Presentation Transcript
From Genes to Proteins :From Genes to Proteins BIOLOGY
Introduction :The DNA in an organism leads to specific traits by dictating the synthesis of proteins.
Proteins are the links between genotype and phenotype.
For example, Mendel’s dwarf pea plants lack a functioning gene that stimulate the normal elongation of stems. Introduction
RNA : An Overview :Genes provide the instructions for making proteins.
Between DNA and protein synthesis is RNA.
RNA is chemically similar to DNA, except:
1. it contains ribose as its sugar
2. it substitutes the uracil for thymine
3. RNA molecules usually are single stranded.
There are three major classes of RNA: messenger, ribosomal, and transfer. RNA : An Overview Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Functions of RNA :Functions of RNA Messenger RNA (mRNA) takes a message from DNA in the nucleus to the ribosomes.
Ribosomal RNA (rRNA) along with proteins, makes up the ribosomes.
Transfer RNA (tRNA) transfers amino acids to the ribosomes for protein synthesis.
Slide 5:To get from DNA, written in one chemical language, to protein, written in another, requires two major stages, transcription and translation. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Slide 6:During transcription, a DNA strand is used to make an RNA strand.
Transcription of a gene makes a messenger RNA (mRNA) molecule.
During translation, the information in the mRNA is used to determine the amino acid sequence of a protein. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Slide 7:During transcription, one DNA strand, the template strand, provides for the sequence of nucleotides in RNA
Uracil replaces thymine.
During translation, blocks of three nucleotides, codons, are decoded into a sequence of amino acids.
mRNA has codons
tRNA has matching
anticodons Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 17.3
Nucleotide Triplets Specify Amino Acids :The genetic instructions for a protein are written in DNA as a series of three-nucleotide words.
Triplet code: three consecutive bases specify an amino acid, creating 43 (64) possible code words. Nucleotide Triplets Specify Amino Acids
Slide 9:Each codon = 1 of the 20 amino acids to be added next position along the polypeptide.
By the mid-1960s the entire code was deciphered.
61 of 64 triplets code for amino acids.
AUG codes
for methionine and
STARTS translation.
Three codons signal STOP. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings