Flashcards in Unit 1 Deck (51):
what does DNA stand for?
What is the structure of a DNA molecule?
5' end joins to the 3' end
strands are anti parallel
strands are held together by hydrogen bonds
nucleotides are held together by covalent bonds
What are the base pairing rules?
adenine with thymine
guanine with cytosine
What is the organisation of DNA in prokaryotes, yeast, mitochondria and chloroplasts, and eukaryotes?
prokaryotes - circular double stranded chromosome and plasmid
yeast- circular plasmids
mitochondria and chloroplasts - circular chromosomes
eukaryotes - linear chromosomes
What is supercoiling?
Nucleosomes form - dna wraps around histone proteins
Thick chromatin fibre - chain of nucleosomes folds into chromatin fibre
Looped fibres - chromatin fibre folds again to form looped fibres
more folds - folds more to condense chromosome
What is semi conservative replication?
half of the new DNA strand comes from the original strand and the other half is new
What are the required resources for DNA replication?
DNA - to act as a template to copy
nucleotides - to form the new strand of DNA
ATP - energy for it to take place
DNA polymerase - adds complementary nucleotides to the 3' end of the strand
Ligase - joins fragments of DNA together
primer - starts replication by allowing DNA polymerase to attach
How is DNA replicated in the leading strand?
- a replication fork forms to unzip the DNA and break the hydrogen bonds
-primer attaches to the start of the DNA being copied
- DNA polymerase attaches free nucleotides to the 3' end of the primer and continues until the DNA is copied
How is the lagging strand in DNA replicated?
- many replication forks form along the DNA
- primers attach to the 3' end of these forks
- nucleotides are added by DNA polymerase
- the nucleotide fragments are joined together by ligase
What is PCR?
polymerase chain reaction is a technique for the amplification of DNA in vitro
What are the resources needed for PCR?
- DNA template
- taq polymerase
What are the uses of PCR?
What are the steps of PCR?
- DNA is heated to 92°C which causes the hydrogen bonds to break
- DNA is cooled to 55°C so that primers can anneal to the target sequence
- DNA is heated to 72°C to allow taq polymerase to add nucleotides to the 3' end
- Repeat the process again for 20-30 cycles
What is the structure of mRNA?
- ribose sugar (not deoxyribose sugar)
- bases are adenine, uracil, cytosine, guanine
What is the functions of different RNA?
- mRNA carries complementary DNA from nucleus to the ribosome
- tRNA carries free nucleotides to the ribosome to build proteins
-rRNA combines with proteins to form the ribosome
What is transcription and its requirements?
The synthesis of mRNA from a section of DNA.
Transcription needs a promoter (where transcription starts) and RNA polymerase
What is RNA splicing?
Where the mRNA strand is cut up and the introns are removed from the strand. The exons are spliced (stuck) together, resulting in mature transcript.
What is translation and its requirements?
translation is the synthesis of protein
translation needs mRNA, tRNA, amino acids and ribosomes
What are the steps of translation?
- the ribosome binds to the 5' end of the mRNA
- a tRNA carrying an amino acid/anti-codon specific to the mRNA codon becomes attached to the binding site
- the mRNA codon bonds with the tRNA anti-codon
- the ribosome moves along one codon to add the next tRNA anti-codon, where a peptide bond forms between the anti-codons
- the tRNA is released
- anti-codons are added until the ribosome reaches the stop codon and a polypeptide is formed
Where does transcription and translation take place?
transcription - mRNA is made in the nucleus and moves to the ribosome
translation - happens in the ribosome
What is alternative RNA splicing?
different sections of RNA can be treated as exons and introns so that a different mature transcript is made and thus a different protein is made
What is post translational modification?
changing the final protein after translation
-cleavage: cutting sections of the polypeptide using enzymes to make it 'active'
-addition of other molecules: carbohydrates and phosphates can be added
What is cellular differentiation?
a stem cell develops a specialised function
What are meristems?
unspecialised cells in plants that can undergo mitosis
-apical meristem: found in tip of root and shoot
-lateral meristem: found inside perennial plant and is called cambium
What is pluripotent?
a cell that can differentiate into any type of cell
What is multipotent?
a cell that can differentiate into a limited range of cell types
What can stem cells be used for?
-research on cell processes
-bone marrow transplants
What is the function of non coding regions of the genome (introns)?
-regulation of transcription
-transcription of non translated forms of RNA
What is a mutation?
a random change in the genome
What is a single gene mutation?
a change to one nucleotide in the DNA sequence eg deletion
What is a frameshift mutation?
nucleotides are moved up by at least one which changes the 'reading frame' for transcription
What is a missense, nonsense, and splice site mutation?
Missense: when substitution results in one changed amino acid, which makes a different but functioning protein
Nonsense: codes for a stop codon and results in a non functional protein
splice site: some introns are left in the mature transcript and ends up coding for a different protein
What is a chromosome mutation?/
a change in the structure of one or more chromosomes
What does polyploidy mean?
the duplication of all chromosomes resulting in extra sets of chromosomes
What does evolution mean?
changes in the organisms over generations as a result of genomic variations
What is vertical gene transfer?
genes are transferred from parents to offspring. This can be sexual of asexual reproduction.
What is horizontal gene transfer?
exchanging genetic material from one organism to another unrelated organism
Name examples of horizontal gene transfer
Transformation: DNA fragments are taken up by a prokaryote and can then be inherited by offspring.
Conjugation: a temporary connection forms between two prokaryotes. The plasmid DNA is copied to the other.
Transduction: a virus created in a host contains some of its DNA. as it spreads to other organisms the DNA enters them too.
What is natural selection?
the increase in frequency of DNA sequences that increase survival and decrease in ones that dont
How does natural selection work?
1. more offspring than the environment can support
2. all members show variation
3. many die before they reproduce
4. better adapted will survive and breed and pass adaptions onto offspring
What is sexual selection?
increase in frequency of DNA sequences that increases the chance of reproduction
In what ways does sexual selection operate?
Male to male competition: males compete for females. The stronger and larger ones will reproduce
Female choice: females will choose a male of high quality based on traits displayed
What kinds of selection are there?
Stabilising - everything gets closer to the average, less diversity
Directional- average shifts away
Disruptive- moves towards extremes in two separate populations
What is genetic drift?
the random increase/decrease in frequency of sequences because of a small population
What are neutral mutations?
there is no change to the final protein after the mutation has taken place
What is founder effects?
when a small population is isolated it will become a population with little variation
What is speciation?
the generation of a new species by evolutionary change
What are the types of speciation?
Allopatric- geographical barrier eg sea
Sympatric- ecological or behavioural barrier
What is bioinformatics?
the sequencing of DNA using computers
What is phylogenetics?
a method used to find how long ago a last common ancestor existed