Unit 2- DNA and Gene Expression Flashcards
Whose studies determined that DNA was the genetic material instead of Protein?
Griffin, Hershey and Chase
Whose Research is this? What was the impact?
Griffith. He determined that DNA was the heritbale information in DNA because it was changed and reverted back to its original form.
Whose work was this? What was the impact?
Hershey and Chase
Who determined the structure and mechanism of replication of DNA?
Watson & Crick
Rosalind Franklin & Wilkins
Building Blocks of DNA
Nucleotides
Components of a Nucelotide
Deoxyribose
Phosphate
Nitrogenous Base (4 Different Types)
Polarity of DNA
5’->3’
Base Pairs in DNA
A:T G:C
How many base pairs are in each turn of the Double helix?
10
DNA Strands run _____ To each other
Antiparallel
How much DNA is in a human cell
2m of DNA
How large is a typical Cell?
20-40 Micrometers
Packaged DNA consists of
Single Molecule of DNA+Associated Packaging proteins (Histones)+ Scaffolding Proteins
Bacteria typically have _____, _____ chromosome.
Single, Circular
Name This Image
Karyotype
Each Chromosome is made up of
Single, long DNA Molecule+accompanying proteins (Chromatin)
Karyotypes are arranged in what pattern?
From largest to smallest, except the sex chromosomes, which are always #23
Functions of Chromosomes:
To Carry Genes
Replication Origin
Sites Where Replication begins
Telomeres
help overcome the End-Replication problem
During Mitosos, DNA is compacted to what size?
~ 10,000-75000x
During Interphase, DNA is compacted to what size?
~500-400x ( Less compacted than in mitosis)
Nucleosome
Basic Unit of Eukaryotic Chromosomes that consist of a length of DNA coiled around a core of histones.
Histone core of nucleosomes are made of
4 different Histone proteins
What is the function of Linker Histone H1
Helps pack nucleosome cores more tightly
Levels of Chromosome Packing
DNA-> Nucleosomes
Nucleosomes (beads on a string) packaged into Chromatin Fiber
Chromatin Fiber packaged into folded loops
Folded loops packaged into Mitotic Chromosome
Chromatin-Remodeling Complexes
Use ATP to Change DNA POsition along Histone cores of nucleosome
Can make DNA More or less accessible
True or false: Chromatin-remodeling Complexes are actvated during mitosis
FALSE
Acetyl groups ___ chromatin, making it more accessible
Open
Histone Acetyl Transferases (HATs)
Add Acetyl Groups to Histones
Histone Deactylases (HDACs)
Remove Acetyl groups from histones
Specific combinations of modifications create docking sites for regulatory proteins that promote _______ or _______
Decondensation; condensation
Euchromatin
Regions or chromosome that are active and less condensed
Heterochromatin
Regions of chromosome that are not active and are more condensed
Regions of euchromatin and heterochromatin are regulated by what?
Histone Modifications
Histone Modifications promoting “Condense Me” signals may propagate along DNA until________ is reached
Barrier Sequence
Errors in Genetic code
Mutations
Mutations are a basis of
Evolutionary change
Each strand of DNA serves as a ______ _____ for new complementary strand to be replicated
Template Strand
The Human Genome can be replicated in as little as
8 Hours
Semiconservative Replication
Since one sister strand of new daughter DNA molecules is new and one is old, mechanism of replication is called semiconservative.
Describe this process
Semiconservative DNA Replication
True or False: DNA Replication begins at only one site along eukaryotic chromosomes?
False
Replication Origins
Special Sequences of DNA that recruit initiator proteins to begin DNA replication Process
Replication Machine
The DNA Double Helix is opened and more proteins are recruited
Replication Fork
Y-Shaped Region along which new DNA strands are synthesized
Bidirectional replication
Since replication proceeds in both directions away from the replicaiton origin, the process is bidirectional.
Polymerization
Occurs by addition of nucleotide to 3’ end of growing DNA molecule and 5’ end of incoming nucleotide (Continues to grow in 5’ to 3’ direction)
DNA is replicated in opposite directions causing 1 strand to be ______ and another strand to be ______
Continuous ; Discontinuous
Or
Leading;Lagging
How is the discontinuously replicated strand produced?
Via Backstitching mechanism that allows for unidirectional addition of DNA Nucleotides in an overall bidirectional process
The continuously replicated strand is called the
Leading Strand
The discontinuously replicated strand is called the
Lagging strand
The small pieces of DNA replicated for discontinuous strand are called
Okazaki Fragments
True or False: Okazaki fragments remain disjointed.
FALSE: They are put together with DNA Ligase
What is the error rate of DNA Polymerase
~1 in 10^7 errors
How does DNA Polymerase maintain its low error rate (high fidelity)
Carefully monitoring base-pair before catalyzing nucleotide addition
Proofreading when mistake occurs
When does DNA Proofreading occur
Concurrently with DNA Synthesis
What does DNA Polymerase do if an error is detected?
The previously added base is removed and polymerase tries again
DNA Polymerase must attach to the 3’ end of the template before
placing nucleotides
True or false: Primase has proofreading
FALSE
True or False: Chromatin-remodeling complexes are activated during Mitosis
False
What is the function of Nuclease?
Degrades RNA Primer
What is the function of Repair polymerase?
Makes DNA version of complementary strand
What is the function of DNA Ligase?
It links Okazaki fragments together.
What are some of the enzymes and proteins that come together to complete DNA Replication?
DNA Ligase
Single-Stranded Binding proteins
DNA Topoisomerases
Primase
Polymerase
Sliding Clamp
Clamp Loader
Repair Polymerase
DNA Ligase
What is the DNA End-Replication Problem?
As the Replication fork reaches the end of the lagging strand, there is not enough room to replace the final primer with DNA.
Telomeres
Long, repetitive sequences at the end of chromosomes that solve the DNA-End replication problem
Telomerase
The enzyme that maintains telomeres. It has a short stretch of RNA incorporated into enzyme that serves as template for the telomeric DNA
What are the types of DNA Damage?
Deamination
Depurination
Covalent Modifications (Thymine Dimers)
What types of DNA damage would result in a Double-Stranded break?
Radiation
Mishap at replication fork
Chemical assaults
What is the basic tool for DNA damage Repair
Excision Repair
Name 4 mehtods for DNA damage repair
Excision Repair
Mismatch Repair
Nonhomologous End-Joining
Homologous Recombination
What are the steps in a Mismatch DNA Repair?
Mistake is recognized
new vs. parental strand is determined
Portion of mutated strand is removed
Filled in by repair polymerase
What is Non-Homologous End Joining?
Double-Stranded break repair that occurs soon after the damage occurs. The Enzymes detect damage, “clean” the ends, and ligate them together
True or False: NHEJ will result in loss of some nucleotides
True
What is Homologous Recombination
A Double-Stranded Break Repair which the 5’ ends of broken DNA are chewed back and DNA repair polymerase extends the broken strand.
What are the consequences of a lack of DNA Repair?
Mutation
Sickle-Cell Hemoglobin
Cancer
What is the Central Dogma of Molecular Biology?
DNA Serves as Template for RNA Production (transcription) and multiple RNAs function in making proteins (translation)
What is Gene Expression
Process whereby information in DNA is turned into useful product
True or False: The entire Genome is transcribed into RNA
False:
Entire genome is not transcribed into RNA and cell tightly controls how much of each type of RNA is made
What is the Nucleic Acid associated with RNA
Ribonucleotides (as opposed to Deoxyribonucleotides)
What are the Nucleotides associated with RNA (and their Base Pairs)
Adenine, Guanine, Cytosine, Uracil
True or False: RNA is Double-Stranded
False: RNA is single-Stranded
What are three types of functions that RNA’s single-stranded properties result in?
Structural, Catalytic, and Regulatory functions
True or False: Transcription uses Helicase to open the DNA Strand
False: The DNA is opened, but there is no Helicase involved.
True or False: RNA transcription has a higher fildelity than DNA replication
False
Messenger RNAs (mRNA) Function
Code for Proteins
Ribosomal RNAs (rRNAs) function
Form the core of the ribosome’s structure and catalyze protein synthesis
MicroRNAs (miRNAs) Function
Regulate Gene Expression
Transfer RNAs (tRNAs) function
Serves as adaptors between mRNA and Amino Acids during Protein Synthesis
Other Noncoding RNA Function
Used in RNA Splicing, gene regulation, telomere maintenance, and many other processes
Promoter’s DNA sequence directs RNA Polymerase as to which DNA strand (does what)??
Serves as Template
What are the three types of RNA Polymerases in Eukaryotes?
RNA Polymerase I
RNA Polymerase II
RNA Polymerase III
What genes are transcribed by RNA Polymerase I?
Most rRNA genes
What genes are transcribed by RNA Polymerase II?
All protein-coding genes, MiRNA genes, plus all the genes for other Noncoding RNAs (Spliceosome)
What genes are transcribed by RNA Polymerase III?
tRNA Genes
55 rRNA Genes
Genes for many other small RNAs
What process begins when TBP/TFIID complex binds the TATA box of a gene?
RNA Polymerase II Transcription
What is a TATA Box?
A region of ~25 Bases upstream of transcription start site, made of many T & A Nucleotides
What is the Transcription Initiation Complex?
When the Binding of TBP/TFIID recruits the remaining general transcription factors and RNA Polymerase II
TFIIH
A kinase that’s part of the Transcription Initiation Complex, which phosphorylates the tail of RNA Polymerase II
What 3 steps must be taken in order for the Pre-MRNA transcript to be processed into mRNA in the nucleus?
RNA Capping
Polyadenation
Splicing
What allows some processing proteins to assemble on RNA Polymerase II?
The Phosphorylation of the RNA Polymerase II Tail that allows this.
What is RNA Capping?
A Modified Guanine Nucleotide is added to the 5’ end of a transcript shortly after transcription begins
Helps protect from Endogenous Nucleases
Helps Get translation started
What is Polyadenation?
A sequence within a transcript that tells RNA Polymerase II when to stop.
(Poly-A Signal)
What are Introns?
Regions that are not expressed as protein
What are Exons?
Regions of a gene that are expressed as protein
True or false: The number and length of introns and exons remains consistent.
False: the number and length of introns and exons varies from gene to gene.
RNA Splicing:
When Introns are spliced out of pre-MRNA, leaving the Exons behind to code for the protein
True or False: Sequence within Exons and Introns dictates boundaries of introns
TRUE
What is a Spliceosome?
A compltex of small Nuclear RNAs (snRNAs) and associated proteins (snRNPs) that are responsible for removing some introns
True or False: All introns are spliced with the Spliceosome.
False: Some introns are spliced by the spliceosome, but others are self-splicing
What are some examples of Alterations in splicing?
Exon Skipped
Alternative Exons
Introns Skipped
After processing, where is mRNA going to be exported to?
The Cytoplasm
Proteins that bind the 5’ Cap, Poly-A Tail, and splice sites facilitate interaction with what area?
The Nuclear Pore Complexes.
mRNA Half-Life
The amount of time required for half the population of mRNA to be degraded
True or False: Every mRNA has the same Half-Life
False: Different mRNAs have different half-lives.
How is the mRNA’s Half-Life determined?
By Specific sequences within mRNA, usually within the Untranslated Regions (UTRs)
What is the end result of Translation?
Proteins
What is the process of utilizing information in mRNA to produce Protein?
Translation
What is the Genetic Code?
The 4 different nucleotides that encode the 20 Amino Acids in groups of Non-Overlapping, 3-letter words (Codons)
True or False: Each codon is non-specific
False: Each codon is specific
True or False: There is redundancy among many of the codons
TRUE
How does the cell know where to start Translation?
There must be a Kozak Sequence and an AUG Start Codon
What sets the reading frame for translation?
The Kozak sequence and the AUG Start codon
True or False: Each Eukaryotic mRNA has more than one reading frame.
FALSE: There is only one reading frame. Finding the correct AUG to start is how to find it.
What is a point mutation?
Addition, Deletion, or Substitution of a single base
What types of mutations are frameshift mutations?
Additions and Deletions
What type of mutatation Substitutes one Amino Acid Codon for another Amino Acid’s Codon
Missense Mutation
What type of Mutation substitutes an Amino Acid Codon with a Stop Codon
Nonsense Mutation
What type of mutation substitutes one Amino Acid Codon for the same Amino Acid Codon?
Silent Mutation
What type of mutation substitutes a Stop Codon with an Amino Acid Codon?
NonStop Mutation
When an Amino Acid is attached to a tRNA, what is it called
Aminoacyl-tRNA^AA
or
Charged tRNA
What shape are tRNAs typically in?
Cloverleaf shape
What are the two important sites (at opposite ends) of a tRNA molecule?
Anticodon
Amino Acid Attachment Site
What is tRNA Wobble?
It means there are not 61 different tRNAs in most species*
WWhat are the 20 specific enzymes that match the specific Amino Acid with a specific tRNA?
Aminoacyl-tRNA Synthetases
What is used to create the high-energy bond between tRNA and the Amino Acid?
ATP
What are Ribosomes made out of
rRNA and Proteins
What are the two subunits of a Ribosome called?
Large (60s)
Small (20s)
come together to make (80s) when the ribosome is active)
What organelle is responsible for the process of translation?
Ribosomes
True or False: the Ribosome moves along the mRNA 3 codons at a time?
FALSE: They move along the mRNA one codon (3 nucleotides) at a time.
What are the three Binding sites for tRNA on the Ribosome?
A, P, E Sites
What is the definition and function of the A site on the Ribosome?
Aminoacyl-tRNA Binding Site
Accepts incoming tRNA
What is the definition and function of the P site on the Ribosome?
Peptidyl-tRNA Binding Site
Holds tRNA that is being attached to the growing polypeptide
What is the definition and function of the E site on the Ribosome?
Exit site (same answer for both)
Describe the Process of Translation in steps:
tRNA holding growing polypetide sits in P site •
A site, which had been empty, accepts incoming tRNAAA
• Ribozyme activity of rRNA forms peptide bond between last AA of growing polypeptide and incoming AA •
This severs connection between P site AA and its tRNA and at the same time, releases energy to power this process •
Large subunit shifts forward, shifting spent tRNA to E site and tRNA from A site to P site •
A site ready for next charged tRNA •
Continues until stop codon reaches A site
What Amino acid would the initiator tRNA carry?
Methionine (MET)
What are TIFs?
Translation initiation Factors
A group of proteins necessary for translation initiation
What makes the initiator tRNA unique?
It is able to bind to the P site, whereas the others can only initially bind to the A site.
Kozak Sequence Example
ACCAUGG
What is the initiator tRNA in Bacteria?
tRNA^fMET (F-Methionine)
True or False: Bacteria have a 5’cap to mediate small subunit and mRNA interaction.
FALSE
What is a Shine-Delgarno Sequence?
occurs just upstream of the AUG in Bacteria. It base-pairs with rRNA nucleotides, this positioning initiator tRNA at the P site.
How many coding sequences can a bacterial mRNA have?
How many coding sequences can a Eukaryotic mRNA have?
What are the three STOP Codons?
UAG, UGA, UAA
What happens when a Stop codon enters the A site?
Translation Termination
What does the release factor protein do in Translation?
It binds to teh A site, causing Ribosomes to add water molecule to peptidyl tRNA, resulting in a relase of the polypeptide chain
What is a Polyribosome?
When a single mRNA is translated by multiple ribosomes simultaneously
What is the end result of turning genes on and off or regulating gene expression?
Cell Differentiation
Complexes of mRNA with several accompanying ribosomes are called?
Polyribosomes/Polysomes
How long do proteins last?
A few moments, minutes, hours, days, months, or years.
How are proteins recucled?
A process called proteolysis
Describe the Proteolysis process
Enzymes that break down proteins, called proteases, break peptide bonds in the proteins.
A large, cylindrical complex of proteins that perform proteolysis in Eukaryotes
Proteasome
What do the ends of Proteasomes do?
They unfold the incoming proteins and feed linear polypeptide chain into the interior of the complex.
Inside the Proteasome, what do proteases do?
They break the protein into its individual Amino Acids
How are proteins targeted to a proteasome?
Ubiquitin
What is Ubiquitin?
A small polypeptide that when covalently bonded to protein functions to target that protein to the proteasome
In order for target protein destruction to occur, what must first happen?
Several Ubiquition molecules must be added to the protein
A Sequence of Amino Acids that function in targeting the protein for destruction
Degron
What are the Ubiquitin linked to on the target polypeptide?
The Lysine Residues
True or False: All genes within an organism have different DNA?
False: They all have the same DNA
How do cells have different functions?
Because they turn particular genes on or off.
What controls gene expression?
Signals from outside the cell:
Hormones, Tension of Substratum
True or False: Different cells respond in different ways to various signals
TRUE
What is the major mechanism for Gene Expression control?
Control of Transcription
What is the function of a Promoter in transcription?
To bind key transcription factors and RNA Polymerase
What binds other transcription regulators that control what happens at the promoter?
Regulatory DNA Sequences
What are the functions of Regulatory DNA Sequences?
May act as simple switches or in more complex ways
Sequences can be thousands of nucleotides away from transcription start site
Located nearby in bacteria, may be far away (distal) in eukaryotes
True or False:
Transcriptional Regulators have DNA Binding domains and regions that interact very unspecifically and weakly.
FALSE:
They interact very specifically and strongly
What are Transcriptional Switches?
They are switch-like (on-off) and allow the cell to respond to environmental cues.
In bacteria, what are the two switches which control several regulated genes/proteins?
Tryptophan Operon
Lac Operon
The Lac Operon is a _____ reaction
Catabolic (Breaks down)
The Tryptophan Operon is a _____ reaction
Anabolic
Transcriptional Activators
When activated, they turn the genes on or activate them
Transcriptional repressors
When activated, they turn the gene off or repress them.
How does the Tryptophan Operon work?
When Tryptophan is low, the operon is turned on due to the absence of the repressor at the regulatory seqence
When is the Tryptophan Operon repressed?
When the concentration of Tryptophan increases.
What are the steps of the Tryptophan Operon Repression?
The free Tryptophan binds the repressor and activates it, allowing it to bind to the DNA.
Binding to regulatory sequence blocks RNA polymerase from binding the Operon’s promoter
Enzymes for tryptophan production are no longer expressed.
How does the Lac Operon work?
When Lactose is present and ATP is low, the Lac Operon will be turned On.
What operon controls the expression of genes required for breakdown of lactose to monosaccharides which can be used in cellular respiration?
Lac Operon
What are the differences between the Tryptophan and Lac Operons?
The Tryptophan is anabolic, Lac is catabolic
Tryptophan is controlled by a repressor, Lac has an activator and a repressor
Which Operon is controlled by an activator and a repressor?
Lac Operon
What is the Lac Operon’s Repressor Called? How does it work?
Lac Repressor;
Repressor binds regulatory DNA (Operator) and will result in no gene expression.
What is the Lac Operon’s Activator called? How does it work?
Cyclic AMP Activator (CAP Activator)
What is cAMP
Cyclic Adenosine Monophosphate
When is cAMP produced?
When ATP is low
When can the Cap Activator bind regulatory DNA?
Only if it is bound by cAMP
Once cAMP binds the CAP Activator, CAP binds DNA (at what site)_____ and can induce transription of the Lac Operon only if what?____
CAP Binding Site
Only if it is not repressed by the LAC repressor.
In the Lac Operon, if there is a high concentration of Glucose and Lactose, will the operon be off or on?
Off
In the Lac Operon, if there is a high concentration of Glucose and a low concentration of Lactose, will the operon be off or on?
Off
Lactose is required to turn the Operon On
If there is a low concentration of Glucose and a low concentration of Lactose, will the Lac Operon be On or Off?
Off.
Lactose is required to turn the Operon On.
In the Lac Operon, if there is a low concentration of Glucose and a high concentration of Lactose, will the operon be off or on?
On.
If there is Low Glucose, there is low ATP.
If there is low ATP, then cAMP is activated. The Lactose will bind the repressor to remove it and transcription will occur.
What are regulatory sequences called in Eukaryotes
Enhancers
Where are enhancers located?
They can be thousands of nucleotides away from the transcription start site.
True or False:
Enhancers can only be upstream from the Transcription Start Site
False:
They can be upstream or downstream of Transcription start site
What is located between the enhancer and the Transcription start site?
The Spacer DNA
Interaction of enhancer sequence with Mediator Protein complex facilitates what?
Eukaryotic Transcription
Define Pluripotent
capable of giving rise to several different cell types.
How can cells be induced to de-differentiate?
By manipulating which transcription regulators are active or inactive.
What are the results of a cell being de-differentiated?
It results in loss of cell identity and a cell that can be potentially induced to become any other cell (iPS)
What is the result of Epigenetic control of Gene Expression?
Differentiated cells stay differentiated and so do their daughter cells due to the modifications to their chromatin.
Epigenetic modifications lead to what?
Cell Memory- an ability of cells to recall which genes they should express or not
How is Epigenetic control of gene expression regulated/mediated?
By positive feedback loops in which master gene regulators impact their own gene expression:
Gene A induces the Expression of Gene A
What is DNA Methylation?
What is the result of DNA Methylation?
Addition of methyl group on specific DNA bases (cytosine) results in silencing of that gene
True or False:
DNA Methlyation patterns are not passed from one generation to the next.
FALSE:
DNA methylation patterns are passed from one cell generation to next, including gametes in some instances
How do histone modifications impact chromatin structure?
It can create Euchromatin ( loosely packed) or Heterochromatin (tightly packed) chromatin which can result in a loss of gene expression
True or false:
Histone Modifications are passed from parent (cell) to offspring (cell).
TRUE
Define Epigenetic Inheritance
It means that a parent’s experiences, in the form of epigenetic tags, can be passed down to future generations.
What is a method of Translational control in Prokaryotes?
Some bacteria express proteins that bind Shine-Delgarno sequence of prokaryotic mRNAs and thus block ribosome binding
What is a mechanism of Translational Control in Eukaryotes?
mRNAs may have regulatory sequences within their 5’UTR that impact 5’ cap from binding small ribosomal subunit
Define:
Nonsense-Mediated Decay
Nonsense mutation will cause premature termination of translation and an incomplete polypeptide chain
How do Eukaryotic cells use Nonsense-Mediated Decay?
Eukaryotic cells use nonsense-mediated decay to destroy mRNAs containing premature stop codons
In mammals, how are premature stop codons detected?
By the Exon Junction Complex (EJC)
When is the EJC Deposited?
Wherever intron is removed from pre-mRNA, so each spliced mRNA has at least one complex bound to it
If mRNA contains a stop codon prior to the final EJC, what happens?
Translation is terminated and EJC does not get knocked off the mRNA
Define Nonstop Decay in Eukaryotes
Translation stalls when the ribosome reaches the end of transcript that lacks a stop codon
Nonstop Decay (process)
RNA degrading enzyme binds empty A site of ribosome and degrades the defective mRNA
Define a nonstop decay in Bacteria
Transfer Messenger RNA (tmRNA) binds the A site and directs the addition of amino acids that target the protein for destruction
Regulatory RNAs are part of what RNA family?
The Noncoding RNA
What are the three types of Regulatory RNA found to regulate gene expression at the post-transcriptional level?
MicroRNAs (miRNAs)
Small Interfering RNAs (siRNAs)
Long Noncoding RNAs (lncRNAs)
How are Micro RNAs expressed?
As part of longer RNAs, sometimes as part of introns and exons of other mRNAs
True or False:
MicroRNAs (miRNAs) must be processed by Dicer)
True
Define RISC
RNA-Induced Silencing Complex
True or False:
MicroRNA (miRNAs) do not have to integrate with RISC in order to function.
False:
Must integrate with RISC (RNA-induced silencing complex) in order to function
How do MicroRNAs (miRNAs) function?
Base-pair with target mRNAs and inhibit expression of target
•Exact, complementary match = target mRNA for immediate destruction
High degree complementary match = sequestration in cell away from translation machinery, eventual degradation
True or False:
MicroRNAs (miRNAs) are an inefficient way to control several related genes.
FALSE:
It is very efficient because there are several targets possible if the mRNAs all share the target sequence, which would be ideal for targeting several related genes.
Describe this process
miRNA processing beginning in mRNA and ending in mRNA degrading or sequestering and eventual degrading.
What is the Cell’s defense mechanism that eliminates foreign RNAs (i.e. Viral RNAs)
RNA Interference (RNAi)
What is dsRNA?
Forms the genetic material of some viruses (double-stranded RNA viruses). Double-stranded RNA such as viral RNA or siRNA can trigger RNA interference in eukaryotes, as well as interferon response in vertebrates
How does Dicer process dsRNA?
It generates ssRNA ~22 base pieces (small interfering RNAs, siRNAs) which integrate with RISC and then target viral RNAs for destruction
What are siRNAs? what is their function?
Small Interfering RNAs, which integrate with RISC and then target viral RNAs for destruction
How many base pairs are LncRNAs?
At least 200 base Pairs Long
What are some of the functions of LncRNAs?
Some have been found to regulate gene expression
Xist binds one X chromosome in females and silences that specific chromosome (Barr body) by recruiting chromatin remodeling proteins
Various found to be produced from “wrong” DNA strand of target gene, generating antisense strand complementary to target
Inhibits translation and/or contributes to RNAi-mediated destruction of target
Describe this image:
DNA Space-Filling Model
Describe this image:
The Cell Cycle
Describe this image:
An Electron micrograph of Nucleosomes (Beads on a string)
Detail A-F of this image:
A: DNA Double Helix
B: Beads on a string form of Chromatin
C: Chromatin Fiber packed into Nucleosomes
D: Chromatin fiber folded into Loops
E: Entire Mitotic Chromosome
F: Each DNA Molecule has been packaged into a mitotic chromosome
Describe the process in this photo:
A linker histone helps to pull the nucleosomes together and pack them into a more compact chromatin fiber
Describe the processes occurring in this image:
Chromatin-Remodeling Complexes
Using ATP to change the position along the histone cores
Describe this image:
The variation of chromatin structure along an interphase chromosome
Describe the image:
Describe the image:
DNA Replication
Describe the image:
Semiconservative DNA Replication
Describe the image:
DNA Double Helix is opened at the replication Origin
Describe the image:
DNA synthesis at the Y-shaped Replication Fork
Describe the image:
Multiple Replication forks along the DNA
Describe the image:
DNA Polymerase adds a deoxyribonucleotide to the 3’ end of the growing DNA Chain.
Describe the image:
At each replication fork, the lagging strand is synthesized in pieces
Describe the process in the image:
DNA Polymerase proofreading
Describe the process in the image:
Okazaki fragments are synthesized and ligated to form a continuous strand.
Describe the image:
The replication machine
Describe the image:
DNA Topoisomerase relieves the tension that builds up in front of the replication fork (preventing double-stranded breaks)
Describe the image:
DNA End replication repair
Describe the image:
DNA telomeres and telomerase adjusting end-replication problem
Describe the image:
DNA Damage in the form of Depurinaton and Deamination
Describe the image:
Deamination leads to mutations
