

Reinhart BJ, Slack FA, Basson M, Pasquinelli AE, Bettinger JC, Rougvie AC, Horvitz HR, and G Ruvkun. (2000) The 21 nucleotide let-7 RNA regulates C. elegans developmental timing. Nature 403: 901–906.

Xu P, Vernooy SY, Guo M, Hay BA. (2003) The Drosophila microRNA Mir-14 suppresses cell death and is required for normal fat metabolism. Curr Biol 13(9): 790-5.

Guyton and Hall Medical Physiology; ed 12 Genetic Control of Protein Synthesis, Cell Function, and Cell Reproduction_Unit-1_ The process of Transcription.