DNA & Genetic Diversity

similarities and differences between DNA and RNA

similarities and differences between DNA and RNA

Sim:

both are polynucleotides (many nucleotides linked together in a long chain)

both contain nitrogenous bases: adenine guanine and cytosine and have phosphodiester bonds

diff:

RNA nucleotides never contain nitrogenous base Thymine (Uracil instead)

RNA contains pentose sugar ribose instead of deoxyribose (that DNA contains)

RNA molecules are only made up of 1 polynucleotide strand (single stranded)

what are nucleotides made from

• pentose sugar ( 5 carbon sugar)

• nitrogen containing organic base

• phosphate base

what bonds are between bases and nucleotides?

hydrogen bonds between bases

phosphodiester bond between nucleotides

structure of DNA and its nucleotides

• polynucleotide

• 2 polynucleotide strands joined together with hydrogen bonds forming a double helix

  Each DNA nucleotide has:

• deoxyribose sugar

• phosphate group

• one of four nitrogenous bases: cytosine, thymine, adenine, guanine

7 structures of DNA and their functions

• sugar phosphate backbone - gives strength

• helix - gives compact shape and protects sequence of bases

• double stranded - each strand serves as a template in replication; protects sequence of bases ; makes molecules more stable

• large molecule- large amount of information can be stored

• many hydrogen bonds - gives stability; individual hydrogen bonds are weak, allowing helix to unzip easily for replication

• sequence of bases- codes for specific sequence of amino acids in polypeptide

• complementary base pairing- enables information to be replicated accurately

What are genes and what do they do?

sequence of nucleotide bases in a DNA molecule that codes for the production of a specific sequence of amino acids that in turn make specific polypeptides (proteins)

why can DNA self replicate?

due to complementary base pairing essential for cell division

How does variation occur? (genetic diversity)

random mutations

random fusion of genetically different gamete (fertilisation)

independent segregation of homologous chromosomes

crossing over of homologous chromosomes

mutagenic agents (env

describe stages of semi-conservative mechanism of DNA replication

• As DNA replicates , the enzyme DNA helicase breaks the hydrogen bonds and seperates the two polynucleotide strands

• Each strand acts as a template for formation of 2 new complementary strands

• individual DNA nucleotides align and attach by hydrogen bonding to the exposed bases of each template strand according to specific complementary base pairs

• A-T C-G

• DNA nucleotides in each new strand are joined together by phosphodiester bonds in condensation reactions catalysed by enzyme DNA polymerase

• 2 new DNA molecules are identical to each other and to the original DNA

why does it get the name semi conservative?

Each newly formed DNA molecule contains one original polynucleotide strand and one new strand hence the name

what evidence is there to show replication is semi conservative

two scientists Meselson and Stahl conducted these experiments

• grew bacterium in which 14N was replaced with 15N

• cells were allowed to divide until it was certain that 15N had been incorporated into entire DNA

• bacteria were then transferred to a medium containing only the normal isotope 14N and allowed to divide

• samples of bacteria were then taken after each division (generation) & DNA was extracted and spun into a centrifuge. DNA containing the heavy isotope 15N is slightly heavier than DNA containing the normal 14N isotope.

structure of RNA

• relatively short polynucleotide molecule

• pentose sugar ribose

• organic base uracil replaces thymine

• single stranded (mRNA and tRNA) compared to double stranded DNA

describe structures and functions of mRNA and tRNA.

mRNA:

• linear structure and contains codons (mRNA base triplets)

• single stranded molecule and shorter/ smaller than DNA so it can leave the nucleus through the pore

• exposed unpaired bases

• made up of sugar phosphate backbone

• Uracil bases present instead of Thymine

  function

• found in nucleus and makes copies of the DNA template so that it can leave the nucleus

• involved in protein synthesis and formed in nucleus during transcription

tRNA-

• single stranded molecule

• has a sugar phosphate backbone

• folded clover leaf shape - hydrogen bonds between some of the complementary bases

• amino acid binding site on a specific region of the molecule

• specific anicodon on tRNA (three unattached tRNA nucleotide bases) are complementary to specific codon on mRNA molecule

  function

• found in the cytoplasm and used during translation to deliver specific amino acids to the ribosome to create a polypeptide

• they already exist in the cytoplasm and doesn’t have to be created ( there are 20 different tRNA molecules)

differences between mRNA and tRNA

mRNA

• linear

• posseses codons

• no hydrogen bonds (but there are phosphodiester bonds

• no amino acid binding site

• exposed bases

tRNA

• folded clover leaf shape

• posseses anitocodons (free nucleotides)

• hydrogen bonds present

• amino acids binding site present

DNA in prokaryotes vs eukaryotes

role of histones? and other proteins in eukaryotes?

properties of plasmids ?

eukaryotes:

• DNA molecules associate with proteins called histones to form chromosomes during cell division.

• chromosomes are made of one very long, condensed DNA molecule (in eukaryotic cells)

• histones’ role is to organise and condense the DNA tightly to fit in the nucleus

• other proteins are enzymes used in copying and repairing the DNA

• eukaryotic DNA also contains introns

prokaryotes:

• DNA is double stranded

• prokaryotes possess a single, circular chromosomal DNA molecule

• usually have one or more plasmids (very small circular DNA molecules)

• DNA within prokaryotic cells is not associated with any proteins

• plasmids are small circular DNA and usually only contain few genes; more accessible for proteins required for gene expression and therefore contain genes required often, quickly/ for emergencies; genes for antibiotic resistance are often found in plasmids

what are chromosomes

one very long, condensed DNA molecule associated with histones(proteins)

what are homologous pairs of chromosomes

pair of chromosomes: one inherited from father and one from mother (maternal and paternal)

they carry the same genes in the same loci but not necessarily the same allele

what is a locus

position of a gene on a chromosome. alleles occupy the same locus on each member of a pair of homologous chromosome.

what is a sequence of three nucleotides called and what do they code for

three DNA nucleotide bases : base triplet (template for mRNA)

three mRNA bases: codon (complementary to tRNA) complementary to triplet

three tRNA bases: anticodon (codes for specific amino acids) complementary to codon → same as DNA except for base URACIL which replaces THYMINE

what are the qualities of triplet codes?

• degenerate

• non overlapping

• universal

what does a degenerate triplet code mean

different triplets/ codons coding for the same amino acid

what does non overlapping code mean?

each base only read once as part of a specific triplet

what does universal code mean?

same triplets code for the same amino acids in all organism

what is the purpose if start and stop triplets?

ensures cell reads DNA correctly and produces the correct sequence of amino acids required for the polypeptide to function properly

what are some non coding DNA

Introns

multiple repeats

what do introns and multiple repeats mean?

introns: base sequence present within genes that dont code for amino acids

withIN genes that INterrupt coding

multiple repeats: some base sequences present between genes (contain same base sequences repeated multiple times)

what is an exon?

sequences in genes that code for amino acids (usually separated by 1 or more introns)

what is a genome

complete set of genes (non coding DNA included) in a cell

extra information on genome

always a full genome present in every cell of organism

however not every cell is expressed in every cell

which genes are expressed are dependent on cell type

what is a proteome

full range of proteins that a cell is able to produce

more information on proteome

larger than genome of organism because of large amount of post transitional modification of proteins

each gene is also capable of producing multiple different proteins (alternative splicing)

resulting in larger proteome than genome

Quickly describe transcription and translation

Transcription: DNA is transcribed and an mRNA molecule is produced (occurs in nucleus)

Translation: mRNA is translated and an amino acid sequence is produced (cytoplasm)

Describe and explain transcription

• DNA molecules unwind (hydrogen bonds broken between complementary base pairs) by DNA helicase

• exposes gene to be transcribed

• complementary copy of the code from the gene is made by a single stranded mRNA molecule

• only ONE of the strands acts as a template

• free activated RNA nucleotides pair up via (hydrogen bonds) with their complementary bases (now exposed) on one strand of the unzipped molecule

• sugar phosphate groups of these RNA nucleotides are then bonded together by enzyme RNA polymerase to form the phosphodiester bonds in the mRNA molecule.

• once gene is successfully transcribed, and mRNA molecule is complete, hydrogen bonds between mRNA and DNA strands break and double stranded DNA molecule reforms

• mRNA molecule leaves nucleus via pore in envelope

splicing?

occurs before pre-mRNA leaves nucleus

• non coding sections are removed (introns and multiple repeats)

• coding sections are joined together

• resulting in mRNA molecule carries only coding sequences (exons) of gene

• mRNA contains ONLY exons

describe and explain translation

• mRNA molecules attach to a ribosome

• in the cytoplasm there are free molecules of tRNA

• tRNA have anticodons (unpaired triplet bases) and a region where specific amino acids can attach to

• there are approximately 20 different tRNA molecules with specific anticodons and amino acid binding site

• tRNA molecules bind with their specific amino acid and bring to ribosome and mRNA molecule

• each anticodon on each tRNA molecule pairs with complementary codon on mRNA molecule

• 2 tRNA molecules can fit in a ribosome at a time bringing each amino acid they carry

• peptide bonds form between 2 amino acids

• which requires ATP provided by mitochondria

• process continues until ‘stop’ codon on mRNA is reached and a specific polypeptide is produced

what is genetic diversity?

number of different alleles in a population

what are gene mutations and what types are there?

changes in sequence of nucleotide bases in DNA resulting in altered polypeptide. NEW ALLELES of genes are produced

• Deletion of nucleotides - removal of one it more bases results in frame shift. sequence of amino acids is altered from point of mutation and protein formed nearly always non-functional

• Substitutions: replacement of one or more bases by one or more different bases. only changes amino acid for the triplet ( wont have a knock on effect) non functioning protein may form due to different amino acids in polypeptide

what are alleles?

what is mitosis

what is meaning of diploid and haploid numbers?

what is cell cycle divided into?

describe further stages of mitosis

describe further stages of mitosis

describe interphase and cytokinesis

what is cancer and how is it treated?

Describe and explain meiosis. When is it used?

what are differences between mitosis and meiosis?

what is process of meiosis?

what causes genetic diversity during meiosis

how do chromosome mutations occur + explain

describe principles of natural selection

what are the adaptations species may have to be better suited for survival?

Name + describe and explain different types of natural selection