RNA and Protein RNA and Protein SynthesisSynthesis

The Function of DNAThe Function of DNA The DNA molecule The DNA molecule

contains all of your contains all of your hereditary information hereditary information in the form of genes.in the form of genes.

Genes are portions of Genes are portions of the DNA molecule that the DNA molecule that code for the production code for the production of specific types of of specific types of proteins. proteins.

However, DNA is However, DNA is confined to the confined to the nucleus, while proteins nucleus, while proteins are made by ribosomes are made by ribosomes in the cytoplasm.in the cytoplasm.

Thus, a messenger Thus, a messenger molecule is needed.molecule is needed.

http://www.accessexcellence.org/RC/VL/GG/images/genes.gif

Comparing DNA and Comparing DNA and RNARNA

RNA is the nucleic acid RNA is the nucleic acid that acts as a messenger that acts as a messenger between DNA and the between DNA and the ribosomes.ribosomes.

The RNA produced during The RNA produced during transcription is transcription is structurally different from structurally different from DNA in 3 basic ways:DNA in 3 basic ways: 1. The sugar in RNA is 1. The sugar in RNA is

ribose whereas the sugar in ribose whereas the sugar in DNA is deoxyribose.DNA is deoxyribose.

2. RNA is single stranded 2. RNA is single stranded while DNA is double while DNA is double stranded.stranded.

3. RNA contains a base 3. RNA contains a base called uracil instead of called uracil instead of thymine.thymine. http://www.dkimages.com/discover/previews/

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Protein SynthesisProtein Synthesis

During protein synthesis, genes copied During protein synthesis, genes copied onto RNA are expressed by the onto RNA are expressed by the production of specific types of proteins.production of specific types of proteins.

Protein synthesis involves two Protein synthesis involves two processes:processes: 1. Transcription – the process where a 1. Transcription – the process where a

portion of the DNA sequence is copied into portion of the DNA sequence is copied into a complementary RNA sequence.a complementary RNA sequence.

2. Translation – the decoding of an mRNA 2. Translation – the decoding of an mRNA message into a polypeptide chain (protein).message into a polypeptide chain (protein).

TranscriptionTranscription

Transcription occurs on the DNA in Transcription occurs on the DNA in the nucleus.the nucleus.

Transcription Demo

Types of RNATypes of RNA The RNA produced during transcription is modified The RNA produced during transcription is modified

into 3 basic types:into 3 basic types: 1. messenger RNA (mRNA) is responsible for copying one 1. messenger RNA (mRNA) is responsible for copying one

strand of DNA in the nucleus and carrying that information to strand of DNA in the nucleus and carrying that information to the ribosomes in the cytoplasm.the ribosomes in the cytoplasm.

2. ribosomal RNA (rRNA) makes up a large part of the 2. ribosomal RNA (rRNA) makes up a large part of the ribosome and is responsible for reading and decoding mRNA.ribosome and is responsible for reading and decoding mRNA.

3. transfer RNA (tRNA) carries amino acids to the ribosome 3. transfer RNA (tRNA) carries amino acids to the ribosome where they are joined to form proteins.where they are joined to form proteins.

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TranslationTranslation

Translation is completed by the Translation is completed by the ribosomes located in the cell’s ribosomes located in the cell’s cytoplasm.cytoplasm.

All three types of RNA work together All three types of RNA work together during translation to produce during translation to produce polypeptides (proteins).polypeptides (proteins).

Translation Demo

Decoding mRNADecoding mRNA The sequence of bases in an mRNA molecule The sequence of bases in an mRNA molecule

serves as instructions for the order in which serves as instructions for the order in which amino acids are joined to produce a amino acids are joined to produce a polypeptide.polypeptide.

Ribosomes decode these instructions by Ribosomes decode these instructions by using codons, sets of 3 bases that each code using codons, sets of 3 bases that each code for 1 amino acid.for 1 amino acid.

Each codon is matched to an anticodon, or Each codon is matched to an anticodon, or coplementary sequence on the tRNA to coplementary sequence on the tRNA to determine the order of the amino acids.determine the order of the amino acids.

http://www.gwu.edu/~darwin/BiSc150/One/codon.gif

Using a Codon ChartUsing a Codon Chart When given a sequence of mRNA When given a sequence of mRNA

bases, a codon chart can be used to bases, a codon chart can be used to determine the sequence of the determine the sequence of the amino acids in the polypeptide.amino acids in the polypeptide.

http://www.safarikscience.org/biologyhome/7_dna/codon_question.png

Decoding PracticeDecoding Practice For the following examples, give the For the following examples, give the

appropriate mRNA sequence and amino acid appropriate mRNA sequence and amino acid sequence. sequence. (Remember: U replaces T in mRNA.)(Remember: U replaces T in mRNA.)

Example 1:

DNA: TAC GCA TGG AAT

mRNA: AUG CGU ACC UUA

Amino Acids: Met Arg Thr LeuExample 2:

DNA: CGT GGA GAT ATT

mRNA: GCA CCU CUA UAA

tRNA: CGU GGA GAU AUU

Amino Acids: Ala Pro Leu stop