ap bio unit 3.2 - replication, transcription, translation, and mutations

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The replication of DNA is

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14.1 Genes specify proteins via transcription and translation 14.2 Transcription is the DNA-directed synthesis of RNA 14.3 Eukaryotic cells modify RNA after transcription 14.4 Translation is the RNA-directed synthesis of a polypeptide 14.5 Mutations of one or a few nucleotides can affect protein structure and function

50 Terms

1

The replication of DNA is

semiconservative

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2

origin of replication

the area of DNA that replication begins at (has specific sequence of nucleotides that allows starting proteins to attach to)

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3

replication fork

the Y-shape formed by separating the two strands of DNA

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4

helicase is responsible for

unwinding the helix at the replication fork

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single-strand binding proteins

bind to unpaired DNA to keep the strands from pairing again

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topoisomerase

relieves strain caused by unwinding on/around replication fork (keeps DNA strands straight and avoids supercoiling)

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primer

is a sequence of 5 - 10 nucleotides made by primase; synthesis can’t start on its own and builds from the 3’ end of the primer

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DNA polymerase

synthesizes new DNA by attaching complementary base pairs to the template strands

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DNA ligase

joins phosphate backbones of fragments into a continuous strand

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10

Describe prokaryotic chromosomes

single, circular DNA molecule

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11

Describe eukaryotic chromosomes

linear DNA and many proteins

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12

levels of chromosome packing in eukaryotes

  1. DNA (double helix)

  2. proteins called histones (+ charge) bind to phosphate backbones of DNA (- charge)

  3. chromatin folds so histones form bead-like nucleosomes

  4. fold into chromatin fiber as histone tails interact with other nucleosomes

  5. fiber folds into “looped domains”

  6. looped domains coil into condensed chromosomes

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Interphase chromatin can be slightly condensed and packaged as well, called

heterochromatin, which is inaccessible to transcription because of its folding

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euchromatin

“true chromatin”, less compact and not condensed; able to be transcribed

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15

genes affect phenotypes by dictating the production of

polypeptides (that make up proteins)

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differences between RNA and DNA

  • ribose sugar instead of a deoxyribose sugar

  • contains uracil instead of thymine, which is less stable (and therefore unsustainable for DNA)

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transcription

the synthesis of RNA using DNA as a template

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translation

the synthesis of a polypeptide using info from mRNA, occurs at the ribosomes

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bacterial cells can begin translation while mRNA is still being transcribed because

they do not have nuclei

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20

central dogma

Crick’s theory stating genetic information flows in one direction: DNA —> RNA —> proteion

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21

how many nucleotides make up a unit of code that corresponds to an amino acid?

three (triplet code)

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22

compared to the template DNA strand, the RNA molecule is

complementary and antiparallel

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codon

a set of three nucleotides of DNA that codes for one amino acid

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why is the genetic code redundant but not ambiguous?

several codons may code for the same amino acid, but will only code for that amino acid

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how does genetic code support theories of evolution?

the genetic code is nearly universal, which suggests a shared common ancestor

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RNA polymerase

  • synthesizes RNA by attaching RNA nucleotides to template strand

  • assemble in 5’ to 3’ direction

  • able to start a chain from scratch (doesn’t need a primer like DNA polymerase)

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transcription unit

section of DNA transcribed

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phases of transcription

  1. initiation - RNA polymerase binds to the promoter (eukaryotes: transcription factors form a transcription initiation complex and help RNA polymerase bind and initiate)

  2. elongation - RNA polymerase reads DNA from 3’ to 5’ and synthesizes 5’ to 3’, adding bases to the 3’)

  3. termination

    1. bacteria - reaches a terminator sequence + releases the transcript w/out modification

    2. eukaryotes - proteins cut off RNA from polymerase at a transcribed signal + pre mRNA goes through modification

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modifications to eukaryotic pre mRNA

  • 5’ methyl cap attached to 5’ end

  • poly-A tail added to 3’ end

  • facilitate export of mRNA from nucleus + help protect RNA from hydrolytic enzymes

  • help mRNA attach to ribosomes

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RNA splicing

removal of RNA that was initially synthesized that occurs in the nucleus; non-coding sections are cut and not translated

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introns vs exons

introns are intervening sequences and are removed; exons are coding regions that are expressed

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alternative RNA splicing

exons from the same gene are arranged in different combos which = more possible proteins formed from the same transcription

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spliceosome

protein complex that removes introns, degrades them, and joins exons on either side of the intron together

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ribozyme

RNA molecules that function as enzymes

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where do amino acids added to the polypeptide come from?

in the cell’s cytoplasm or are taken in from surrounding solution

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the anticodon of tRNA complements the

codon on mRNA; corresponds to one type of amino acid

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what does a tRNA do after it has added its amino acid and exits the ribosome?

is reused and picks up another amino acid in the cytosol

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aminoacyl-tRNA synthases

enzymes that help the tRNA and its amino acid bind

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ribosomes contain these three binding sites used for translation:

  • P site - holds tRNA adding to the polypeptide

  • A site - holds the next tRNA in line

  • E site - discharges tRNA after amino acid has been deposited

  • polypeptide will exit through an exit tunnel

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the small subunit of the ribosome allows

attachment of mRNA

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ribosomes mainly rely on this for their structure and function

rRNA (ribosomal RNA, which act as ribozymes)

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phases of translation

  1. initiation - mRNA binds to small subunit and an initiator tRNA; mRNA is scanned until start codon so the initiator tRNA can bind to it

  2. elongation - mRNA is read from 5’ to 3’ and amino acids are added one by one; rRNA forms peptide bonds between amino acids of A and P site & removes bond to tRNA; tRNA is moved A —> P, P—> E

  3. termination - stop codon reaches A site and release factors hydrolyze bond between polypeptide and tRNA; polypeptide is released through exit tunnel

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post-translational modifications

chemical changes to amino acids, removal of amino acids, change to polypeptides length; must be modified to become functional proteins and do specific jobs

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point mutation

changes in a single nucleotide pair of a gene

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45

genetic disorders/hereditary diseases are

when mutations have adverse effects on the phenotype

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small-scale mutations include

  • single nucleotide-pair substitution - replacement of one base and its complement

  • insertion/deletion - addition or loss of nucleotide pairs in a gene

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silent mutation

are not harmful b/c of redundancy of genetic code/translate to the same amino acid

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missense mutation

mutations that change an amino acid to another

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nonsense mutation

codon for amino acid is changed into a stop codon, ending translation prematurely

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mutagen

physical or chemical agents that interact with DNA and can cause mutations (ex. X-rays, UV radiation, nucleotide analogs)

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