Notes on Nucleic Acids 2 types of nucleic acids: DNA – deoxyribonucleic acid RNA – ribonucleic...
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Transcript of Notes on Nucleic Acids 2 types of nucleic acids: DNA – deoxyribonucleic acid RNA – ribonucleic...
Notes on Nucleic Acids
2 types of nucleic acids:
DNA – deoxyribonucleic acid
RNA – ribonucleic acid
Chapter 8
• organic compounds
• large, made of subunits called nucleotides
Click image for interactive journey into human DNA
Each DNA nucleotide is made up of 3 parts:
1. Phosphate group
2. Deoxyribose – 5 carbon sugar
3. Nitrogen base – either adenine, thymine, cytosine, or guanine
Nitrogen bases
Purines – adenine (A) and guanine (G)
Pyrimidines – thymine (T) and cytosine (C)
The bases are held together by weak hydrogen bonds
Base pairings in DNA: A – T
C – G
A model of DNA was constructed in 1953 at Cambridge University in England
Scientist – James Watson, (1951-1953)
Field of study – biology
Country - America
Scientist – Francis Crick (1951-1953)
Field of study – biophysics
Country - England
Their model is described as a double twisted helix
(looks like a twisted ladder)
Watson and Crick published their proposed DNA double helical structure in a paper in the journal Nature in April 1953. In this paper Watson and Crick acknowledged that they had been "stimulated by.... the unpublished results and ideas" of Wilkins and Franklin.
Scientist – Maurice Wilkins, (1950-1953)
Field of study – biophysics
Country - England
Scientist – Rosalind Franklin, (1951-1953)
Field of study – Molecular Biology
(x-ray diffraction)
Country - England
Click image for interpret-ation of the X-ray
The process by which DNA builds an exact copy of itself - replication
• first the double helix must be unwound – this is done by enzymes called helicases
• then DNA polymerases (enzymes which move along each DNA strand) add nucleotides to the exposed bases
Replication occurs every time a cell divides, therefore passing the DNA code on into every cell
Genes are the DNA-encoded information that specifies particular proteins;
Each gene is made of a specific sequence of nucleotides
The working structures of genes are made of RNA
RNA structure:
1. Consists of a single strand of nucleotides
2. Ribose – a 5 carbon sugar
3. Uracil (U) instead of thymine (T)
uracil is paired with adenine
RNA base pairings: A – U
C – G
Three types of RNA
1. mRNA – messenger RNA
2. tRNA – transfer RNA
3. rRNA – ribosomal RNA
• All are needed for processing the information from DNA into proteins (gene expression)
Differences in DNA and RNA:
DNA RNA
1. double stranded single stranded
2. thymine uracil
3. nucleus only cytoplasm
4. deoxyribose sugar ribose sugar
Gene expression occurs in two stages:
1. Transcription – information in DNA is transferred to mRNA
2. Translation – the information in mRNA is used to make a protein
Roles of DNA & RNA in transmitting genetic information
• Story time: the analogy…
• Comp Book– Draw the Flow Map: DNA expression in the cell
• You need your pencil plus three colors:– Pencil will draw cell membrane/ cell parts/ labels– RED: DNA molecules– BLUE: any RNA molecules– PURPLE: protein
DNA RNA
RNA protein
1. Transcription (DNA RNA)
• occurs in nucleus
• begins with the enzyme RNA polymerase which binds to the promoter
Promoter – a specific sequence of DNA that acts as a “start” signal for transcription
Terminator – a sequence of bases that tells the RNA polymerase to stop adding nucleotides
Transcription Video
mRNA – is an RNA copy of a gene used as a blueprint for a protein
• carries hereditary information from DNA and delivers it to the site of translation
• acts as a template for the assembly of amino acids
tRNA – acts as an interpreter molecule
• translating mRNA sequences into amino acid sequences
rRNA – plays a structural role in ribosomes
2. Translation (RNA proteins)
• occurs in cytoplasm @ a ribosome
—both free ribosomes & ribosomes attached to ER
• uses nucleic acids to synthesize proteins
• involves all three RNA types:
—rRNA in the ribosome
—mRNA containing the genetic message
—message is made of codons
AUG-AAA-UAC-CCU-CCA-GCG-GGA
Codon – a series of three-nucleotide sequences
• each codon corresponds to an amino acid or signifies a start or stop signal
Write this down!
—tRNA carrying specific amino acids to be joined
a.a.
AUG-AAA-UAC-CCU-CCA-GCG-GGAmRNA
tRNA
UAC
tRNA
tRNA
tRNA
GGAAUG
GGU
ProtRNA
UUU
ribosome
Met
Lys TyrSer
Translation (Example)
Growing polypeptide
Translation: mRNA, tRNA & rRNA in cooperative action
…to make proteins!!!
AUG-AAA-UAC-CCU-CCA-GCG-GGAmRNA
tRNA
UAC
tRNA
tRNA
tRNA
GGAAUG
GGU
ProtRNA
UUU
ribosome
Met
Lys TyrSer
Translation (Repeated)
Growing polypeptide
Translation Video
A “Polysome”
Can you ID the 3 RNAs?
Awesome summary video from www.youtube.com
Click here to view