the central dogma of molecular biology dna → rna → proteins biology ii d. mitchell
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The Central Dogma of The Central Dogma of Molecular Biology Molecular Biology
DNA → RNA → ProteinsDNA → RNA → Proteins
Biology IID. Mitchell
The Central Dogma of Molecular The Central Dogma of Molecular BiologyBiology
ReverseTranscription
DNADNA
DNA-Deoxyribonucleic Acid
The discovery of DNA’s structure clarified how DNA could serve as the
genetic material.
Contributions of ScientistsContributions of ScientistsHershey and Chase
◦Confirmed that DNA carries the genetic information
Erwin Chargaff◦The same four bases found in the DNA of all
organisms◦the amount of adenine = the amount of
thymine; the amount of guanine = the amount of cytosine.
Wilkins and Franklin◦Developed X-ray diffraction
photographs of DNA ◦X-rays revealed that DNA resembled
a tightly coiled helix composed of two or three chains of nucleotides.
Watson & Crick◦Used the information from Chargaff,
Franklin, and Wilkins◦Built a model of DNA with the
configuration of a double helix, a “spiral staircase” of strands of nucleotides twisted around a central axis.
Structure of DNAStructure of DNAIs a molecule that is a double helix -two
strands twisted around each other.
Each strand is composed of nucleotides.◦ Nucleotides are made of three parts: a phosphate
group, a sugar, and a nitrogen base.
five-carbon sugar : deoxyribosenitrogen bases : adenine, thymine,
guanine, and cytosine
Connecting the DNA moleculeConnecting the DNA molecule
Rails of the DNA ladder are alternating sugar & phosphates
Rungs are composed of pairs of bases
Strands of nucleotides are held together by hydrogen bonds between bases.
Base Pairing RulesBase Pairing Rules
Rule:Rule: a purine on one strand of DNA always pairs with a pyrimidine on the
opposite strand.
Adenine and Guanine are purines. Thymine and Cytosine are pyrimidines.
Adenine always pairs with ThymineGuanine always pairs with Cytosine
Purines are 2 ringed: Adenine or Guanine
Pyrimidines are 1 ringed: Thymine or Cytosine
The strictness of the base pairing results in two complementary strands.
The sequence of bases on one strand determines the sequence of bases on the other strand.
Example: TCGAACT AGCTTGA
DNA Complementary Strand DNA Complementary Strand PracticePractice
Replication of DNA Replication of DNA Replication - the making of an exact
copy of the DNA molecule Replication occurs whenever a cell
divides The copy must be 100% accurate
(errors = death possibly)
Stages in replication Stages in replication (basic)(basic)
1. DNA molecule is split in two at the end by the work of the enzyme DNA polymerase.
1. DNA unzips slightly
1. New nucleotides attach to the free ends
1. Process continues until completed
Results of ReplicationResults of Replicationresults in two (2) double strands of DNAeach strand is 50% new and 50% old DNA
Replication PracticeReplication Practice
RNARNARibonucleic AcidRibonucleic Acid
RNARNAFunction: protein synthesisLocation: found in ribosomes and the nucleolusStructure: Single helix composed of nucleotidesNitrogenous Bases: Adenine, Uracil, Guanine, and Cytosine
5-Carbon Sugar: Ribose
Three types of RNA:Three types of RNA:rRNA = ribosomal RNA - carries
protein building instructions. Goes from the DNA in the nucleus to the ribosome
◦mRNA = messenger RNA - is the message from DNA for the construction of the new protein molecule
◦tRNA = transfer RNA - delivers amino acids to the ribosomes. Has an anticodon specific to the amino acid.
DNADNA→RNA→Protein→RNA→ProteinDNA is TRANSCRIBED to
messenger RNA (mRNA)
mRNA carries the message to transfer RNA (tRNA)
tRNA is TRANSLATED to an amino acid chain, which makes up proteins
TranscTranscrription iption The copying of one side of the DNA
molecule that results in a single strand of RNA
During transcription, a DNA strand provides a template for the synthesis of a complementary RNA strand.
Transcription of a gene produces a messenger RNA (mRNA) molecule.◦ mRNA carries the message from the nucleus to the
ribosomes
Transcription PracticeTranscription Practice
TranslationTranslationThe reading of the RNA code to make
proteins or polypeptides. (protein synthesis)
The nucleotide sequence of mRNA determines the amino acid sequence that codes for a SPECIFIC protein.◦Translation occurs at ribosomes.
mRNA Codon ChartsmRNA Codon ChartsmRNA codon Charts are used for translation.
The genetic code consists of 64 triplets or codons of nucleotides. ◦groups of three bases on a mRNA strand
With three exceptions, each codon encodes for one of the 20 amino acids used in protein synthesis.
Processes In Eukaryotes And Processes In Eukaryotes And ProkaryotesProkaryotes
The basic mechanics of transcription and translation are SIMILAR.
Because bacteria lack nuclei, transcription and translation are coupled.
In a eukaryotic cell, almost all transcription occurs in the nucleus and translation occurs mainly at ribosomes in the cytoplasm.