A Level DNA & Genimics + Molecular Genetics Flashcards
(29 cards)
Define gene
- A sequence of nucleotides that code for 1 polypeptide
- A segment of DNA
- A unit of inheritance
Describe the structure of DNA (A level)
In a polynucleotide,
.
- Many nucleotides join tgt via phosphodiester bonds formed in a condensation rxcn
- btwn OH group on 3’ carbon and phosphate group on 5’ carbon
- With the removal of 1 pyrophosphate
- 5’ end of 1 polynucleotide chain has phosphate group on 5’ carbon
- 3’ end has OH group on 3’ carbon of sugar
- nucleotides consisting of 1 phosphate group, 1 nitrogenous base, and 1 pentose sugar
_______ _______ _______ _______
In 1 molecule of DNA:
- 2 polynucleotide chains twisted around each other in a double helix
- the 2 Polynucleotide strands run in anti-parallel directions (One in ‘5 to ‘3, the other in ‘3 to ‘5)
_______ _______ _______ _______
- DNA has uniformed width of 2nm same width of 3 rings of purine and pyrimidines
- Hydrophobic Nitrogenous bases are paired in the interior of the helix
- Nitrogenous bases are stacked, causing hydrophobic interactions
- There are 10 bases per turn of DNA helix
- (Don’t be confused with 3.6 amino acids every turn of a-helix in protein 2nd struc)
. - hydrophilic sugar-phosphate backbones on outside of helix
- SO DNA IS soluble in aq medium like in nucleoplasm
_______ _______ _______ _______
- bases of the 2 strands are joined tgt via complementary base pairing where:
. - Adenine pairs with Thymine via 2 H bonds
- Cytosine pairs with guanine via 3 H bonds
- 2 polynucleotides held tgt by H bonds btwn paired nitrogenous bases
_______ _______ _______ _______
- Big groove in DNA is major groove
- Small groove is minor groove
Function of DNA
- DNA is a genetic material that organisms inherit from their parents
- most DNA molecules are very long
- There are many genes on a DNA molecule
- Each gene occupies a specific region along the DNA molecule
- a gene is a unit of inheritance & stores coded instructions for the synthesis of specific molecules like RNA and proteins
. - During cell division, replication of DNA occurs
- during cell division (semi-conservative replication), 2 polynucleotide strands are separated, each strand acts as a template for the synthesis of a new complementary strand
Making transgenetic bacteria that produces insulin
- Obtain the fragment of DNA in human chromosome that contains the insulin gene
- Cut the insulin gene using a restriction enzyme to produce 2 sticky ends
- A sticky end is a single strand of DNA bases - Obtain a DNA plasmid from a bacterium cell
- Use the same restriction enzyme to cut the bacterium plasmid and produce 2 complementary sticky ends
- Use DNA ligase to join the insulin gene w/ the bacterium plasmid forming a recombinant plasmid
- Mix the recombinant plasmid & bacterium cell tgt
- Apply temporary heat shock to open up the pores of the bacterium cell membrane so the recombinant plasmid can enter
—— - Transgenetic bacteria is produced & grown in fermenters at optimum temperature, pH & w/ nutrients
- Insulin protein from transgenetic bacteria must be extracted & purified b4 use
Benefits of genetic engineering & explanations
- ## Health Low costs of producing medicines
-
Econ & environ Production of crops that produce toxins to kill pests
- No need to use pesticides that cost $$
- Less pesticides that are harm to environment are used. Like pesticides that cause euthrophication
Ethical & social implications
- Genetic engineering technology may only be accessible to wealthier people and not poorer people.
- Greater divide between the rich and poor
- - For antibiotics Antibiotic gene may be transferred to bacteria, making diseases caused by bacteria harder to treat
2 Types of nucleic acids
- Nucleotide: monomers of DNA deoxyribonucleic acid
- Nucleoside: monomers of RNA ribonucleic acid
Diff between DNA and RNA
Deoxyribonucleic acid DNA,
- Pentose sugar is deoxyribose sugar
- Deoxyribonucleic acid: it has no oxygen on carbon-2, only H atom
- So DNA more stable & less reactive than RNA
________ _______ _______ _______
RNA (Ribonucleic acid)
- Pentose sugar is ribose sugar
- On carbon-2 it has a OH group
- RNA less stable and more reactive than DNA
What is a nucleoside
- A pentose sugar
- a nitrogenous base on 1’carbon
No phosphate group on 5’carbon
- 2 components joined via condensation rxcn 1 molecules of water of water formed
Struc of nucleotide
- 1 pentose sugar
- 1nitrogenous base on 1’ carbon
- 1 or more phosphate groups on 5’ carbon
- Phosphate group forms phosphoester bond w carbon-5 of pentose sugar via condensation rxcn w removal of 1 water molecule
. - nitrogenous base forms 1 glycosidic bond with carbon-3 of pentose sugar via condensation rxcn w removal of 1 water molecule
Diff between purines and pyrimidines. List the bases
Purines:
“Pure as gold” LARGER
- Adenine + guanine
- 2 HC rings so larger than pyrimidines
.
Pyrimidines
- CUTiePy
- Uracil, cytosine, thymine
- 1ring only so smaller than purines
What is the nature of purines and pyrimidines and why?
They are bases
- lone pair of electron on Nitrogen, they accept electrons
Struc of RNA. Ribonucleic acid
- RNA is a type of nucleic acid
- RNA molecule is a single polynucleotide chain
_______ _______ _______ _______ - RNA has much less nucleotides than DNA
- Has ribose as its pentose sugar instead of deoxyribose sugar in DNA
- RNA is less stable than DNA as it is more prone to hydrolysis by intracellular enzymes
_______ _______ _______ _______ - RNA can contain the nitrogenous bases adenine, uracil, guanine, cytosine
- RNA can develop secondary struc formed by complementary base pairing within the RNA molecule
_______ _______ _______ _______ - Adenine pairs with uracil via 2 H bonds
- Guanine pair with cytosine w/ 3 H bonds
_______ _______ _______ _______
Diff types of RNA (all involved in translation) - messenger RNA
- ribosomal RNA
- transfer RNA
summary for types of RNA
- messenger RNA
- ribosomal RNA
- transfer RNA
What is semi conservation replication?
- It is where 1 parental DNA molecule is separated into 2 strands
and both are used as a template for replication - Each daughter strand assembled by synthesising a new DNA strand using parental strand as a template via complementary base pairing
.
- Each daughter DNA molecule will have 1 conserved parental strand and 1 newly synthesis strand
Struc and function of messenger RNA
- Single stranded RNA
- mRNA synthesised by transcription of DNA in the nucleus by RNA polyermerase
- mRNA transported to cytoplasm for translation by ribosomes
- mRNA used as a template to synthesise proteins
Struc & Function Ribosomal RNA
- single-stranded RNA
- Synthesised in the nucleolus
Function:
- ribosomal proteins and rRNA assemble to form the large and small ribosomal subunits in the nucleolus
- Teh 2 subunits are transported out of the nucleus to the cytoplasm where they assemble to form ribosomes
- ribosomes are the site of protein synthesis
transfer RNA struc & 3D struc function
- tRNA single stranded RNA
- triplet base sequence known as anticodon present on tRNA
- anticodon on tRBA forms H bonds with a codon via complementary base pairing
_______ _______ _______ _______ - 3’ end known as acceptor stem
- Acceptor stem is site for aa attachment
- 2D clover leaf struc on tRNA further folds into a 3D struc
- tRNA can fit into ribosome during translation
_______ _______ _______ _______
FUNCTION tRNA - With 3D struc, tRNA transfers the correct aa to the ribosome during translation**
Phosphate group struc & where is it joined?
H3PO4 without all the H
- Phos group joined to carbon-5 of pentose sugars
How are nucleotides joined tgt to form _________?
- 5’ phosphate end of an incoming nucleotide forms strong phosphodiester bonds with the 3’ OH end of a growing polynucleotide chain
- via a condensation rxcn with the removal of 1
.
____
many nucleotides join tgt via strong phosphodiester bonds from a condensation rxcn - between OH groups on 3’ carbon of the pentose sugar of 1 nucleotide & phosphate group on 5’ carbon of another nucleotide
- to a form polynucleotide
- A pyrophosphate molecules is released
Acronym to remember steps of DNA replication
BURDEn
Bubble
Unwind
RNA primers & replication
Daughter strand
End replication problem
Semi-conservative DNA replication stage 1
Stage 1: Unwinding
- DNA Helicase recognises & binds to the origin of replication along the DNA molecule
- which is a specific sequence of nucleotides that are A-T rich
- DNA helicase uses energy from ATP to unwind and
unzip a portion of the DNA double helix - As helicase moves along the double helix just in front of the
DNA polymerase, the two parental DNA strands are separated by breaking hydrogen bonds between nitrogenous bases.
_________ _______ _______ _______ - As the two DNA strands separate, a replication bubble is formed with two replication forks, a Y-shaped region at the two ends of the bubble where the parental molecule is being unzipped.
- DNA replication proceeds in both directions from each origin of replication.
_________ _______ _______ _______ - For a prokaryotic chromosome
- only a single origin of replication is present.
_________ _______ _______ _______ - For a eukaryotic chromosome
- may have multiple origins of replication as it is_ larger than prokaryotic chromosomes_.
-** Multiple replication bubbles form** and eventually** fuse** - this speeds up the copying of the very long DNA molecules.
_________ _______ _______ _______ - Each strand is bound and stabilised by single-stranded binding proteins (SSBP)
- SSBP prevent single strands from reannealing/rewinding behind the replication fork so they can be used as templates.
- SSBP protects single strand from degradation
_________ _______ _______ _______ - The unwinding of double helix causes tighter twisting in front of the replication fork resulting in a positive supercoil
DNA topoisomerase
- introduces a break in a single strand, allowing the strand to rotate around the break,
and it reseals the strand, eliminating the positive supercoil
_________ _______ _______ _______
- Each DNA parental strand acts as a template for the synthesis of daughter strand.
- BUT DNA polymerase cannot initiate the synthesis of a polynucleotide
- DNA polymerase can only add nucleotides to the end of an already existing chain in the 5’ to 3’ direction
Stage 2 Priming.
DNA replication
- Primase (a specialized RNA polymerase)
- primase binds to the single-stranded DNA template & reads it from 3’ to 5’ direction (of the strand to be synthesised)
- Primase then synthesises RNA primers in the 5’ to 3’ direction.
________ _______ _______ _______ - RNA primers are short segments of RNA of about 5 to 10 nucleotides
- RNA primers are needed for DNA polymerase to initiate elongation as they provide the 3’OH end
________ _______ _______ _______ -
Ribonucleotides are added one by one via complementary base pairing, using the parental DNA strand as a template on both sides of a replication fork.
________ _______ _______ _______ - The single-stranded binding proteins (SSBP) are displacedwhere the RNA primers are.
Stage 3 elongation
- Before the start of DNA replication free deoxyribonucleotides are synthesised in the cytoplasm and transported into the nucleoplasm via nuclear pores.
________ _______ _______ _______ - DNA polymerase adds deoxyribonucleotides to the free 3’OH end of the RNA primer as its active site is specific for the OH group on the nucleotide.
- synthests direction
________ _______ _______ _______
• DNA polymerase catalyses the synthesis of a new strand of DNA in the 5’ to 3’ direction.
- Newly synthesised strand and parental strand are joined via
complementary base pairing,
A=T via 2 H bonds and G=C via 3 H bonds.
________ _______ _______ _______
• DNA polymerase catalyses the formation of a phosphodiester bond _between the 3’OH end of the primer and 5’ phosphate group of the deoxynucleoside triphosphate (dNTP) added.
________ _______ _______ _______
• The energy for this process comes from the two phosphate groups which are removed as the nucleotide joins the growing end.
