Chapter 9: Molecular Biology Flashcards
define photograph 51
- x-ray crystallography picture of DNA
- showed double-helix structure of DNA
- taken by Rosalind Franklin
what did Rosalind Franklin and Maurice Wilkins do
- used x-ray crystallography to study DNA structure
- photograph 51
- concluded DNA was composed on 2 antiparallel sugar-phosphate backbones with nitrogenous bases paired in the interior
- determined that DNA has a uniform diameter from purine and pyrimidine
what did James Watson and Francis Crick do
- developed double-helical model for DNA
- concluded there are 2 polynucleotide strands in antiparallel orientation
- determined the nitrogenous bases in the interior always paired with others; A paired with T; C paired with G
who won the nobel prize in 1962
- Watson
- Crick
- Wilkins
why didn’t Rosalind Franklin win the nobel prize in 1962
- she died before the prize was awarded
- died from ovarian cancer probably from exposure to radiation from her experiments
what did scientists think were inheritable features before it was discovered that it was DNA
- proteins
describe the timeline of the human genome project
- began 1990
- declared complete in 2003 with 92% of human genome
- entire genome complete in january 2022
what was the goal of the human genome project
- sequence all the nucleotides that make up human DNA
- identify, map, and sequence all of the genes
define the nucleotide adenine
- pairs with thymine
- double ringed purine
define the nucleotide guanine
- pairs with cytosine
- double ringed purine
define the nucleotide cytosine
- pairs with guanine
- single ringed pyrimidine
define the nucleotide thymine
- pairs with adenine
- single ringed pyrimidine
define the nucleotide uracil
- pairs with adenine in RNA
- single ringed pyrimidine
define complementary base pairs
- A pairs with T
- G pairs with C
define double helix
- two strands of DNA twist around each other
- uniform diameter
define phosphodiester backbone
- backbone of DNA
- made from phosphate group of one nucleotide and sugar molecule of another nucleotide
- covalently bonded
define histone
- protein that DNA wraps around
define nucleosome
- DNA wrapped around 8 histones
define chromatin
- DNA and proteins
- includes genes, regulatory elements
define chromosome
- condensed chromatin
define chromatid (sister chromatid)
- one half of a duplicated chromosome
define homologous chromosome
- paired chromosomes that carry the same genes
- one from each parent
define non-homologous/heterologous chromosome
- not in a pair
- do not have the same genes in the same place
define euchromatin
- loosely packed
- genetically active
- rich in genes used for transcription process
- found in inner nucleus
define heterochromatin
- tightly packed
- genetically inactive
- found in outer nucleus
describe the genes of a humans smallest chromosome
- chromosome 21
- contains 48 million base pairs
- measure 1.5 inches (40mm) long
describe the genome of E. coli
- 4 million base pairs
- measures 1mm
describe the total human genome
- 3 billion base pairs
- measures 6 feet
what bonds are between nucleotides
hydrogen bonds
how many hydrogen bonds are between adenine and thymine
2
how many hydrogen bonds are between guanine and cytosine
3
what are the 3 parts of nucleotides
- deoxyribose (5 C sugar)
- phosphate group
- nitrogenous base
way to remember which nucleotides are purines
- pure as gold
- adenine
- guanine
way to remember which nucleotides are pyrimidines
- cut the pie (py)
- cytosine
- thymine
describe the direction of antiparallel strand of DNA in the double-helix
- 5’ to 3’
- 5’: where phosphate is
- 3’: where sugar is
define the semi-conservative model of DNA replication
- each of the two strands that make double helix serve as a template from which a new complementary strand is copied
- one strand splits as two strands are made
define origin of replication
- where DNA begins to unwind
describe the number of origins of replication in prokaryotes vs eukaryotes
- prokaryotes: one origin
- eukaryotes: several origins
describe the chromosome structure in prokaryotes vs eukaryotes
- prokaryotes: one circular
- eukaryotes: several linear
describe the rate of replication in prokaryotes vs eukaryotes
- prokaryotes: 1000 nucleotides/sec
- eukaryotes: 50 to 100 nucleotides/sec
which cells have telomeres: prokaryotes or eukaryotes
- eukaryotes
- ends of linear chromosomes
is DNA replication exergonic/catabolic or endergonic/anabolic
- endergonic/anabolic
- takes a lot of energy to build DNA
where does energy come from for DNA replication
- ATP, GTP, TTP, CTP
how does the replication machinery know where to begin
- origin of replication
- identified by specific nucleotide sequences
how is the DNA unwound
helicase enzyme
how many replication forks are formed and which direction does the replication proceed
- 2 replication forks
- goes in both directions
is DNA replication conservative or semiconservative
- semiconservative
- parent double helix unwinds and each strand become template
- two DNA molecules are created from one
what are the limitations of DNA polymerase and how are those limitations overcome
- cannot intiate DNA synthesis
- solved with RNA primer
how does DNA polymerase add the first nucleotide
- where the RNA primer is
how is over-winding of the DNA polymerase prevented
topoisomerase
how many primers are needed on the leading and lagging strands
- leading: 1
- lagging: multiple
summarize the process of DNA replication
- DNA unwinds at the origin of replication
- new bases are added to the complementary parental strands; one new strand is made continuously while the other is made in pieces
- primers are removed and new DNA nucleotides are put in place
- backbone is sealed by DNA ligase
what direction is DNA read during replication
- read up
- from 3’ to 5’ end of parental strand
what direction is the new DNA strand written during replication
- write down
- from 5’ to 3’ end of new strand
which end of a DNA strand are nucleotides added to
3’ end of growing strand
define leading strand
- new strand being replicated that is continuously synthesized
- doesn’t need to stop because it reads form 3’ to 5’
- top left, bottom right of diagram
define lagging strand
- new strand being replicated that is discontinuously synthesized
- stops and leap frogs; if not it would read in wrong direction from 5’ to 3’
- bottom left, top right on diagram
define helicase and it’s involvement in DNA replication
- unwinds DNA double helix at replication fork
define single-stranded binding proteins and their involvement in DNA replication
- prevent DNA from refolding into double helix
- stabilizes DNA strands
define topoisomerase and it’s involvement in DNA replication
- prevents DNA from overwinding on the ends
- ahead of replication fork
- breaking, swiveling, and rejoingin DNA strands
define primase and it’s involvement in DNA replication
- make RNA primers
- at 5’ end of leading strand
- at 5’ end of each okazaki fragment in lagging strand
define DNA polymerase 3 and it’s involvement in DNA replication
- read template strand and synthesizes new strand
- adds nucleotides to RNA primer or pre-existing DNA strand
define DNA polymerase 1 and it’s involvement in DNA replication
- replaces RNA bases from RNA primers with DNA bases
define DNA ligase and it’s involvement in DNA replication
- fixes gap in phosphodiester backbone
- joins okazaki fragments of lagging strand
- joins 3’ end of leading stand that replaces primer to the rest of the leading strand
define RNA primers and their involvement in DNA replication
- RNA nucleotides put down to help DNA polymerase know where to start
- short sequence of RNA bases
- made by enzyme primase
define okazaki fragments
- fragments made on lagging strand of DNA
what is a problem in eukaryotic DNA replication; explain the effects on the leading strand and the lagging strand
- chromosomes are linear so DNA replication reaches an end
- leading strand: synthesis continues until the end of the chromosome
- lagging strand: no place for primer to be made for the end segment to be copied so the ends remain single-stranded (unpaired)
how do cells overcome the problem of DNA replication in the lagging strand leaving a portion unpaired
- telomeres at the ends of chromosomes
- heterochromatin
- repetitive sequence that doesn’t code for a gene
- there is small loss over time in the sequences as DNA continues to replicate
what is the sequence in telomeres in humans and how many times is it repeated
- TTAGGG
- repeated 100 to 1000 times in each chromosome
what does the small loss in sequences of telomeres potentially cause
- aging
describe the process of telomere replication
- there is missing replication of DNA on the lagging strand
- telomerase extends the unreplicated end
- DNA polymerase can complete the replication of the lagging strand
define DNA proofreading
- DNA polymerase can make mistakes while adding nucleotides but it also proofreads every new base as it moves along
- detects incorrect bases, removes them, and replaces them with the correct bases
define mismatch repair
- mismatch repairs enzymes recognize incorrect bases AFTER replication
- excises incorrect base and replaces it
define nucleotide excision repair
- DNA double strand is unwound after replication
- incorrect bases are removed by enzyme nuclease as well as a few others on each side of the mistake
- DNA polymerase repairs the hole with the correct bases
- DNA ligase forms final phosphodiester bond
define thymine dimers
- two thymines forming a bond on the same strand of DNA
- usually caused by UV light
- fixed by nucleotide excision repair
define the central dogma
- process from DNA to RNA to proteins
- cellular chain of command that dictates the flow of genetic information
- DNA transcribed to mRNA translated to proteins
define transcription
- synthesis of RNA under direction of DNA
- produces mRNA: template for translation
define translation
- synthesis of a polypeptide occurring under the direction of mRNA
- occurs in ribosomes
define gene expression
- process by which DNA directs protein synthesis
- includes transcription and translation
does all DNA and all genes code for a product
- no
where does DNA transcription take place
- nucleus
where does mRNA translation take place
- ribosomes in the cytoplasm
are proteins functional right after being made
- no
- must be folded in endoplasmic reticulum and packaged in golgi apparatus
define non-protein coding genes and give an example
- genes that don’t code for a protein
- functional RNAs: tRNA that carries amino acids
are non-protein coding genes like functional RNAs transcribed, translated, or both
- transcribed but not translated
what is special about transcription and translation in prokaryotic cells
- have no nucleus so both take place in the cytoplasm
- transcription and translation can happen at the same time
define operons
- only in prokaryotes
- transcribed regions that include more than one gene
- cluster of genes with similar functions under the control of a single promoter
define the lac operon
- set of genes that makes all proteins needed to take in and break down lactose
define the one gene-one enzyme hypothesis
- original thought behind transcription and translation
- each gene codes for one enzyme
what four things disprove the one gene-one enzyme hypothesis
- many genes encode for proteins other than enzymes: transport, signaling, structural proteins
- some genes only encode for part of a protein
- some genes encode for non-coding RNAs: rRNA, tRNA, etc
- many genes have more than 1 exon and are processed differently to produce multiple products
describe the smallest gene in the human genome
- SRY gene
- determines male characteristics: on Y chromosome
- has 828 nucleotides and makes 204 amino acids
define transcription factors
- proteins that bind to the promoter region of the gene to be transcribed
- recruit RNA polymerase and bind with it to form initiation complex
define promoter
- region of DNA where transcription is initiated
define RNA polymerase
- enzyme that transcribes DNA into mRNA
- catalyzes process of transcription
- synthesizes RNA in a 5’ to 3’ direction (read up, write down)
define non-template DNA
- coding strand
- DNA strand that is not being transcribed
- will have similar sequence to the new RNA strand
define template DNA
- strand of DNA being transcribed
- strand that mRNA is based off of in transcription
- will have opposite bases as mRNA
define RNA transcript
- mRNA that is made from transcription
define transcription initiation
- transcription factors bind to promoter region of the gene to be transcribed
- transcription factors recruit RNA polymerase and bind with it to form initiation complex
- RNA polymerase recognizes start sequence and begins synthesizing RNA transcript in 5’ to 3’ direction
define transcription elongation
- RNA polymerase unwinds the DNA (10 to 20 bases at a time)
- RNA polymerase reads the DNA on the template strand and attaches the complementary RNA nucleotide
- the RNA nucleotide is joined to the pervious one on the 3’ end (of the RNA) via a phosphodiester bond along the backbone
define transcription termination
- RNA polymerase reaches and transcribes the termination sequence
- the RNA transcript is released by RNA polymerase
- RNA polymerase detaches from the DNA officially ending transcription
define polyadenylation sequence
- termination sequence in eukaryotic cells
- AAUAAA
define post-transcriptional pre-mRNA processing
- modifications to mRNA before it can be translated in eukaryotic cells
- modifications: 5’ capping, poly A tail addition, RNA splicing
describe the difference between DNA polymerase and RNA polymerase
- DNA polymerase: makes DNA during DNA replication
- RNA polymerase: make RNA during transcription
why does transcription not require ssb proteins to prevent rewinding of the DNA
- RNA polymerase only unwinds 10 to 20 bases at a time
- small section has little chance of rewinding
what are the RNA complementary bases to DNA bases (formatted DNA-RNA)
- A-U
- T-A
- G-C
- C-G
how is transcription termination different in prokaryotes and eukaryotes
- prokaryotes: RNA is immediately ready for translation or transcription and translation can happen at the same time
- eukaryotes: RNA reads special termination sequence called polyadenylation sequence (AAUAAA); mRNA is bound by proteins and needs additional processes
what are 2 unique features of prokaryotic gene expression
- happens solely in the cytoplasm
- RNA transcript does not need modification
how do the unique features of prokaryotic transcription affect gene expression
- multiple RNA polymerases can transcribe a single gene at the same time
- multiple ribosomes can simultaneously translate mRNA transcripts
where and when does post-transcriptional pre-mRNA processing take place
- in the nucleus
- after transcription, before translation
define exons and introns
- only in eukaryotic cells
- exons: coding sequences
- introns: non-coding sequences
what is removed in RNA splicing
- introns
- sometimes exons: creates different proteins from the same gene
what is the 5’ and 3’ end of the RNA transcript capped with during modification
- 5’: guanine nucleotide
- 3’: multiple adenine nucleotides
explain the relationship between the amount of genes and proteins a person has
- more proteins than genes
- multiple proteins can be made from one gene due to RNA splicing modification
what is the size of the human genome
- 3000 genes
define mRNAs (messenger RNAs)
- directs recruitment of tRNA molecules and production of the polypeptide
- determines sequences of amino acids in polypeptide
- binds to the small ribosomal subunit
define tRNAs (transfer RNAs): what 4 things do they all have
- carry specific amino acid on one end
- includes anticodon
- single RNA strand about 80 nucleotides long that folds into classic tRNA shape
- utilizes specific aminoacyl tRNA-synthetase to attach its amino acid
define anticodon
- 3 complementary nucleotides on tRNA
define aminoacyl-tRNA synthetase
- enzyme on tRNA that attaches a specific amino acid
define ribosome (in translation)
- reads mRNA and produces corresponding polypeptide
- made of proteins and rRNA
- has 2 subunits
- has 3 binding sites for tRNAs
define a site (aminoacyl-tRNA binding site)
- on large ribosomal subunit
- where all tRNA after 1st enter and bind to codon of mRNA
define p site (peptidyl-tRNA binding site)
- on large ribosomal subunit
- where 1st tRNA enters
- forms peptide bond between amino acid in p site and a site
define e site (exit site)
- on large ribosomal subunit
- where tRNA goes after adding amino acid to polypeptide chain
- where tRNA exits ribosome
define genetic code and why it’s known as conserved and redundant
- nucleotide triplets; RNA codon table
- conserved: bases make the same amino acids across all species
- redundant: repetitive; multiple codons can code for the same amino acid
what are the 4 components of translation
- ribosome
- transfer RNA
- messenger RNA
- polypeptide
what is the breakdown of what ribosomes are made of
- 1/3 protein
- 2/3 rRNA
what are the 2 subunits of a ribosome and what are their purposes
- small subunit: decodes genetic message (mRNA)
- large subunit: catalyzes peptide bond formation
what are the 3 tRNA binding sites on ribosomes
- E
- P
- A
which binding site on ribosomes do tRNA enter
- a site
- first tRNA enters at p site
describe how mRNA is read during translation, including the start codon
- read in 3 base codon fashion
- read 5’ to 3’
- each codon on mRNA interacts with anticodon on tRNA
- start codon always AUG on mRNA
what is the product of translation
- polypeptide
how are polypeptides produced in translation
- amino acids bonded together through interaction of tRNA on p site and tRNA on a site
what type of bonds are formed during translation
- peptide bonds
- covalent
how are transcription and translation different in regards to how strands are read
- transcription: read 3’ to 5’
- translation: read 5’ to 3’
how is the genetic code decoded
- translation
- nucleotides decoded/translated into amino acids
what are the 3 stop codons
- UAA (u are annoying)
- UGA (u go away)
- UAG (u are gone)
what animo acid does the start codon (AUG) code for
- methionine
does the stop codon code for an amino acid
- no
what is the reading frame
- determined by the first codon (AUG on mRNA)
- sequence of 3 bases read at a time
describe translation initiation
- mRNA binds to small ribosomal subunit
- start codon (AUG) is located
- initiator tRNA binds to start codon at p site
- energy is used to recruit and bind the large ribosomal subunit
describe translation elongation
- tRNA enters the a site and bonds to corresponding codon of mRNA
- peptide bond formed between chain of amino acids at p site and new amino acid at a site
- mRNA is shifted causing tRNAs to shift sites: tRNA at p site breaks its bond with mRNA and breaks away through e site; tRNA at a site shifted to p site and is attached to growing polypeptide chain
describe translation termination
- stop codon in mRNA is recognized (UAA, UGA, UAG)
- release factor is recruited and binds to stop codon causing hydrolysis of polypeptide from tRNA
- energy utilized to cause dissociation of translation components
what happens to the polypeptide chain after translation
- goes to endoplasmic reticulum to be folded
- taken to golgi apparatus to be processed and transported
define gene expression
- process of “turning on” a gene to produce RNA and proteins
- done through stopping transcription or translation
why are genes regulated
- to control timing, location, and amount of gene expression
do all cells need to express all genes
- no
how are genes regulated in prokaryotes
- almost entirely through transcription
- because transcription and translation can happen simultaneously, transcription must be stopped so gene isn’t automatically translated
how are genes regulated in eukaryotes
- multiple levels:
- epigenetic
- transcriptional
- post-transcriptional
- translational
- post-translational
define epigenetic
- one gene affects regulation of another gene