TOPIC 4

DNA, GENES AND CHROMOSOMES

-BOTH DNA & RNA CARRY INFO

• DNA HOLDS GENETIC INFO WHEREAS RNA TRANSFERS IT FROM DNA TO RIBOSOMES MADE OF rRNA & PROTEINS
• BOTH DEOXYRIBOSE NUCLEIC ACIDS & RIBONUCLEIC ACID ARE POLYMERS OF NUCLEOTIDES
• NUCLEOTIDES HAVE PENTOSE SUGAR, NITROGENOUS BASE & PHOSPHATE GROUP

-DNA ORGANIC BASES- ADENINE & THYMINE, CYTOSINE & GUANINE

-RNA ORGANIC BASES-  ADENINE & URACIL, CYTOSINE & GUANINE

-(A) & (G) = PURINE BASES (DOUBLE RING STRUCTURE)

-(T), (C) & (U) = PYRIMIDINE BASES (SINGLE RING STRUCTURE)

-NUCLEOTIDES JOINED BY PHOSPHODIESTER BONDS FORMED IN CONDENSATION REACTIONS

-DNA MOLECULE= DOUBLE HELIX COMPOSED OF 2 POLYNUCLEOTIDES JOINED BY H BONDS (COMP) 

GENETIC CODE

-ORDER OF BASES ON DNA (CONSISTS OF TRIPLET BASES)

-CODON= TRIPLET BASE CODING FOR PARTICULAR AMINO ACID

-AMINO ACIDS THEN JOINED BY PEPTIDE BONDS & FORM POLYPEPTIDE CHAIN

-GENE= SEQUENCE OF BASES ON DNA MOLECULE CODING FOR SEQUENCE OF AMINO ACID IN POLYPEPTIDE CHAIN

-LOCUS= LOCATION OF GENE

-INTORN= NON-CODING SECTION OF DNA

-EXON= CODING SECTION OF DNA

-4 NUCLEOTIDES BASES CODE FOR 20 AMINO ACIDS- 64 POSSIBLE TRIPLETS (1 OR MORE COMBOS)

GENETIC CODE

-FEAUTES OF GENETIC CODE

• NON-OVERLAPPING SECTION (EACH TRIPLET READ ONCE & DON'T SHARE BASES)
• GENES SEPERATED BY NON-CODING REPEATS OF BASES
• DEGENERATE- MORE THAN 1 TRIPLET CODES FOR SAME AMINO ACID- REDUCES NUMBER OF MUTATIONS (MISTAKES IN BASE SEQUENCES) LIKE BASE DELETION, INSERTION OR SUBSTITUTION
• CHANGE IN BASE SEQUENCE OF DNA ALTERS AMINO ACID SEQUENCE & PROTEIN & HAS EFFECTS
• SOME MUTATIONS HARMFUL (E.G., PRODUCTION OF STICKY MUCUS LEADING TO CYSTIC FIBROSIS)
• CONTAINS STOP & START CODONS

-EUKARYOTIC CELLS

• DNA FOUND IN NUCLEUS & LONG & LINEAR
• ASSOCIATED WITH HISTONES (PROTEINS) TO FORM CHROMOSOMES (VISIBLE AT START OF CELL DIVISION & IS RESULT OF DNA BEING TIGHTLY COILED AROUND HISTONES)
• MITOCHONDRIA & CHLOROPLASTS CONTAIN DNA (PROKARYTOIC OPPOSITE)

GENETIC CODE

-HUMANS HAVE 46 CHROMOSOMES IN EVERY CELL IN BODY ARRANGED INTO HOMOLOGOUS PAIRS (CONSIST OF 2 CHROMOSOMES THAT CARRY SAME GENES)

-NOT IDENTICAL AS CAN CARRY DIFFERENT ALLELES OF SAME GENE

-23RD CHROMOSOME DETERMINES SEX OF INDIVIDUAL

-FEMALE= X X

-MALE= X Y

-ALLELE= ALTERNATIVE FORM OF SAME GENE, EITH EVERY GENE EXISTING IN 2 OR MORE FORMS

-INHERIT 2 ALLELES OF EVERY GENE FROM PARENT

-CHROMOSOME= STRING OF DNA WRAPPED AROUND ASSOCIATED PROTEINS THAT GIVE CONNECTED NUCLEIC ACIDS BASES A STRUCTURE

DNA AND PROTEIN SYNTHESIS

-2 STAGES OF PROTEIN SYNTHESIS

• TRANSCRIPTION OCCURS IN NUCLEUS & INVOLVES DNA & mRNA
• TRANSLATION INVOLVES mRNA, rRNA & RIBOSOMES

-STRUCTURE OF mRNA (MESSENGER RNA)

• LONG SINGLE STRAND CREATED DURING TRANSCRIPTION IN WHICH BASE SEQUENCE IS COMPLEMENTARY TO DNA
• EACH CODON MATCHES TRIPLET ON DNA & tRNA

-STRUCTURE OF tRNA (TRANSFER RNA)

• SMALL MOLECULE MADE UP OF AROUND 80 NUCLEOTIDES- SINGLE STRAND FOLDED INTO CLOVER LEAF SHAPE IN WHICH ONE END EXTENDS FROM OTHERS (AMINO ACID ATTATCHES)
• AT OPPOSITE END IS AN ANTI-CODON, SPECIFIC TO AMINO ACID tRNA ATTACHES TO

DNA AND PROTEIN SYNTHESIS

-TRANSCRIPTION

• HYDORGEN BONDS BETWEEN COMPLEMENTARY BASES BREAK DUE TO ACTION OF ENZYME & DNA UNCOILS, SEPERATING 2 STRANDS, EXPOSING ORGANIC BASES- 1 OF DNA STRANDS USED AS TEMPLATE TO MAKE mRNA (ANTISENSE STRAND)
• FREE NUCLEOTIDES LINE UP BY COMPLEMENTARY BASE PAIRING &  ADJACENT NUCLEOTIDES JOINED BY PHOSPHODIESTER BONDS, FORMING MOLECULE OF mRNA
• ENZYME RNA POLYMERASE CATALYSES FORMATION OF PHOSPHODIESTER BONDS- WHEN STOP CODON REACHED, IT CEASES- AS RNA POLYMERASE MOVES AWAY, DNA REJOINS WITH ONLY 12 BASES EXPOSED AT A TIME TO REDUCE CHANCE OF DAMAGE TO DNA
• IN EUKARYOTIC CELLS, PRE-mRNA THEN SPLICED TO REMOVE INTRONS, LEAVING JUST STRAND OF EXONS 
• mRNA THEN MOVES OUT OF NUCLEUS THROUGH PORE & ATTATCHES TO RIBOSOME IN CYTOPLASM (SITE OF TRANSLATION) 

-SPLICING=REMOVAL OF NON-CODING RNA PARTS (CAN'T CODE FOR AMINO ACIDS)

DNA AND PROTEIN SYNTHESIS

-TRANSLATION

• mRNA ATTATCHES TO RIBOSOME & tRNA COLLECTS AMINO ACIDS FROM CYTOPLASM & CARRIES THEM TO RIBOSOMES -tRNA= SINGLE STRANDED MOLECULE WITH BINDING SITE AT ONE END (CAN CARRY ONLY 1 AMINO ACID) & TRIPLET BASE (ANTI-CODON) ON OTHER END
• tRNA  ATTACHES ITSELF TO mRNA BY COMPLEMENTRAY BASE PAIRING- 2 MOLECULES ATTACH TO mRNA AT A TIME
• AMINO ACIDS ATTATCHED TO 2 tRNA MOLECULES JOIN BY PEPTIDE BONDS & THEN tRNA MOLECULES DETACH THEMSELVES FROM AMINO ACIDS, LEAVING THEM
• PROCESS REPEATED, LEADING TO FORMATION OF POLYPEPTIDE CHAIN UNTIL STOP CODON REACHED ON mRNA & ENDS PROTEIN SYNTHESIS PROCESS

-RIBOSOMES CAN JOIN UP TO 15 AMINO ACIDS PER SECOND UNTIL STOP CODON REACHED

-UP TO 50 RIBOSOMES CAN MOVE ALONG SAME mRNA STRAND (PROTEINS ASSEMBLED SIMULTANEOUSLY)

-ANTICODON= TRIPLET BASES PRENSENT IN tRNA (COMP TO CODONS IN mRNA)

GENETIC MUTATION

-CHANGES IN DNA CAN ARISE SPONTANEOUSLY DURING REPLICATION

-MUTATION= ANY CHANGE IN BASE SEQUENCE OR QUANTITY OF DNA

-CHANGE IN BASE SEQUENCE OF GENES CAN CHANGE AMINO ACIDS SEQUENCE (CAN RESULT IN HARMFUL MUTATION)

-MAY NOT CHANGE AMINO ACID SEQUENCE BECAUSE CODE IS DEGENERATE

-2 TYPES OF MUTATION

• SUBSTITUTION: WHEN 1 NUCLEOTIDE IS REPLACED BY ANOTHER- EFFECT OF CHANGE IN AMINO ACID DEPENDS ON ROLE OF ORIGINAL AMINO ACIDS IN OVERALL SHAPE & FUCTION OF PROTEIN (MAY NOT ALWAYS BE HARMFUL AS SUBSTITUED NUCLEOTIDE MAY CODE IN THAT TRIPLE FOR SAME AMINO ACID)
• DELETION: WHEN NUCLEOTIDE IN DNA SEQUENCE IS LOST- LOSS OF SINGULAR NUCLEOTIDE CAN HAVE SIGNIFICANT IMPACT AS IT LEADS TO FRAME SHIFT (RESULTING IN COMPLETELY DIFFERENT AMINO ACIDS BEING CODED FOR)

GENETIC MUTATION

-2 FORMS APPEARING IN CHROMOSOMES

• POLYPLOIDY: CHANGES CAN OCCUR IN WHOLE SET OF CHROMOSOMES SO THAT INDIVIDUAL HAS 3 OR MORE SETS OF CHROMOSOMES INSTEAD OF 2 (COMMON IN PLANTS)
• NON-DISJUNCTION: OCCURS WHEN CHROMOSOMES FAIL TO SEPERATE CORRECTLY IN MEIOSIS- RESULT= GAMETES & ZYGOTES FORMED WILL HAVE 1 MORE OR 1 LESS CHROMOSOME THAN THEY SHOULD (E.G., DOWN'S SYNDROME, INDIVIDUALS HAVE EXTRA CHROMOSOME 21)

MEIOSIS AND GENETIC VARIATION

-MEIOSIS= FORM OF CELL DIVISION THAT GIVES RISE TO 4 DAUGHTER CELLS THAT ARE GENETICALLY DIFFERENT & HAVE 1/2 NUMBER OF CHROMOMES FOUND IN PARENT CELL

-MAIN ROLE OF MEIOSIS- PRODUCTION OF HAPLOID GAMETES (AS CELLS PRODUCED HAVE 1/2 NUMBER OF CHROMOSOMES) -NECESSARY TO MAINTAIN STABLE NUMBER OF CHROMOSOMES

-GENETIC VARIATION ACHIEVED THROUGH

• INDEPENDENT ASSORTMENT OF CHROMOSOOMES: (VARIOUS COMBINATIONS OF CHROMOSOME ASSORTMENT) DURING MEIOSIS 1, HOMOLOGOUS CHROMOSOMES LINE UP IN PAIRS, ARRANGEMENT IS RANDOM (DIVISION INTO DAUGTER CELLS ALSO RANDOM)
• CROSSING OVER OF CHROMATIDS: (WHEN PAIRS OF CHROMOSOMES LINE UP THEY CAN EXCHANGE SOME GENETIC MATERIAL) OCCURS WHEN 1 CHROMOSOME MAY SWAP PLACES WITH SAME PART OF ITS HOMOLOGOUS PAIR LEADING TO DIFFERENT COMBINATION OF ALLELES ON GENES

MEIOSIS AND GENETIC VARIATION

-STAGES OF MEIOSIS

• MEIOSIS 1: HOMOLOGOUS CHROMOSOMES PAIR UP WHERBY CROSSING OVER AT CHIASMATA MAY TAKE PLACE- CELL THEN DIVIDES WHEREBY EACH DAUGHTER CELL CONTAINS 1 CHROMOSOME FROM EACH HOMOLOGOUS PAIR
• MEIOSIS 2:CHROMATIDS OF EACH CHROMOSOME SEPERATED PRODUCING 4 HAPLOID DAUGHTER CELLS

GENETIC DIVERSITY AND ADAPTATIONS

-GENETIC DIVERISTY= TOTAL NUMBER OF DIFFERENT ALLELES IN POPULATION

-POPULATION= GROUP OF INDIVIDUALS OF SAME SPECIES THAT LIVE IN SAME PLACE AND CAN BREED WITH EACH OTHER

-GREATER NUMBER OF ALLELES IN POPULATION= GREATER GENETIC DIVERSITY= GREATER CHANCE THAT POPULATION WOULD SURVIVE CHANGE IN THEIR HABITAT

-NICHE OF SPECIES= ROLE WITHIN ENVIRONMENT (SAME NICHE- COMPETE WITH EACH OTHER)

-NATURAL SELECTION= PROCESS IN WHICH FITTER INDIVIDUALS WHO ARE BETTER ADAPTED TO ENVIRONMENT SURVIVE & PASS ON ADVANTAGEOUS GENES TO FUTURE GENERATIONS

-EVOLUTION= PROCESS BY WHICH FREQUENCY OF ALLELES IN GENE POOL CHANGES OVER TIME AS RESULT OF NATURAL SELECTION

GENETIC DIVERSITY AND ADAPTIONS

-EVOLUTION VIA NATURAL SELECION

• VARIETY OF DIFFERENT PHENOTYPES WITHIN POPULATION
• ENVIRONMENTAL CHANGE OCCURS & AS RESULT OF THAT, SELECTION PRESSURE CHANGES SOME INDIVIDUALS POSESS ADVANTAGEOUS ALLELES WHICH GIVE THEM SELECTIVE ADVANTAGE & ALLOW THEM TO SURVIVE & REPRODUCE
• ADVANTAGEOUS ALLELES PASSED ON TO THEIR OFFSPRING
• OVER TIME, FREQUENCY OF ALLELES IN POPULATIONS CHANGE & LEAD TO EVOLUTION

-SELECTION= PROCESS BY WHICH INDIVIDUALS THAT ARE BETTER ADAPTED TO THEIR ENVIRONMENT ARE MORE LIKELY TO SURVIVE & BREED (MEANS THEY CAN PASS ON ADVANTAGEOUS ALLELES)

- EVERY LIVING ORGANISM SUBJECT TO SELETION DETERMINED BY CONDITIONS IN WHICH THEY ARE LIVING

GENETIC DIVERSITY AND ADAPTIONS

-2 TYPES OF SELECTION

-DIRECTIONAL SELECTION

• OCCURS WHEN ENVIRONMENTAL CONDITIONS CHANGE & PHENOTYPES BEST SUITED TO NEW CONDITIONS ARE MORE LIKELY TO SURVIVE (RESULT= INDIVIDUALS BREED & PRODUCE)
• OVERTIME, MEAN OF POPULATION WILL MOVE IN DIRECTION OF THEM
• E.G., BACTERIA BEING RESISTENT TO ANTIBIOTICS- SINGLE BACTERIA WILL HAVE HAD MUATION THAT MEANT ITS WASN'T KILLED BY PENICILIN AS IT COULD PRODUCE ENZYME PENICILLINASE (RESULT= ABLE TO GROW & POPULATE & FREQUENCY OF ALLELE THAT ENABLED PENICILLINASE PRODUCTION INCREASED IN POPULATION= POPULATION MOVED TO HAVE GREATER PENICILIN RESISTANCE)

-STABILISING SELECTION

• PHENEOTYPES WITH SUCCESSFUL CHARACTERISTICS PRESERVED & THOSE OF GREATER DIVERSITY REDUCED (DOESN'T OCCUR DUE TO CHANGES IN ENVIRONMENT- IF ENVIRONMENT STAYS SAME THE INDIVIDUAL CLOSEST TO MEAN ARE FAVOURED BECAUSE THEY HAVE ADVANTAEGOUS ALLELES)
• E.G., BABIES BORN AROUND 3KG MORE LIKELY TO SURVIVE

GENETIC DIVERSITY AND ADAPTATIONS

-SPECIES WITH SAME NICHE COMPETE & BETTER ADAPTED SPECIES SURVIVES

-WAYS ORGANISMS ARE ADAPTED TO ENVIRONMENT

• ANATOMICAL  ADAPTATIONS (PHYSICAL)- EITHER EXTERNAL OR INTERNAL- E.G., LENGTH OF LOOP OF HENLÉ, HELPS DESSERT MAMMALS TO PRODUCE CONCENTRATED URINE & MINIMISE WATER LOSS
• BEHAVIORAL ADAPTATIONS (CHANGES)- IMPROVE ORGANISM'S CHANCE OF SURVIVAL- E.G., MATING CALL
• PHYSIOLOGICAL ADAPTATIONS (PROCESS INSIDE BODY)- INCREASE CHANCE OF SURVIVAL- E.G., REGULATION OF BLOOD FLOW THROUGH SKIN

SPECIES AND TAXONOMY

-SPECIES CAPABLE OF PRODUCING OFFSPRING

-BINOMIAL NAMING SYSTEM- GENERIC NAME= GENUS TO WHICH ORGANISM BELONGS & SPECIFIC NAME= SPECIES TO WHICH ORGANISM BELONGS (UNDERLINED & FIRST LETTER (G) CAPITALISED)

-COURTSHIP BEHAVIOUR

-MEMBERS OF SAME SPECIES SHARE SIMILAR PHYSICAL, BIOCHEMICAL & BEHAVIOURAL CHARACTERISTICS

• RECOGNISE MEMBERS OF OWN SPECIES
• SYNCHRONISE MATING
• FORM PAIR BOND
• BECOME ABLE TO BREED

SPECIES AND TAXOMONY

-CLASSIFICATION= PROCESS OF NAMING & ORGANISING ORGANISMS INTO GROUPS BASED ON THEIR CHARACTERISTICS

-3 DOMAINS= BACTERIA, ARCHAE & EUKARYOTA

-5 KINGDOMS= ANIMALS, PLANTS, FUNGI, PROKARYOTES & PROTOCTISTS

-DOMAIN - KINGDOM - PHYLUM - CLASS - ORDER - FAMILY - GENUS - SPECIES

-MOLECULAR PHYLOGENY= ANALYSIS OF MOLECULAR DIFFERENCES IN DIFFERENT ORGANISMS TO DETERMINE EXTENT OF THEIR EVOLUTIONARY RELATEDNESS

-DATA EVALUATION

• FINDINGS PUBLISHED IN SCIENTIFIC JOURNALS & PRESENTED IN SCIENTIFIC CONFERENCES
• PEER REVIEW
• COLLECT EVIDENCE TO EITHER SUPPORT OR REJECT SUGGESTION

BIODIVERSITY WITHIN A COMMUNITY

-BIODIVERSITY= VARIETY OF LIVING ORGANISMS

-VARIETY OF LIFE THREATENED BY HUMAN ACTIVITIES (E.G., DEFORESTATION)

-MEASURE BIODIVERSITY

• SPECIES DIVERSITY= NUMBER OF DIFFERENT SPECIES & NUMBER OF DIFFERNET INDIVIDUALS IN COMMUNITY (MEASURED BY COUNTING NUMBER OF SPECIES PRESENT VIA METHODS SUCH AS RANDOM SAMPLING)
• GENETIC DIVERSITY= GENETIC VARIATION FOUND IN PARTICULAR SPECIES (NUMBER OF ALLELES IN GENE POOL)
• ECOSYSTEM DIVERSITY= RANGE OF DIFFERENT HABITATS

-INDEX OF DIVERSITY

-D= DIVERSITY INDEX, N= TOATL NUMBER OF ORGANISMS, n= TOTAL NUMBER OF ORGANISMS IN EACH SPECIES, Σ= SUM OF        D= N(N-1) / Σn(n-1)

BIODIVERSITY WITHIN A COMMUNITY

-IMPACTS OF AGRICULTURE

-AGRICULTURAL ECOSYSTEMS RECUDE BIODIVERISTY & NUMBER OF SPECIES PRESENT BECAUSE HUMANS SELECT FOR PARTICULAR CHARACTERISTICS

-REDUCES NUMBER OF ALLELES & GENETIC DIVERSITY OF POPULATIONS

-FARMLAND TYPICALLY USED FOR SINGLE SPECIES WHICH MEANS FEWER INDIVIDUALS OF OTHER SPECIES CAN SURVIVE THERE

-MAINTAIN BIODIVERSITY

• USE HEDGEROWS INSTEAD OF FENCES
• INTERCROPPING= GROWING DIFFERENT CROPS IN SAME AREA
• REDUCING USE OF HERBICIDES & PESTICIDES
• PRESERVING WETLANDS INSTEAD OF DRAINING THEM FOR FARMING USE

COMPARING GENETIC DIVERSTIY

-GENETIC DIVERSITY WITHIN OR BETWEEN SPECIESCAN BE DETERMINED BY COMPARING FREQUENCY OF MEASUREABLE/ OBSERVABLE CHARACTERISTICS, BASE SEQUENCE OF DNA, BASE SEQUENCE OF mRNA & AMINO ACID SEQUENCE OF PROTEINS ENCODED BY DNA & mRNA

-LIMITATIONS OF USING OBSERVABLE CHARACTERISTICS

• CHARACTERISTICS COULD BE CODED FOR BY MORE THAN 1 GENE
• SAME CHARACTERISTIC COULD HAVE ARISEN SEPERATELY
• CHARACTERISTICS COULD BE INFLUENCED BY ENVIRONMENT AND NOT GENES

-SCIENTISTS NOW USE GENE TECHNOLOGY TO READ BASE SEQUENCES OF ORGANISMS

-GENETIC DIVERSITY CAN BE MEASURED BY SAMPLING DNA OR mRNA FROM DIFFERENT INDIVIDUALS

-AMINO ACIDS SEQUENCE CAN ALSO BE STUDIED AS IT CAN BE TAKEN BACK TO mRNA SEQUENCE & THEN DNA SEQUENCE

COMPARING GENETIC DIVERSITY

-INTERSPECIFIC VARIATION=DIFFERNCES BETWEEN SPECIES

-INTRASPECIFICVARIATION= DIFFERENCES BETWEEN INDIVIDUALS OF SAME SPECIES

-MEASURING CHARACTERISTICS IN SPECIES (SCIENTISTS CAN'T MEASURE EACH INDIVIDUAL)- USE SAMPLING

-SAMPLING= RANDOM SELECTION OF INDIVIDUALS TO MEASURE

-MAY NOT BE REPRESENTATIVE OF POPULATION DUE TO CHANCE OR SAMPLING BIAS

-ELIMINATE SAMPLING BIAS- USE QUADRAT (SQUARE FRAME TO DEFINE SIZE) OR TRANSECT (LINE ACROSS HABITAT) BY PLAING ON RANDOMLY GENERATED COORDINATES IN SAMPLE AREA

-INCREASE RELIABILITY- USE LARGER SAMPLE SIZE