THE GENETIC CODE AND THE CELL CYCLE Flashcards
3 aspects of nucleotide structure
- pentose sugar
- phosphate group
- organic base
bond between sugar and phosphate in polynucleotide
phosphodiester
pentose sugar type on RNA
ribose
pentose sugar type on DNA
deoxyribose
3 RNA types
- transfer genetic material from DNA to ribosomes
- ribosomes made up of another RNA type and proteins
- involved in protein synthesis
bonds between complimentary bases in DNA
hydrogen
number of bonds between C and G
3
DNA functional adaptations (6)
- double stranded - replication can occur semiconservativly
- H bonds between strands allow separation during protein synthesis and DNA replication
- large = lots of genetic material stored
- base pairs protected within helix by backbone
- base sequence allows information to be stored
- long and coiled tightly into chromosomes = space efficient
number of bonds between A and T
2
chromosomes in eukaryotes vs prokaryotes
eu = wound tightly around histone proteins to make chromosomes pro = coiled tightly NOT associated with histones
shape of DNA in eukaryotes vs prokaryotes
eu = long and linear pro = short and circular
semiconservative replication
one strand from old in each of the new strands
DNA helicase function
at replication fork - splits double helix by breaking H bonds between bases
DNA polymerase function
forms phosphodiester bonds in the backbone on the LEADING STRAND via condensation reaction
DNA ligase function
joins Okazaki fragments on LAGGING STRAND via condensation reaction to make phosphodiester bonds and form backbone
replication on leading strand
continual, 5 to 3 direction
replication on lagging strand
in Okazaki fragments, joined by DNA ligase
prophase
- chromosomes shorten and thicken (visible under microscope)
- nuclear membrane disappears
metaphase
- centrioles migrate to the poles of the cell
- spindle fibres pull chromosomes to align at the equator of the call
anaphase
- spindle fibres pull chromatids to poles of the cell
centromeres split in 2
telophase
- cytokinesis - cytoplasm and membrane split into 2, forming 2 discreet daughter cells
interphase
- chromosomes replicate - now made up of 2 chromatids joined by a centromere
purine bases
A T U
pyramidine bases
C G
tRNA features 4
- 80 nucleotides roughly
- single strand that folds up into a clover shape
- different types each binding to different amino acid
- has anticodon at end (3 bases)
reaction type forming a dinucleotide
condensation reaction
organic bases in RNA
C, G, A, U
DNA function
passing genetic information between cells
stages of DNA replication (4)
1) DNA helices breaks h-bonds between complimentary base pairs, unwinding the molecule into 2 separate strands, exposing template strands
2) exposed polynucleotide strand then acts as a template for complimentary free nucleotide bases to bind to by base pairing
3) nucleotides are joined by DNA polymerase in a series of condensation reactions, forming phosphodiester bonds
4) creating 2 daughter strands, each containing one original strand = semiconservative
requirements of semiconservative replication (4)
1) 4 types of free nucleotides, each with their bases must be present
2) both strands of dna act as a template for the attachment of nucleotides
3) enzyme dna polymerase
4) source of chemical energy to drive process
differences between eukaryotic and prokaryotic DNA (2)
- eukaryotic wound around histone proteins to make chromosomes vs. prokaryotic is wound into chromosomes but not associated with histones
- eukaryotic is long and linear vs prokaryotic is short and circular
codon
3 nucleotides which code for an amino acid
degenerate
some amino acids are coded for by more then 1 codon
regions of non coding DNA
introns
charge carried by nucleic acid molecules
negative
purines
types of organic bases made up of 2 rings of carbon and nitrogen atoms
pyrimidines
types of organic bases made up of a single ring of carbon and nitrogen atoms
product of transcription
a mRNA copy of part of DNA
translation
process by which amino acids are assembled using code carried by mRNA
types of mutation (6)
- substitution
- deletion
- addition
- translocation
- inversion of bases
- duplication
interspecific variation
one species differs from another
intraspecific variation
members of the same species differ from eachother
first name in binomial system
genus
second name in binomial system
species
how do courtship behaviours increase chance of successful mating? (4)
- recognise members of their own species, insuring mating is only within the species
- identify mate which is capable of breeding
- form a pair bond - leading to successful breeding and raising offspring
- synchronised mating - so takes place at max probability of conception
2 main forms of classification
- artificial
- phylogenetic
artificial classification
divides organisms according to differences that are useful at the time (eg. no of legs, colour, size) - same function but not the same evolutionary oragin
phylogenetic classification
- based on evolutionary relationships between organisms and their ancestors
- classifies into groups using shared characteristics/ features derived from ancestors
- arranges groups into a hierarchy In which groups are contained within larger, composite groups with no overlap
[- looks at features, behaviours and observations]
characteristics which artificial classification is based on
analogous - same function but not same evolutionary origins
characteristics which phylogenetic classification is based on
homologous - similar evolutionary origins regardless of function
taxon
group within phylogenetic classification
3 domains
Archea, bacteria and eukarya
bacteria
group of single celled prokaryotes
features of bacteria (5)
- absence of membrane bound organelles
- unicellular
- ribosomes are smaller (70s)
- cell walls are present and made of murein
- single loop of naked DNA made up of nucleic acid - no histones
Archea
group of single celled prokaryotes
how do archea differ from bacteria (4)
- have genes and undergo protein synthesis
- membranes contain fatty acid chains attached to glycerol by ester linkages
- no murein in cell walls
- more complex form of RNA polymerase
eukarya
group of organisms made up of 1+ eukaryotic cells
features of eukarya (4)
- cells contain membrane bound organelles
- have membranes containing fatty acid attached to glycerol by ester linkages
- not all posses a cell wall, but those which do contain no murein
- ribosomes are larger (80s)
4 kingdoms of eukarya
- protoctista
- fungi
- plantae
- Animalia
classification rank
domain>kingdom>phylum>class>order>family>genus>species
why may it be difficult to separate individuals into different species (5)
- species aren’t fixed and constantly evolve - some may develop into new species
- considerable variation within species
- many are extinct and have left no fossil record
- some species rarely, if ever reproduce sexually
- some individuals in a species may be physically separated and never meet and interbreed
species
individuals which can breed to produce live, fertile offspring
4 methods of investigating biodiversity
- observable characteristics
- comparing dna base sequences
- comparing mRNA base sequences
- comparing amino acid sequences in proteins
genome
the complete set of genes in a cell
proteome
the full range of proteins a cell can produce
RNA structure
single polynucleotide strand containing uracil instead of thymine
- pentose sugar - ribose
- phosphate group
what stage of protein synthesis is mRNA made in?
transcription
what stage of protein synthesis is tRNA made in?
translation
codon
3 adjacent bases on mRNA strand
function of tRNA
carries amino acids used to make proteins to the ribosomes
tRNA structure
single polynucleotide strand folded into a clover shape by hydrogen bonds between specific base pairs - has anticodon (sequence of 3 specific bases) at one end and amino acid binding site at the other
transcription
producing an mRNA copy of a gene from DNA (in nucleus in eukaryotes)
translation
polypeptides made at ribosomes by the joining of amino acids, following codon sequence carried by mRNA
why is the code ‘non-overlapping’?
each base only read once
why is the code ‘universal’?
with few exceptions, each triplet codes for same amino acid in all organisms
homologous pair
a pair of chromosomes, one maternal and one paternal which have the same gene loci and therefore determine the same features
structure of mRNA
long strand in single helix
- base sequence determined by base sequence of DNA
anticodon
sequence of 3 organic bases on tRNA molecule, complimentary to a particular codon on mRNA molecule
2 factors increasing frequency of mutation
- x rays
- benzene
3 differences between tRNA and mRNA
- mRNA has no base pairing, tRNA does
- mRNA linear, tRNA is clover shaped
- mRNA has no binding site for amino acids
3 possible results of substitution mutation
1 - formation of stop codon marking end of polypeptide chain, resulting in stopping of production prematurely = final protein v different
2 - formation of codon for different amino acid - finally polypeptide will differ by 1 amino acid = non functional protein?
3 - formation of codon for same amino acid - code is degenerate therefore no effect on polypeptide chain produced
deletion mutation
causes FRAME SHIFT to LEFT - reading frame for each 3 letters of code has shifted one to the left
= production of non-functional protein as all amino acids from that point may be different/affected
= alter phenotype significantly
(mutation at start bigger impact then mutation at end)
addition mutation
causes FRAME SHIFT to RIGHT
- if 3 bases or multiple of 3 added, no frame shift therefore smaller change to polypeptide chain produced, but still different to one from NON-MUTANT gene
duplication mutation
causes frame shift to right
inversion of bases mutation
group of bases becomes separate from DNA sequence and rejoins in same position but in inverse order - therefore base sequence REVERSED, amino acid sequence affected
translocation of bases
- group of bases separated from DNA on one chromosome and is inserted into DNA on another chromosome
= significant affect on GENE EXPRESSION = abnormal phenotype (development of certain cancers and infertility)
