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what does DNA stand for?

deoxyribonucleic acid


What is the structure of a DNA molecule?

a phosphate
deoxyribose sugar
a base

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?

-pH buffer
- DNA template
- taq polymerase


What are the uses of PCR?

-DNA profiling
-disease detection
-population studies


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?

-single stranded
- 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
-skin grafts


What is the function of non coding regions of the genome (introns)?

-regulation of transcription
-transcription of non translated forms of RNA
- unknown


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


What is pharmacogenetics?

genetic differences which cause individuals to react differently to drugs