DNA and Genetic Diversity Flashcards
1
Q
what is a nucleotide formed from
A
- phosphate group
- pentose sugar
- nitrogenous base
2
Q
What is the structure of DNA and who discovered it
A
- discovered by Watson and Crick
- consists of two polynucleotide strands joined together by hydrogen bonding to form a double helix
- phosphodiester bonds between nucleotides formed in condensation reactions
3
Q
How does DNA replicate
A
semi - conservative replication:
- DNA helicase unzips the 2 strands by breaking the hydrogen bonds and both strands become templates
- free nucleotides are attracted to complimentary bases on the templates by hydrogen bonding
- once the nucleotides are lined up they are joined together by phosphodiester bonds by DNA polymerase via condensation reactions
- 2 identical molecules of DNA are formed each one composed of one original strand
4
Q
What are some functions of DNA
A
- genes are sections of DNA that code for a specific sequence of polypeptide determining the nature and development of organisms
- DNA has the ability to self replicate which is essential for cell division
- changes in the base sequence (mutation) could occur, providing genetic diversity
5
Q
How do bases in nucleic acids pair with each other
A
- complementary base pairing through hydrogen bonding
- Adenine always pairs with Thymine ( T replaced by Uracil in RNA)
- Guanine always pairs with Cytosine
6
Q
similarities in structure of prokaryotic DNA and eukaryotic DNA
A
similarities:
- nucleotide structure is identical in both
- nucleotides are joined by phosphodiester bonds in both
7
Q
How is the structure of DNA related to its function
A
sugar - phosphate backbone gives strength
(coiling gives) compact shape
long molecule stores large amount of information
(double helix protects) weak hydrogen bonds / double helix makes molecule stable prevents code being corrupted
chains held together by weak hydrogen bonds; chains can split for replication / transcription
8
Q
differences in structure of prokaryotic DNA and eukaryotic DNA
A
differences:
- eukaryotic DNA is longer
- eukaryotic DNA = linear , prokaryotic DNA = circular
- introns only in eukaryotic DNA
- eukaryotic DNA associated with proteins prokaryotic DNA not
9
Q
what is some evidence for semi conservative replication
A
- Meselson and Stahl showed that replication is semi conservative
- they grew bacterium E. coli on a medium in which the normal isotope ¹⁴N was replaced with the heavy isotope ¹⁵N
- the cells were allowed to divide until it was certain that ¹⁵N had been incorporated into the entire DNA
- the bacteria were then transferred to a medium containing only the normal isotope ¹⁴N and allowed to divide
- sample of bacteria were then taken after each division (generation) and the DNA was extracted and spun in a centrifuge. DNA containing the heavy isotope ¹⁵N was slightly heavier than DNA containing the normal isotope ¹⁴N
10
Q
what are multiple repeats in DNA
A
short base sequences between genes repeated over and and over again.
11
Q
differences in structure of RNA to DNA
A
- DNA contains deoxyribose, RNA contains ribose
- the base Thymine in DNA is replaced with Uracil in RNA
- mRNA and tRNA are single stranded in comparison to double stranded DNA
12
Q
similarities in structure of RNA and DNA
A
- both contain nitrogenous bases
- both have a phosphate group
13
Q
similarities in structure between mRNA and tRNA
A
- both contain the same bases
14
Q
differences in structure between mRNA and tRNA
A
- mRNA has linear structure, tRNA has clover leaf structure
- mRNA possesses codons, tRNA possesses anti-codons
- mRNA has no amino acid binding site, tRNA does
15
Q
what is mitosis
A
- cell division producing two genetically identical daughter cells
16
Q
what is a homologous pair of chromosomes
A
- a pair of chromosomes which carry the same gene in the same loci but not necessarily the same allele
17
Q
what is a base triplet
A
a sequence of three nucleotide bases that code for a specific amino acid
18
Q
what is an allele
A
different forms of a gene
19
Q
what is a codon
A
base triplets in mRNA
20
Q
what are introns and exons
A
- exons are base sequences in genes that do code for amino acids
- introns are base sequences present within genes that do not code for amino acids
21
Q
what is a gene mutation and what are the 6 different types
A
gene mutation - changes in the sequences of the nucleotide bases in the DNA
types :
- substitution
- deletion
- addition
- duplication
- inversion
- translocation
22
Q
describe 3 features of the genetic code
A
degenerate triplet code - some amino acids are coded for by more than one triplet
non overlapping code - each base is only read once as part of a specific triplet
‘universal’ code - the same triplets code for the same amino acids in all organisms
23
Q
what is a genome and proteome
A
genome-complete set of genes in a cell.
proteome-full range of proteins that a cell is able to produce.
24
Q
how is pre mRNA modified into mRNA
A
By splicing the pre mRNA
- the pre-mRNA is spliced to removed the introns and joining the exons together to form mRNA
25
describe the process of transcription
- the relevant section containing the gene uncoils and is unzipped by DNA helicase as the hydrogen bonds break
- one of the two strands act as a template as free RNA nucleotides line up alongside the DNA nucleotide bases on the template by complementary base pairing
- free RNA nucleotides are then joined together with phosphodiester bonds in reactions catalysed by RNA polymerase producing pre mRNA
26
describe the process of translation
- mRNA attaches to the ribosome in the cytoplasm and a tRNA molecule with the complementary anticodon base sequence binds to the first codon on the mRNA strand at the ribosome, ribosome has two binding sites so two tRNA molecules will bind to two codons on the mRNA within a ribosome.
- the amino acid on the 1st tRNA molecule is attached to the 2nd amino acid by a peptide bond in a condensation reaction
- the 1st tRNA molecule leaves the ribosome, leaving the amino acid behind and collects another molecule of the same amino acid from the 'amino acid pool' in the cytoplasm
- the ribosome moves along the mRNA strand until all codons have been read up to the stop codon and the polypeptide has been produced. It then folds itself into its secondary and tertiary structures.
27
what is a frame shift
change resulting in misreading of all nucleotides downstream, usually resulting in a truncated non-functional protein
28
what type of mutations cause a frame shift and explain them
deletion - the removal of 1 or more bases resulting in a frame shift
addition - the adding of one or more bases resulting in a frame shift
duplication - where one or more bases is repeated causing a frame shift
29
what type of mutations don't cause a frame shift and explain them
inversion - a sequence of bases is reversed e.g. TAGCAGCT becomes TCGACGAT
translocation - a sequence of bases is moved from one location in the DNA molecule to another part of the genome
substitution - the replacement of one or more bases by one or more different bases
30
what is the diploid number
the total number of chromosomes in a normal body cell ( in humans it's 46)
31
why can a functioning protein still be formed after substitution
- the DNA code is degenerate meaning that an amino acid can be coded by more than 1 base triplet
- the mutation could have occured in an intron which doesn't code for proteins
- the mutation doesn't affect the shape of the tertiary in a way that affects the function of the protein
32
what is the haploid number
it represents a single set of chromosomes ( in humans it's 23)
33
What are the stages of the cell cycle?
IPMAT
interphase
mitosis (prophase, metaphase, anaphase, telophase)
cytokinesis
34
what happens in interphase?
- DNA replicates ( each chromosome now made of 2 sister chromatids)
- increase in protein synthesis
- cell organelles are replicated e.g. mitochondria + ATP content increased for energy as cell division is an active process
35
what happens in mitosis
Prophase
- chromosomes condense (shortens and thickens)
- Nuclear membrane disintegrates
- Centrioles move to opposite poles
Metaphase
- centrioles in animal cells form a spindle (consisting of protein microtubules) across the cell
- chromosomes line up in the middle of the cell
Anaphase
- sister chromatids split and are pulled to either pole via the spindle microtubules
Telophase
- at opposite poles of the cell the chromatids begin to uncoil
- the nuclear membrane reforms
36
What happens in cytokinesis?
- the cytoplasm splits in two
- two new cells form
37
what is a common cause of cancer
damage to the genes that regulate mitosis and the cell cycle resulting in uncontrolled cell division and growth
38
difference between mitosis and meiosis (4)
- mitosis has one nuclear division, meiosis does two
- mitosis produces two daughter cells, meiosis produces four
- mitosis produces genetically identical cells, meiosis doesn't
- mitosis produces cells with the same amount of chromosomes as the parent cell, meiosis produces cells with half
39
what is crossover during meiosis
- the pair of homologous chromosomes lie side by side forming a bivalent
- the chromatids of the homologous chromosomes then intertwine
- the chromatids break and equivalent portions of the chromatids are exchanged
40
how is variation (genetic diversity) achieved during meiosis
- independent segregation of homologous chromosomes
- genetic recombination (crossover) within homologous chromosomes
41
how do you calculate the possible numbers of varied combinations of paternal and maternal chromosomes
2ⁿ
- n = number of homologous pairs
42
what is independent segregation during meiosis
- during the first meiotic division, hom. chromosomes pair together and then separate so that one member from each pair enters the gamete
43
what is a chiasma
site of crossing over
44
what is genetic recombination
the exchange of alleles ,during cross over, producing new combinations of alleles known as recombinants
45
what are the three types of adaptations
-anatomical
-physiological
-behavioural
46
what is nondisjunction
the failure of the chromosomes to separate during cell division , which produces daughter cells with abnormal numbers of chromosomes.
47
what are the 4 principles of natural selection
-variation within the population is already present due mutation
-change in environment
-differential reproductive success (organisms with the advantageous phenotype survive and reproduce)
-advantageous allele increases in frequency within the population
48
describe how directional selection occurs
- due to random mutations a few organisms of a species possess an advantageous allele
- organisms with the advantageous allele are more likely to survive than others and therefore reproduce and pass on the advantageous allele
- therefore the frequency of the advantageous allele would significantly increase in the population over generations
49
describe how stabilising selection occurs
- natural selection favours organisms with alleles for characteristics towards the middle of the age
- these organisms are more likely to survive than others and therefore reproduce and pass on the advantageous allele
- therefore the frequency of the advantageous allele would significantly increase in the population over generations
