chapter 12 dna and rna. what is dna again? deoxyribonucleic acid long double-stranded molecule of...
TRANSCRIPT
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Chapter 12DNA and RNA
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What is DNA again?Deoxyribonucleic acidLong double-stranded molecule of
nucleotidesStores genetic code that is transferred
to future generations and cellsCodes for synthesis of proteins
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What is a nucleotideA nucleotide has 3 parts:
◦A sugar (deoxyribose for DNA)◦A phosphate group◦A nitrogen base
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Nitrogen base pairingThe order of nitrogen bases are what
determines your genetic codeThe order of the bases determines the
proteins that are made4 different bases exist:
◦Purines: Guanine, Adenine Grade A Pure
◦Pyrimidines: Cytosine, ThyminePairing is also called Chargaff’s Rule
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Chargaff’s Rule
Result: A=T, G=C
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But what is the structure?In the early 1950s Rosalind Franklin
used X-ray diffraction took a “picture” of DNA◦Difficult to tell what the structure is
from the image◦Strands twisted around one another
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But what is the structure?James Watson and Francis Crick used
Franklin’s images and their models to determine the correct structure: double helix◦Two strands wound around one
another◦“Twisted ladder”◦Later discovered that hydrogen
bonds hold the two sides of the ladder together
◦Can only from between adenine and thymine, or guanine and cytosine (A=T, G=C)
◦The base pairing explained Chargaff’s Rule
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DNA Structure
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DNA Structure DNA is very long; E. coli’s contains
4,639,221 base pairs (length =1.6 mm)◦Must fit in an organism 1/1000 its
length◦Must be packed very tightly to fit
Human cell contains almost 100 times the base pairs◦Chromatin consists of DNA packed
around proteins called histones◦These compact together during
mitosis to create our visible chromosomes
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DNA Structure
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DNA replicationRemember that before a cell divides it
has to copy its DNA◦If we separate each strand, we can
use it to make a copy of the other◦If we have an A, we match it with a
T; if a G, we match it with a C (called complementary)
In prokaryotes, replication begins at one point and proceeds typically in both directions
In contrast, eukaryotes begin replication in hundreds of locations (due to its longer length)
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DNA Replication
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DNA replicationTwo replication forks formed, each
strand has a new complementary strand added◦TACGTT ATGCAA◦Results in two identical DNA
molecules◦One strand is new, the other old
DNA was unzipped (breaking of hydrogen bonds)◦DNA polymerase (enzyme) joins
individual nucleotides to produce a DNA molecule
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What is RNA?Ribonucleic acidIntermediate molecule between DNA
and proteinsDiffers from DNA in 3 ways:
◦Single stranded (vs. double)◦Ribose instead of deoxyribose◦Utilizes uracil instead of thymine (A-
U, G-C)
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Type of RNAThere are 3 types of RNA:
◦messenger RNA (mRNA)- carries copies of the protein instructions
◦ribosomal RNA (rRNA)- makes up the ribosome, along with several proteins
◦transfer RNA (tRNA)- take the appropriate (base pairing anti-codon to codon) amino acid to the ribosome
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Types of RNA
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Protein synthesis: how we make proteins?Two processes or steps:
◦Transcription- mRNA is made from the DNA and travels to the cytoplasm to find a ribosome
◦Translation- tRNA brings to the ribosome the amino acids to build the primary structure of a protein and the result is a free polypeptide that will then fold up into the shape of the protein
Remember: amino acids are held together by peptide bonds
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Transcription
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TranscriptionRNA polymerase binds to DNA and
separates the strandsRNA polymerase uses one strand to
serve as a template to create a strand of RNA
RNA polymerase only binds to regions of DNA called promoters (landing pad)
The RNA is next edited, removing the introns, while leaving the exons (exons=expressed)
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RNA Splicing
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TranslationProteins are made by joining amino acids
(1 of 20) into long chains (polypeptides)◦How do 4 letters lead to so many
different amino acids?◦Read 3 letters at a time, called a codon◦UCGCACGGU◦UCG-CAC-GCU◦Serine-Histidine-Glycine◦Some codons code for the same amino
acid◦AUG is the start codon
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TranslationCodon – 3 nucleotides that code for an
amino acid. Found on the mRNA.Anticodon - Fit the codon. Found on
the tRNA
DNA: master plan; never brought to work site
mRNA: blue prints made from master plan
Ribosomes: building sitetRNA: trucks unloading materials
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Codons
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Codons
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Translation
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Transcription and Translation
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MutationsMutations – changes made in the genetic
material; can occur during copyingPoint mutation – effect only one
nucleotide. Frameshift mutation – an insertion or
deletion that effects the remaining string of nucleotides.
Chromosomal mutations – changes in the number or structure of chromosomes.
Polyploidy – when an organism has extra sets of chromosomes.
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MutationsTHE FAT CAT ATE THE RAT
◦Delete H (Frameshift / deletion)TEF ATC ATA TET HER AT
◦Change H to L (Point mutation)TLE FAT CAT ATE THE RAT
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MutationsDNA: TAC GCA TGG AATRNA: AUG CGU ACC UUAAA: Met Arg Thr Leu
◦SubstitutionDNA: TAC GTA TGG AATRNA: AUG CAU ACC UUAAA: Met His Thr Leu
◦ InsertionDNA: TAT CGC ATG GAA TRNA: AUA GCG UAC CUU AAA: Ile Ala Tyr Leu