Storage and Retrieval of Genetic Information + The genome and its transmission Flashcards
What are the similarities between DNA and RNA
Both are polynucleotides
both have a sugar-phosphate backbone formed of phosphodiester bonds
both contain adenine guanine and cytosine nitrogen contain bases
Outline the Structure of DNA
Doubles stranded helix with two antiparallel strands
sugar phosphate backbone
contains deoxyribose H atom of 2’ carbon (more stable than OH on RNA)
Contains Thymine as well as A,C,G
Has H bonding between complimentary base pairs. (A-T=2) (C-G=3) Pyrimidines (1C ring) bind to purines (2 C ring) maintains the diameter and stability of double helix
RNA strucutre
Single stranded
can have sections where the strand folds and forms double stranded segments held in place by H bonds
made up of ribose contains a OH group on 2’ carbon
lot less stable prone to cleavage in aqueous environments
Doesn’t contain thymine instead contains uracil
How much of the human genome is coding vs non coding
Majority of human genome is non coding
genes constitute around 2%
What are Repeat elements?
Non coding DNA
LINE and SINE elements can be used to detect polymorphisms for DNA fingerprinting
What are gene regulatory elements?
premotor and enhancer regions on the DNA
What are promotor regions on the DNA?
found usually immediately upstream of gene this is known as the TATA Box
Specific transcription factors will bind to the specific sequences on the DNA in this region and either augment or suppress gene transcription through activation or deactivation of RNA polymerase II
What are enhancer regions of DNA?
Other regulatory elements than can be found scattered before after or even in the introns of genes
Specific transcription factors bind to these specific regions and together form an committee that ultimately decides whether to augment or suppress transcription of a gene (this is regulated by the environment)
What are the two components of genes
Introns (intervening) non coding sections of DNA
Exons (expressed) coding sections of DNA
What are the other types of repeat sequences that make up the genome?
Satellite DNA –> tandem repeats of neuclotides found in the DNA
mini-satellite = highly polymorphic up to 1000 copies in one block
micro-satellite= small arrays of simple sequence repeats usually in introns
What is the function satellite DNA
has a role in at the telomere helping to prevent enzymatic attack
has a role at the centromere forms the structural non coding scaffolding
What are some issues that occur due to micro and mini satellite DNA repeats
Large scale duplication/deletion between homologous chromosomes
Translocation of DNA between non-homologous chromosomes
Microsatellites in coding regions can cause protein misfolding and aggregations in the cell
What is the process of DNA replication?
Why is it called this?
Semiconservative replication
each polynucleotide strand acts as a template for the synthesis of a complementary template strand
each DNA molecule has one original and one newly synthesised strand
What must be preset for DNA to be able to replicate?
dNTP’s (deoxyribonuclotide triphosphates dATP, dGTP etc)
various enzymes DNA polymerase DNA ligase
Outline the process of Semiconservative replication
Histone coat removed
section of DNA to be synthesised is unwound by DNA helicase (H bonds between complimentary base pears break )
On the leading strand dNTP’s form H bonds with complimentary bases
An RNA primase must first make a short section of RNA that allows the DNA polymerase to attach and start synthesising the new strand.
DNA polymerase moves in the 3’ to 5’ direction and joins adjacent nucleotides together via phosphodiester bonds DNA polymerase is rapid.
DNA polymerase only works in one direction synthesising the new strand in the 5’to 3’ direction (i.e. reads the 3’ to 5’ but makes in the 5’ to 3’) therefore on the lagging strand:
RNA primase (that also works in the 5’ to 3’ direction) initially makes small attachment units
This allows DNA polymerase attachment and synthesis of small sections in the 5’ to 3’ direction this leaves gaps behind it
These fragments are known as Okazaki fragments and have then got to be joined via DNA ligase.
What direction does DNA polymerase work in?
DNA polymerase only works in one direction synthesising the new strand in the 5’to 3’ direction (i.e. reads the 3’ to 5’ but makes in the 5’ to 3’)
What is and why is DNA polymerases proof reading ability essential?
Has a proofreading ability can stop if there is a change in diameter indicting bases haven’t paired correctly can go back and excise the incorrect base and swap it for the right dNTP.
ensures that there are no mutations in the DNA that could lead to the production of faulty proteins
Decreases the risk of deregulated cell proliferation
How are how chromosome replicated?
To initially start SCR must have binding of initiator protein to the DNA this forms a replication bubble allowing replication from the inside out (2 replication forks going in opposite directions from one bubble)
There are multiple of these bubbles making the process rapid
Where does transcription occur and what is required for it to occur
occurs in the nucleoplasm
must have and accessible DNA template strand
must have nucleoside triphosphates NTP’s present (CTP,ATP,GTP,UTP)
RNA polymerase II must also be present
Outline the process of transcription
Gene must be exposed via the binding of initiator proteins for form a replication bubble and expose the template strands
RNA polymerase only works in the 5’ to 3’ direction therefore bind to the leading DNA template strand
NTP’s diffuse and pair with complimentary bases and RNA polymerase II joins adjacent nucleotides synthesising a RNS strand in the 5’ to 3’ direction
co-transcriptional modification of RNA
binding of a splicesome
carriers out RNA splicing takes out the introns and leaves the coding exons
Alternative splicing may occur that allows multiple proteins to produced from one gene through rearrangement of exons
Translation where does it occur what must be present?
mRNA must successfully leave the nucleus
occurs in the cytosol
Ribosomes must be present as well as tRNA
What is tRNA
adaptor molecule
hairpin shaped strand of RNA held in place by hydrogen bonds
has a specific anticodon complimentary to a triplet codon on the mRNA and carriers a specific amino acid on the top of the hairpin molecule
What can stop mRNA leaving the nucleus
has to pass through nuclear pore but this is highly selective
microRNA can be bound to an argonaut protein to from a RNA induced silencing complex that can bind to mRNA and prevent it leaving the nucleus
What is the process of translation?
mRNA leaves the neuclus and bind to a ribosome on the RER on the 5’ end
first tRNA complex with complimentary anitcodon binds via complimentary base pairing to the codon in the vacant peptidyl site
first tRNA complex will always carry methionine (AUG)
second tRNA complex binds to the amino-acyl binding site
A pertide bond is formed between the two adjacent amino acids (energy to do this comes from the hydrolysis of the ester bond between the tRNA and the amino acid)
this is catalysed by the enzyme present in the ribosome called peptidyl transferase
ribosome moves along the mRNA reading the next exposed mRNA codon kicks off empty tRNA to be recycled
continues until reaches a stop codon (UAA UAC UAG)
this causes ribosome detachment and PPC release
What is the initiation codon
What are the stop codons
AUG initiation codes for methionine
UAA, UAC, UGA are the stop codons
why is the genome said to be degenerate?
multiple codons code for the same amino acid
Why is all mRNA not translated into proteins?
some is used to produce tRNA and rRNA
some mRNA may not leave the nucleus microRNA associates with argonaute protein to form RNA induced silencing complex that binds to specific mRNA’s preventing their exit from the nucleus (ie regulatory function)
What is a chromosome
Single molecule of DNA
contains multiple genes arranged one after each other with non coding DNA between them
How is DNA packaged into chromosomes
DNA is wrapped around histones forming nucleosomes
these are packaged and condensed much further to form chromatin which is condensed even further into a chromosome
What is Euchromatin?
lightly packed DNA that allows for active transcription (allows gene regulatory proteins and RNA polymerase II to bind)
What is Heterochromatin?
What are the two types and functions
Densly packed DNA exists in active decondensed and inactive condensed forms
functions in gene regulation and integrity of chromosomes
can be constitutive always inactive and condensed found at centromers
or can be facultative has the potential to be activated and decondesed e.g. X chromosome inactivation
What is mitosis
Division of somatic diploid cells into 2 genetically identical diploid daughter cells
What is the function of mitosis
For growth and repair of damaged tissues
What are the key stages in mitosis?
Prophase pro-metaphase metaphase anaphase telophase cytokinesis
what is prophase?
chromosomes condense to classic X shape
centrosomes migrate to opposite pole microtubule fibres begin to form the spindle
nuclear envelope breaks down
What is pro-metaphase?
Spindle microtubules bind to chromosomes via kinetochores (each chromosome has two kinetochores facing in opposite directions and form around centromere
M phase checkpoint ensures all chromosomes are correctly attached to the spindle
What is Metaphase
Spindle fibres gather chromosomes on the equator forming the metaphase plate
tension on kinetochores
What is Anapase?
Rapid phase
tension causes microtubules to shorten
centromere splits sister chromatids pulled to opposite poles as spindle fibres retract
Polar microtubules elongate helping to push the poles of the cell apart
What is Telophase?
chromosomes reach opposite poles begin to uncoil and lengthen
spindle fibres disintegrate
nuclear membrane starts to reform
initiation of plasma membrane cleavage
What is Cytokinesis?
Equal division of the cytosol and organelles between the two daughter cells
membrane pinches off to two daughter cells in cleavage furrows
NOT part of mitosis technically
What is meiosis?
Production of 4 genetically variant haploid daughter cells
Function of meiosis
Gametogenesis and inducing genetic variation
How is genetic variation induced during meiosis?
Crossing over of non sister chromatids due to homologous chromosomes pairing via synapsis to form bivalents
chiasma is the point as which non sister chromatids cross. multiple crossing over events can occur
independent assortment of chromosomes in Met I
independent assortment of chromatids in Met II
Process of meiosis overview
Meiosis I = the reduction division homologous chromosomes pair and line up on the equator pulled to opposite poles due to retraction of spindle fibres and the pushing of polar spindle fibres
Meiosis II
Mitotic division
product 4 genetically variant haploid daughter cells
