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GENETIC CODE, Nucleotides
phosphate group
pentose sugar
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Nucleotides
- phosphate group
- pentose sugar
- nitrogenous base
Nucleic acids
- polymers
- made from many monomers (nucleotides)
- e.g. DNA and RNA
DNA nucleotide
- deoxyribose sugar
- phosphate group
- nitrogenous base; A, T, C, G
RNA nucleotide
- ribose sugar
- phosphate group
- nitrogenous base; A,U, C, G
DNA VS RNA
- DNA double stranded
- RNA single straded
DNA
- made up of 2 polynucleotide strands that lie side by side in opposite directions
- one is 5' to 3' strand other is 3' to 5' strand
- each polynucleotide strand made up of alternating deoxyribose sugar and phosphate group
- joined by phos[hodiester bonds
- 2 strands joined together by H bonds
RNA
- made up of 1 polynucleotide strand
- RNA strand is made up of alternating phosphate groups and ribose sugars joined by phosphodiester bonds forming sugar-phosphate backbone
- nitrogenous base is projected sideways
- T replaced with U
ATP
- adenine triphosphate
- type of nucleic acid
- carries energy
PURINE VS PYRIMINDINE
- purine; A, G have double ring
- pyrimidine; T, C, U have single ring
H BONDING
- A-T = 2 BONDS
- C-G = 3 BONDS
SEMI CONSERVATIVE REPLICATION
- where half the original strand in each new daughter DNA comes from parental DNA and other half is newly synthesised
GENE
- a sequence of nucleotides that form part of the DNA molecule
- the sequence of nucleotide bases (gene) determines polypeptide chain made
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TRIPLET
- a sequence of 3 bases in a gene
- each triplet codes for an amino acid
- these triplets are known as codons
GENETIC CODE FEATURES
- degenerate; same AA can be coded for by more than one base triplet
- universal; same triplet bases code for same AA in all organisms
- non-overlapping; each base triplet read once as a discrete unit so no overlap
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DNA REPLICATION
- DNA helicase breaks H bonds between complementary base pairs
- this unwinds DNA double helix
- each separated parental strands act as a template
- free nucleotides align against complementary bases
- adjacent nucleotides are joined by condensation reactions forming phosphodiester bonds and sugar phosphate backbone
- H bonds form between bases
- creating 2 identical daughter DNA
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SECOND STEPS (PROTEIN SYNTHESIS)
- transcription
- translation
TRANSCRIPTION
- DNA is transcribed and mRNA molecule made
- occurs in nucleus of cell
- DNA double helix unwinds to expose bases
- exposing gene to be transcribed
- catalysed by DNA helicase
- only 1 strand acts as a template as mRNA is single straded
- free RNA nucleotides in nucleus align against opposite complementary bases
- RNA polymerase joins adjacent nucleotides by condensation reactions
- creating new polymer chain
- when RNA reaches stop condon, mRNA (PK) or pre-mRNA (EK) detatches
- mRNA leaves nucleus via pore
TRANSLATION
- mRNA is translated and an amino acid sequence is made
- once modifications made mRNA leaves nucleus and attaches to a ribosome at start codon
- tRNA molecules flowing in the cytoplasm have a triplet of unpaired bases at one end (anti-codon) and a region where a specific amino acid can attach
- triplet bases on each tRNA molecule pairs with complementary bases (codon) on mRNA
- 2 tRNA molecules fit onto the ribosome at once and bring the AA they are carrying side by side
- AA are joined by peptide bonds
- process continues till stop codon reached
- releasing polypeptide chain
POST TRANSCRIPTIONAL MODIFICATION
- EKC have introns and extrons
- introns are non-coding base sequences
- exons are coding sequences that will be translated into AA forming the polypeptide chain
- pre-mRNA has to be modified before it is ready to leave the nucleus
- introns are spliced out using a splicesome, this breaks the phosphodiester bonds leaving behind just the exons
- PK DNA doesn't have introns so mRNA is produced directly from DNA
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TYPES OF MUTATION
- insertion -> causes knock off effect
- deletion -> nucleotide is delteded, causes knock off effect
- substitution -> one DNA base swapped for another, no knock off effect: 3 types
SUBSTITUTION MUTATION
- silent - mutation doesn't change AA being coded for as genetic code degenerate
- missense - mutation alters single AA
- nonsense - mutation creates premature stop-codon
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CHROMOSOME STRUCTURE
- made up of 1 long condensed DNA associated with proteins
- histonses organise and condense DNA tightly so can fit in nucleus
WHEN DNA REPLICATES:
- 2 identical strands of DNA (chromatids) formed
- joined together at centre by centromere
- they are known as sister chromatids
MITOSIS
- the process of nuclear division by which 2 genetically identical daughter nuclei produced
USES:
- release old/dead cells
- asexual reproduction
- repair of tissues
- growth of multicellular organsm
CELL CYCLE
- form a cell, it grows then divides to form 2 identical daughter nuclei
- made up of 3 phases; interphase, mitosis, cell division (cytokinesis)
INTERPHASE
- cell grows and prepared to divide
- chromosomes and some organelles replicated
- chromosomes begin to condense
- G1 + S + G2 = INTERPHASE
G1
- signal received telling cell to divide again
- prepares for growth by and DNA synthesis by making proteins and enzymes
- 46 chromosome, 46 chromatids
S
- DNA in nucleus replicates resulting in each chromosome consisting of 2 chromatids
- 46 chromosomes 96 chromatids
G2
- DNA is checked for errors and repaides
TELOMERE
- they ensure very ends of DNA molecule are included in DNA replication
- as copying enzyme unable to run to very end
- so important genes may be lost during each replicatipn
- made of non-coding DNA
- most cells have telemorase that adds bases to each end to avoid loosing genes
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Stem cell
- cells that have the ability to divide an unlimited number of times by mitosis
- they have the potential to remain as a stem cell or differentiate into a specilaised cell e.g. blood cell
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Uses of stem cells:
- growth
- cell replacement
- tissue repair
POTENCY:
- the ability fo a stem cell to differentiate into more specialised cell types; 3 types
- totipotency - ability to differentiate into any cell type in an embryo and extra embryonic cells
- pluripotency - ability to differentiate in any cell type in an embryo but not extra embryonic cells
- multipotency - adult stem cells have the ability to differentiate into few types of cells
PROPHASE
- chromatin condenses
- chromosomes become shorter and thicker
- visible as 2 sister chromatids
- centrosomes move to opp poles
- nucleuolus and nuclear envelope break down
METAPHASE
- centrosomes reach app poles
- spindle fibres begin to extend from centrosome
- chromosomes align at centre of cell
- spindle fibres reach centrometre
ANAPHASE
- centromere divides separating sister chromaids
- spindle fibres shorter
- this pulls chromatids to opposite poles
TELOPHASE
- chromosomes reach opp poles
- being to decondense, return to long thin chromatid
- nuclear envelope reforms and nucleolus
- spindle fibres break down
CYTOKINESIS
- division of cell cytoplasm
- in animals membrane drawn together by microfilament forming clevage furrow
- in plants, vesicles transported to equate and fuse together to form cell wall
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Cholera
Malaria
HIV
- human immunodeficiency virus
- virus
TB
- mycobacterium tuberculosis
- bacterium
TRANSMISSION CHOLERA
- disease is water borne
- transmitted by drinking/eating/bathing in contaiminated water
MALARIA
- transmitted by mosquito vector (female anopheles)/needles
- they feed on an individual infected with plasmodium and it takes in some of the bacterium
- when feeding on next human some of the bacteria is transmitted to their blood
TB
- air borne droplets
- transmitted when uninfected inhale. these droplets
HIV
- spread by exchange of bodily fluids; sex, blood donation, needles
PREVENTION and TRATMENT
- cholera - sewage treatment, clean piped water, vacicnation
- oral rehydration, antibiotics
- maleria - spray insecticides, oil over water body, drain marsh, take prophylactic drugs, sleep under net
- TB - BCG vaccine, pasterise milk, testing cattle
- HIV - blood donations screened, HIV positive mother/babdy treat with drugs, condom, not sharing needles
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Antibotics function
- kill/stop growth of bacteria but don't harm cells of infected organisms
HOW THEY WORK:
- bacterial cell walls made from peptidoglycan
- these walls are held by cross links between them
- when bacteria is growing it secretes enzymes that create small holes in the cell wall
- these holes allow them to stretch and join with new cross links
- penecillin stops cross links forming by inhibiting enzymes that catalyse their production
- so holes keep getting created making them weaker
- as bacteria live in watery environment they take water in by osmosis the weakened walls burst
THEY DONT WORK ON VIRUSES AS THEY DONT HAVE CELL WALLS
Antibiotic resistance
2 ways they can be spread
- vertical transmission, bacteria reproduce by binary fission (when DNA of bacteria replicated and bacterial cell divides into 2). If one mutant gene present giving antibiotic resistance decentadawts have this too
- horizontal, plasmids often contain antibiotic resistance genes. Plasmids are frequently transferred between bacteria during congugation (where bacteria exchange DNA) so gene could be passed on
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Structures:
- arteries = carry blood away from heart, lots of muscular walls, narrow lumen
- arterioles = small arteries that branch from larger ones and attach to capillaries
- capillaries = tiny blood vessels that connect to arterioles and venules
- venues = small veins which join capillaries to larger veins
- veins = carry blood into heart, thin walls , less muscles, values
ARTERIES
- thick walls --> withstand high pressure
- elastic tissue - stretch/recoil maintain pressure
- narrow lumen - ensure blood remain at high pressure
- smooth muscle regulate blood flow
Cells in blood
- RBC - lack nucleus
- monocyte - largest WBC, nucleus kidney bean shape
- neutrophils, multi lobed nucleus
- lymphocytes, large nuclei
Formation of tissue fluid
- high hydrostatic pressure of blood
- leakage of plasma through gaps in capillary
- e.g. glucose
Transport of oxygen
- oxygen is bound to protein haemoglobin in RBC
- each mol of heamoglobin contains 4 harm groups which can bind to 1 oxygen
- when binds forms oxyhaemoglobin
- after first molecule binds conformational change occurs making it easier for successive oxygen molecules to bind
CHLORIDE SHIFT
- the movement of chloride ions into RBC that occurs when HCO3- ions made by transport protein
- to prevent electrical imbalance otherwise RBC become positively charged due to H+ ions from dissociation of carbonic acid
How hydrogen carbonate ions made:
- CO2 diffuse into RBC
- enzyme carbonic anhydrase catalyses conbination of CO2 and H2O to make carbonic acid
- this dissociates into carbonate ions and H+ ions
BOHR SHIFT
- occurs at high partial pressure of CO2, causes haemoglobin to release oxygen to respiring tissues
Transport of CO2 from respiring cells:
- CO2 diffuses down conc gradient from respiring cells to plasma
- some CO2 diffuses into RBC to combine with haemoglobin forming carboaminohaemaglobin
- some CO2 coming with water to form carbonic acid
- this dissociates to form HCO3- and diffuses out of RBC into plasma
Ways CO2 can be transported around body?
- in blood plasma in form of HCO3- ions
- dissolving directly in plasma
- binding to haemoglobin carboaminohaemoglobin