Molecular GeneticsDNARNA

Gene Expression

DNA deoxyribonucleic acid◦ Deoxribose sugar◦ 2 strands held together with H bonds◦ ATGC are the nitrogen bases◦ Double helix◦ Found only inside the nucleus

RNA ribonucleic acid◦ Ribose sugar and AUGC nitrogen bases◦ 1 strand◦ 4 types, mRNA, tRNA, rRNA, and snRNA

DNA and RNA

Compare RNA and DNA

DNA replication◦ Replication is semi-conservative◦ Occurs during interphase when each chromosome

makes an exact copy (sister chromatid)

Replication

◦Involves several enzymesHelicase- unwinds the helix DNA polymerase- adds new nucleotide units to the parent strand of DNA

Ligase- connects the new strand and zips the molecule together. http://www.dnai.org/a/index.html

DNA Replication cont’d

At the end of each DNA molecule is a section of noncoding nucleotides called a telomere

Problem with replication?

Each time a cell divides and replicates its DNA a small part of the telomere is lost

This loss of telomere limits the number of times a cell can divide.

This erosion of the telomere during cell division is linked to the aging process and cancer

The enzyme telomerase is inactive in somatic cells but is active in cancer tumors.

Can you identify the function of telomerase????

Telomere cont’d

Chromatin In each cell DNA

molecules are organized and wrapped around small proteins called histones.

The density of this wrapping is directly related to the expression of the genes found on the chromosome.

Dense wrapped – no gene expression

Lose wrapped – open to gene expression

Genes are located on the chromosome at a particular loci

When the gene is signaled to be expressed a series of enzymes go to work

helicase, RNA polymerase, ligase Transcription occurs when the template

strand of DNA is exposed and mRNA is made

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Gene experssion

Process of making a mRNA molecule from the DNA template.

DNA - A T A G C A T A C T A G G mRNA- U A U C G U A U G A U C C

Transcription occurs with in the nucleus, after the mRNA is made however it goes through a series of modifications call RNA processing.This process allows for one gene to express multiple proteins, and is considered to be an element of the evolution process.

Transcription

mRNA leaves the nucleus of the cell and moves into the rough ER.

A ribosome attaches to the mRNA and starts to Translate the sequence of nucleotides into a protein.

Translation involves several players: rRNA, mRNA, tRNA, amino acids, and enzymes

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Protein Synthesis

Translation occurs at the ribosome, and reads the mRNA 3 nucleotides at a time

3 nucleotides make up a codon, which codes for 1 amino acid.

There are 64 different codons and only 20 amino acids. So there is repetition in the code

AUG is the universal start codon and codes for the amino acid Met.

There are 3 stop codons that terminate translation: UGA, UAA, UAG

Translation

Once the codon enters the ribosome the complementary, anticodon, of the tRNA attaches to the mRNA.

The tRNA carries with it a specific amino acid, the amino acids are then bonded to each other as each sequential codon is read by the ribosome

http://www.dnai.org/a/index.htmlThe end result is a very specific amino acid chain called a polypeptide or protein.

Translation cont’d