DNA Flashcards
Why is DNA a polynucleotide ?
It is composed of many nucleotides.
What are the main components of DNA.
2 sugar phosphate backbones held together by base pairs.
What are the 4 types of nitrogenous base pairs ?
Adenine
Thymine
Guanine
Cytosine
Which nitrogenous bases pair together.
A and T
C and G
How many hydrogen bonds do each set of nitrogenous bases create ?
A to T = 2 hydrogen bonds
C to G = 3 hydrogen bonds
What are the monomers of DNA called.
Nucleotides
What are nucleotides.
Monomers of DNA
How are nucleotides formed
Condensation reactions where water is removed and replaced by a phosphodiester bond which is created between the sugar and the phosphate in the sugar-phosphate backbone.
What is the bond between the ribose sugar and phosphate in DNA called.
Phosphodiester bond
What does a phosphodiester bond join ?
Ribose sugar and phosphate
Which molecules loose what during the formation of a phosphodiester bond ?
Ribose sugar looses OH
Phosphate looses H
What type of bond is created between the sugar and the nitrogenous base in DNA.
Covalent bond
Where is a covalent bond created in DNA
Between the sugar and the nitrogenous base.
What are the 3 types of bond in DNA and what are they between ?
Hydrogen between nitrogenous bases.
Phosphodiester between sugar and phosphate
Covalent between sugar and base
What is the final shape of DNA
Helix due to it twisting
Which nitrogenous bases are purines ?
Adenine and guanine
Which nitrogenous bases are pyrimidine
Thymine and cytosine
What does purine relate to and what does it mean.
Both adenine and guanine nitrogenous bases are purine as they have double ring shapes.
What does pyrimidine mean and what does it relate to ?
Both thymine and cytosine and pyrimidine was they have only single ring shapes.
Why are DNA strands anti parallel.
The DNA strand are anti parallel as one strand runs from carbon 3 to carbon 5. Whilst the other runs from carbon 5 to carbon 3.
What functions of DNA give it the ability to carry out its function ?
Coiling makes it compact
Sugar to phosphate backbone gives strength
Long molecules store a lot of information
Complementary base pairing enables information to be replicated
Double helix protects hydrogen bonds and makes the molecule stronger
Many hydrogen bonds create stability and prevent code corruption
Hydrogen bonding allows chain to split for replication.
Describe in detail how DNA is replicated.
- DNA helicase unwinds the DNA and breaks the hydrogen bonds.
- The two strands of DNA separate and are stabilised by binding proteins.
- Free nucleotides approach the exposed bases of both strand. The complementary base pairs form hydrogen bonds.
- DNA polymerase joins the new nucleotides together by condensation reactions to form a new strand.
- Each new molecule is an exact copy of the original. With one old parent strand and one newly-synthesised daughter strand.
- The molecule twists into a helix.
- This is semi-conservative replication.
Why is DNA replication known as semi-conservative ?
When DNA replicated one strand of each molecule is the old parent strand and one is the newly-synthesised daughter strand.
Half remains
What is an allele ?
A version of a gene with a different base sequence.
What does each gene contain ?
A sequence of bases which code for a sequence of amino acids which build a protein.
How many different gene code combinations are there ?
64
Which triplet code always start a polypeptide chain ?
Methionine
What type of amino acids mark the end of an amino acid sequence ?
Codons
What are Exons ?
Sections of DNA that code for amino acids.
What are introns ?
Sections of DNA which don’t code for amino acids.
What are sections of DNA that code for amino acids called ?
Exons
What are sections of DNA that don’t code for amino acids called ?
Introns
Why are gene codes often referred to as degenerate ?
More than one codon can code for one amino acid.
Why are gene codes often referred to as universal.
The code is the same in all organisms and no-overlapping occurs.
Where are polypeptide chains made ?
The ribosomes as they are proteins
How would a change in one base result in an enzyme becoming non-functional ?
The change of primary structure amino acids would alter the hydrogen, ionic and phosphodiester bonding. This therefore changes the tertiary structure meaning the active site changed shape.
The active site is no longer complimentary to the substrate and no enzyme-substrate complex can be made.
What is meant by a degenerate gene code ?
One amino acid can be coded for by more than one triplet.
What is a codon ?
Three bases of MRNA.
What is the role of RNA polymerase during transcription?
Joins nucleotides together to form mRNA
What enzyme converts mRNA into cDNA ?
Reverse transcriptase
Name the organelle involved in translation.
Ribosomes
Describe the role of tRNA in translation.
The anticodon is complementary to the codon and reads the message on the mRNA. It is specific to the amino acids. The correct sequence of amino acids is therefore carried along the polypeptide.
Give two ways in which the structure of a molecules of tRNA differs from the structure of a molecule of mRNA.
tRNA is a clover leaf shape and is a standard length. It has an amino acid binding site and has three exposed base pairs meaning an anticodon is available tRNA has hydrogen bonds between base pairs.
Give two factors which might increase the frequency at which mutations in DNA may occur.
High energy radiation from sources such as X-Rays, ultraviolet light, gamma rays, alpha particles and beta particles. Also chemicals such as benzene and caffeine, Tabacco tar, free radicals.
Starting with mRNA describe how the process of transcription leads to the production of a polypeptide.
mRNA codon attaches to the ribosomes. This then bonds to the anti-codon on the tRNA. Each tRNA brings a specific amino acid. The sequence of codon bases determined the order of amino acids and the formation of peptide bonds. These amino acids are joined by condensation reactions.
What sugar is in DNA ?
Deoxyribose
What sugar is in RNA ?
Ribose sugar.
Give 2 types of pentose sugar.
Deoxyribose and ribose
Compare the structures of DNA and RNA
DNA is a deoxyribose sugar with double helix and had the bases A,T,C and G.
RNA is a polynucleotide with a single strand and contains ribose sugar. It contains the bases A,U,C and G.
What bases do MRNA and TRNA Ickes
AUCG
What is the function of mRNA and how does it carry out this function ?
MRNA transfers DNS code from the nucleus to the cytoplasm. It is small enough to leave the nucleus via the nuclear pores and contains coded information to determine the sequence of amino acids in protein synthesis during translation.
How many codon bases make up one amino acid ?
3
What is the function of tRNA and how does it carry out this function ?
Carries amino acids that are used to make proteins from the cytoplasm to the ribosomes.
Describe the structure of tRNA.
It is a clover shape due to the single strand polynucleotide being folded and held into shape by hydrogen bonds.
They all have a 3 base anticodon at one end and an amino acid binding site at the other end.
What are at each end of tRNA ?
One side: a 3 base anticodon
Other side: an amino acid binding site.
How long does tRNA tend to be ?
73-94 nucleotides long.
Describe the length of mRNA
Varying.
What is the definition of a codon ?
The sequence of triplet bases that code for one amino acid in mRNA.
What is the definition of genome ?
The complete set of genes in a cell
What is the definition of proteome ?
The full range of proteins produced by a gene.
Summaries how the DNA required to synthesise proteins is removed from the nucleus and goes to the ribosomes.
The DNA in the nucleus is too large to leave. Therefore a strand of DNA is copied forming messenger RNA (mRNA).
Then mRNA leaves the nucleus and travels to the ribosomes where it is transcribed.
Describe stage one of transcription
DNA double helix unzips using DNA helicase. Hydrogen bonds between complimentary base led break and the 2 polynucleotide strands separate.
Describe stage 2 of transcription.
Sense strand acts as a template. Free RNA nucleotides create hydrogen bonds with the exposed complimentary base pairs. RNA polymerase joins the RNA nucleotides together to form a new strand of mRNA.
Describe stage 3 of transcription
Pre-MRNA detaches from the sense strand. The 2 DNA strands join together by complimentary base pairing. DNA molecule winds back up into helix.
Describe the post transcriptional modifiction/ splicing process.
Genes containing non-coding regions are called introns. Introns must be removed from MRNA or there will be gala in the polypeptide chain. They are removed by an enzyme. The mRNA then leaves the nucleus.
What is the name of a gene type which does code ?
Extron
What is the general name for a gene which doesn’t code
Intron
What are extrons
Genes which code
What are introns
Genes which don’t code
What is alternative splicing ?
Many Exons can be arranged in many ways to create numerous different polypeptides.
What causes antibodies to have variety binding sites ?
Alternative splicing where one sequence of DNA with many Exons can be arranged in different ways to make varient polypeptides
What is an allele ?
A form of a gene which determines characteristics
Outline the main differences between DNA replication and transcription.
Transcription uses the base Uracil whereas DNA replication uses Thymine.
In DNA replication all DNA is copies. In transcription only specific areas of the DNA are copied.
DNA replication uses 2 strands whereas transcription only uses one strand.
In DNA replication DNS polymerase is used to bind strands whilst in transcription RNA polymerase is used.
Outline the similarities between DNA replication and transcription.
Both use DNA polymerase
Both use complimentary base pairing.
Both have hydrogen bonds between complimentary base pairs.
What is the role of RNA polymerase during transcription ?
To bind to nucleotides together to form mRNA.
What is a codon.
Threee based of mRNA.
What is Translation ?
Conversion of the sequence of bases in MRNA to the sequence of amino acids in a polypeptide chain.
Where does translation occur ?
At the ribosomes.
Describe in detail the process of translation.
- the tRNA molecules, which have amino acids attached move to the specific codon which is complimentary to their anticodon. These codons are on the mRNA and hydrogen bonds are then formed between complimentary base pairs.
- A second tRNA makes complimentary base pairs with the next codon.
- ATP and an enzyme forms a peptide bonds between the 2 amino acids which have been carried by each of the tRNA molecules.
- The first tRNA then leaves to pick up another amino acid from the pool in the cytoplasm.
- The ribosome moves along the mRNA strand by 1 codon.
- This then repeats as a 3rd tRNA molecules forms a complimentary base pair with the next codon …..
- This process continues until the mRNA strand reaches a stop codon.
What happens if additional ribosomes are added during the process of translation ?
Many polypeptides are made from one tRNA molecule.
What are mutations ?
Changes in the base sequence of are DNA.
Name some causes of mutations
UV light
X-rays
Carcinogens such as cigarettes
Name the 2 types of mutation and explain both
Substitution/ bass mutation where one base is swapped for another
Deletion/ addition frame shift mutation
Removing or adding a base to the DNA sequence and therefore completely changing the polypeptide chain
What is a nonsense mutation ?
Substitution of a base leads to a premature stop codon. Successful synthesis of the final protein is unlikely.
What is a Mis-sense mutation ?
A substitution in base leads to one different amino acid. If this amino acid determines the active site of the enzyme, it could become non-functioning. But if not you will have the same enzyme.
What is a silent mutation ?
Substitution of bases but still code for the same amino acid.
Same polypeptide produced.
Describe natural selection and how it works.
Usually increase genetic diversity.
Increases advantageous alleles in population.
Randomly occurring mutations sometimes result in a new allele being formed. These new alleles can be harmful mutations and therefore quickly die out.
Describe genetic bottlenecks and how they work.
Genetic bottlenecks reduce genetic diversity as they reduce different alleles in the gene pool.
Something happenes to reduce the population of a species significantly. One group may have a beneficial allele to help survival and the group will survive whilst the others die out.
Survivors will reproduce and a population is created of individuals with reduced genetic diversity.
Describe the founder effect and how it occurs.
Decreases genetic diversity- is a type of genetic bottleneck.
Small number of different alleles in the gene pool. Frequency of each allele in the new colony is different to the frequency of alleles in the different population. The lack of variant alleles creates genetic disorders.
Describe evolution as part of genetic diversity.
Organisms with beneficial genes survive longer and mate therefore beneficial alleles are passed onto the next generation so they have greater proportions of inheriting genes. Over generations this leads to evolution as the advantageous alleles become more common in the population.
Define population
Group of organisms of one specific that live in a particular habitat.
Define genetic diversity.
Number of didfefent alleles of genes in a species or population.
Define allele.
Different versions of a single gene.
What are the 2 ways genetic variation can be increased.
Random mutations - in the DNS forming new alleles.
Different alleles- introduced into a population caused by migration of individuals from another population reproducing with another. This is gene flow
What is gene flow.
Individuals from one population reproduce with individuals from another population.
What are the 3 types of selection ?
Behavioural
Anatomical
Physiological
What is behavioural selection ?
Acts which an organisms does to increase chances of survival.
What is anatomical selection ?
Structural features which increase an organisms chances or survival.
What is physiological selection ?
Processes inside an organisms body which increase chances of survival.
What are phenotypes ?
Characteristics.
What are polygenes ?
These types of phenotypes that give normal distribution curves are influenced by more than one gene. These can be heavily influenced by the environment.
Give examples of polygenes
Mass , height, number of leaves
What are the 2 types of genetic selection.
Directional and stabilising
What is directional selection ?
Individual with alleles for phenotypes of an extreme type are more likely to survive and reproduce.
What is stabilising selection ?
Individuals with alleles for phenotypes towards the middle of the range are more likely to survive and reproduce.
Compare directional and stabilising selection.
Directional selects extreme phenotypes. Stabilising selects phenotypes around the mean.
Directional changes characteristics of population. Stabilising preserves characterises.
Directional causes the distribution curve to stay the same however the mean moves left or right. Stabilising causes the distribution curve to get narrower and higher but the mean remains the same.
How does directional selection affect a distribution curve ?
Dirtibution curve remains the same but the mean shifts left or right.
How does stabilising selection affect a distribution curve ?
Distribution curve gets narrower and higher but the mean remains the same.
