Post on 26-Dec-2015
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
http://www.dnai.org/a/index.html
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
http://www.dnai.org/a/index.html
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