Lecture 8 Flashcards Preview

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Flashcards in Lecture 8 Deck (86):
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Genetics

science of heredity

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Molecular biology

science of dealing with DNA and protein synthesis

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Genome

total DNA contained within the cell, consists of chromosomes and any plasmids present

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Genes are contained on ..

chromosomes

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Genes are..

sections of DNA that code for a functional product

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DNA is the..

macromolecule which is composed of nucleotides

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Nucleotides of DNA are composed of

-nitrogenous base
-deoxyribose sugar
-phosphate group

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4 types of nitrogenous bases in DNA

-adenine
-guanine
-cytosine
-thymine

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Prime

used to located the carbon on the pentose sugar

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Double helix

two strands of DNA are held together by H bonds in between bases

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Hydrogen bonds always occur in between..

specific bases, known as base pairing

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Adenine pairs with.. via..

thymine; 2 hydrogen bonds

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Guanine pairs with... via

cytosine; 3 hydrogen bonds (more H bonds in bacteria who withstand more heat, harder to break)

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Strands of DNA are..

complementary to one another

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The sequence of one strand (parent strand) determines

sequence of another. (ex: 5’ACTGATT3’
3’TGACTAA5’)

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The adjacent nucleotides are linked together by...

covalent phosphodiester bonds (sugar phosphate backbone)

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Carbon #5 of one nucleotide is joined to..

carbon #3 of the next nucleotides

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DNA is referred to as occurring..

from 5' to 3'

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Flow of genetic information

-DNA replicates before division so that each offspring receives one complete copy of genome
-DNA is used within the cell to make proteins
-DNA can flow between 2 diff bacterial cells (recombination)

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DNA replication

one parental double stranded DNA molecule is used to make 2 identical double stranded DNA molecules

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Since the DNA strands in DNA replication are complementary...

one strand of DNA can serve as a template for synthesis of other strand.

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Replication fork

small segment of sDNA unwinds and strand separate

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Each separated strand serves as..

a template for synthesis of a complimentary strand

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What enzymes are responsible for unwinding and separating the two DNA strands

DNA gyrase and helicase (first step)

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DNA gyrase

is found only in bacteria and NOT in eukaryotic cells therefore it serves as an antibiotic target

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Helicase

pulls the strand aport making it not its helix

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A short RNA primer is synthesized by the enzyme..

primase

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The primer serves as an..

attachment point for new nucleotides in order to form the new strand of DNA (second step)

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DNA synthesis occurs by the enzyme ..

DNA polymerase (third step)

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Nucleotides are placed..

in the correct order based on the sequence of the parent strand

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DNA polymerase

links the nucleotides together with phosphodiester bonds

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What type of bonds form in between new strand of parent strand linking them together

hydrogen bonds

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DNA polymerase can only add nucleotides in..

one direction, 5' to 3' and template must be read in 3' to 5'

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Synthesis of the first stand is..

continuous and known as leading strand

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Synthesis of the second strand is..

discontinuous and is known as the lagging strand

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Lagging strand synthesis

slower and more laborious than leading strand synthesis, must be made in the 3' to 5' direction

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DNA polymerase synthesized small fragments of DNA called..

okazaki fragments (made in 5' to 3' direction)

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Okazaki fragments are joined together by..

the enzyme DNA ligase

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In RNA what is different than DNA

ribose not deoxyribose and uracil not thymine

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Transcription

synthesis of a complementary strand of RNA from a DNA template

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3 types of RNA

-messenger RNA (mRNA)
-ribosomal RNA (rRNA)
-transfer RNA (tRNA)

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Messenger RNA

carry the coded info for making specific proteins, will directly form protein synthesis

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Ribosomal RNA

form part of ribosomes which are where protein synthesis occurs. gets put into pieces of a protein, once assembled won't go on and become a protein

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Transfer RNA

carry specific AA tot he ribosomes in order to make proteins. shuttle for AA, never turns into a protein

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Transcription requires

-enzyme: RNA polymerase
-a supply of RNA nucleotides
-a DNA template

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Steps in transcription

1. RNA polymerase binds to DNA at a specific site-promoter
2. RNA polymerase assembles nucleotides into a new RNA chain
3. RNA polymerase moves along templater as the new RNA chain grows
4. RNA polymerase reaches the end of the gene-terminator
5. RNA polymerase and newly formed single stranded RNA are released

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Purpose of transcription

mRNA serves as a short term copy of the gene that can be used to direct protein synthesis, rRNA and tRNA assist with the process of protein synthesis

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Translation

information in mRNA is translated in order to make proteins (codons)

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Codons

info from mRNA which is a group of 3 nucleotides

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Each codon is containing 3 nucleotides specifies a..

certain amino acid

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How many codons? how many stop codons>

64 codons, 3 stop codons

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Amino acids are..

redundant, while there are more than one way you can create an amino acid

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tRNA

is cloverleaf shape with anticodon of the tRNA

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What codons are the stop codons (nonsense codons)

UAG, UAA, UGA. signal end of translation

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Translation steps

1. mRNA attached to the ribosome
2. tRNA carrying the correct amino acid enters the ribosome and binds to the mRNA
3. the next tRNA with the amino acid enters the ribosome and binds to the mRNA (e site=exit)
4. 2 amino acids are joined by a peptide bond
5. ribosome moves down mRNA 5’to 3’ direction and and steps 3-4 are repeated until a stop codon is reached
6. mRNA and protein are released from the ribosome

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Mutation

change in the nucleotide sequence of DNA, this change may cause a change in a protein encoded by a gene

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Types of mutation

-point mutation
-frameshift mutation

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Point mutation

substitution, a single nucleotide is replaced by another nucleotide

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When DNA replicates is results in..

a substitution base pair

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Missense mutation

when DNA is transcribed and translated, an incorrect base can result in an incorrect aa in the protein

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2 frameshift mutations

-insertion
-deletion

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Insertion

additional nucleotide is added

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Deletion

nucleotide is removed

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Frameshift mutation

change the reading frame of the mRNA, sequence of most of the protein is changed downstream from the mutation

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Truncated proteins

stop codons may also be introduced prematurely as a result leading to short proteins

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2 ways mutations occur

-spontaneous mutations
-mutations due to mutagens

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Spontaneous mutations

occur due to occasional mistakes during DNA replication, occur in absence of mutagens

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Mutations due to mutagens

occur because of agents which work to bring about mutations in DNA (UV light, radiation)

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Regardless of the origin, mutations can result in..

-impomlete truncated proteins which are usually non functional
-protein with a diff sequence which will then have either a diff function or normal function
-silent mutation which has no effect on the protein (functional protein)

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Plasmids

self-replicating double stranded DNA molecules, contain genes which are non-essential such as those encoding resistance to penicillin

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F plasmids

F-factor or fertility plasmid, carry genes to make F pili, involved in bacterial mating

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F pili also allows for the..

transfer of genetic material in between

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R plasmids

resistance factors, carry genes for antibiotic resistance

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Vir plasmids

virulence factors, carry genes for toxin production, ability to cause diseases

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Horizontal gene transfer

DNA is transferred to other bacterial cells rather than to progeny

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Transformation

this is uptake of naked DNA pieces by a bacterial cell, DNA can come from dead cels or from released plasmids

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Recombination

pieces can be integrated into the chromosome

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Conjugation

bacterial mating, F plus allows the attachment of the F+ cell to the F- cell

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Male cell for conjugation

has an F pili referred to as F+ donor

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Female cell conjugation

does not have an F pili and is referred to as F- recipient

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A copy of the F plasmid can be..

passed through a hollow tube to the F- cell

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F- recipient cell now becomes..

an F+ cell

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Transduction

small fragments of DNA are transferred in between bacteria by a virus (bacteriophages)

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Bacteriophages

viruses that infect bacteria

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Steps in tranduction

-phage attached tot he bacterial cell wall and injects its DNA into the cell
-phage DNA is replicated within the bacterial cell
-phage DNA directs protein synthesis in order to make new phage
-new phages are assembled
-the "accident" phage can infect another bacterial cell
-DNA can now be incorporated into bacterial chromosome

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In transduction pieces of bacterial DNA are..

accidentally packaged into phage protein coats