introduction to cells & microscopy nucleotide and nucleic
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Introduction to Cells & MicroscopyNucleotide and Nucleic Acid Structure
Adapted from Prof. Dean Tolan
• Outline of today’s supplemental lecture
• Nucleotide and nucleic acid structure
• Central Dogma
• Replication• Transcription• Translation
• Quiz at the end of the lecture
Structural Components of Nucleotides
Glycosidic bond
Table 3-1
Nucleic acid – polymer of nucleotides – directionality 5’3’
When you write a sequence:
ATCG
It is assumed that the 5’-end is on the left and the 3’-end is on the right, unless otherwise labeled.
5’-ATCG-3’
Phosphodiester bond
Chargaff’s Rules
B-Form DNA
http://higheredbcs.wiley.com/legacy/college/voet/0470129301/kinemages/exercise_2.html
Figure 3-8
Computer-simulated space-filling model of DNA.
Video: Computer-simulated space-filling model of DNA.
SUMMARY
(34 Å)
Right-handed, antiparallel, double-stranded helix. With the “basecomplementarity,” it explains genetic material:• Storage of genetic information• Replication• Information retrival
sugar–phosphate backbone (phosphodiester bonds)
Introduction to Cells & MicroscopyCentral Dogma of Molecular Biology
From DNA to Protein: Gene Expression
• Central Dogma: from Genes to Proteins• Replication of the genes (DNADNA)• Transcribing the information (DNARNA)• Translating the nucleotide sequence into
protein sequence (RNAProtein)– The Genetic Code– Protein Biosynthesis
Central Dogma
The central dogma of molecular biologyReplication
Information Flow
Replication
DNA replication is semiconservative (Meselson-Stahl Expt)
Arthur Kornberg showed that DNA contains information for its own replication.
He combined in a test tube: DNA, the four deoxyribonucleoside triphosphates (dNTPs–monomers), DNA polymerase, salts (Mg+2), and buffer.
The DNA served as a template for synthesis of new DNA.
DNA Replication
Each New DNA Strand Grows from Its 5´ End to Its 3´ End
ALL polymerases add nucleotides to the 3’ end
(Direction is termed 5’ 3’)
Pyrophosphatase
34
Each New DNA Strand Grows from Its 5´ End to Its 3´ End
Transcription
The central dogma of molecular biologyReplication
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
• What is the relationship between a DNA sequence and an amino acid sequence?
Central Dogma
RNA is key to this process:• Messenger RNA (mRNA)—carries
copy of a DNA sequence to site of protein synthesis at the ribosome
• Transfer RNA (tRNA)—carries amino acids for polypeptide assembly
• Ribosomal RNA (rRNA)—catalyzes peptide bond formation and provides structure for the ribosome
Central Dogma
Transcription
Transcription components:• A DNA template for base pairings—one of the two
strands of DNA• Nucleoside triphosphates (ATP,GTP,CTP,UTP) as
substrates• An RNA polymerase enzyme
Transcription process:• RNA polymerase unwinds DNA about ten base pairs at a
time; reads template in 3’ to 5’ direction, synthesizes RNA in the 5’ to 3’ direction.
• The RNA transcript is antiparallel to the DNA template strand, and adds nucleotides to its 3’ end.
• NTPs incorporate NMP and PPi is a product!
• Production of mRNA transcript by RNA polymerase
Transcription
Coding Region5' Flanking 3'-flanking
Transcription: Where to start?
Promoter
prokaryotes
The consensus sequence for each element in human genes (N is any nucleotide)
eukaryotes
Transcription
Translation
The central dogma of molecular biologyReplication
• What is the relationship between a DNA sequence and an amino acid sequence?
Central Dogma
Messenger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
• The Code• The Adaptors (tRNA)• The Ribosome (rRNA + rProteins)
Translation: The Genetic Code
The genetic code: Specifies which amino acids will be used to build a protein
Codon: A sequence of three bases—each codon specifies a particular amino acid.
Start codon: AUG—initiation signal for translation.
Stop codons: UAA, UAG, UGA—stop translation and polypeptide is released.
Translation: The Genetic Code
The genetic code is redundant. The genetic code is universal.
Translation: tRNA
tRNAs must deliver amino acids corresponding to each codon
The conformation (three-dimensional shape) of tRNA results from base pairing (hydrogen bonding) within the molecule.
3‘-end is the amino-acid attachment site—binds covalently.
At the other end (middle of the tRNA sequence) is the Anticodon—site of base pairing with mRNA. Unique for each species of tRNA.
Translation: tRNA
tRNAanticodon
Template for mRNA –read 3’5’
Translation: tRNA
N C
Translation: Ribosome
Ribosome: the workbench—holds mRNA and charged tRNAs in the correct positions to allow assembly of polypeptide chain.
Ribosomes are not specific, they can make any type of protein.
Translation: Protein Biosynthesis: Ribosome Structure
Ribosomes have two subunits, large and small. When not active in translation, the subunits exist separately.• The small subunit (40S) has one ribosomal RNA (rRNA) (18S) and 33
proteins.• The large subunit (60S) has three molecules of rRNA (28S, 5.8S, 5S)
and 49 different proteins.• Ribosomal subunits are held together by ionic and hydrophobic forces
(not covalent bonds) (80S).
Translation: Ribosome
Translation: Protein Biosynthesis; Elongation
Decoding(GTP hydrolysis)
Peptidyltransferase
GTPEF-Tu
Translation: Protein Biosynthesis; Elongation
Translocation(GTP hydrolysis)
ELONGATION
Central Dogma
The central dogma of molecular biologyReplication
Animated videos of DNA structure and Central Dogma
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