DNA Flashcards
What are the 4 bases in DNA
ATCG
Adenine, Thymine, Cytosine, Guanine
What are the pairs of bases in DNA?
Adenine and Thymine (AT)
Cytosine and Guanine (CG)
What are the 4 ways RNA differs from DNA
RNA is single stranded, DNA is double
RNA has ribose sugar, DNA has deoxyribose sugar
RNA has the base Uracil (U) but DNA has the base Thymine
RNA is shorter than DNA
What are the two types of RNA?
mRNA - messenger RNA
tRNA - transfer RNA
What are the two stages of turning a gene into a sequence of amino acids?
Transcription - DNA is transcribed and mRNA is produced
Translation - mRNA is translated and an amino acid sequence is produced
Where does transcription take place?
Nucleus
Describe the process of transcription
Part of DNA molecule unzips.
Free mRNA nucleotides bond to complementary nucleotides of the DNA. mRNA copies DNA.
A single strand of mRNA is formed and it leaves the nucleus.
Transcription uses DNA to make RNA.
Occurs in nucleus
Where does translation take place?
In ribosomes/cytoplasm
Describe the process of translation
mRNA leaves the nucleus and attaches to a ribosome in the cytoplasm. Strand passes through ribosome
In cytoplasm there are free molecules of tRNA. For every three mRNA bases (codon) there are three complementary tRNA bases (anticodon).
Anticodon from tRNA pairs with codon on mRNA molecule. tRNA brings amino acids with it.
Peptide bonds formed between amino acids.
Polypeptide (chain of amino acids) is formed.
What are codons?
Every 3 bases on mRNA
What are anticodons?
Complementary (to codons) three bases on tRNA
What bases does RNA have?
Adenine, Uracil, Guanine and Cytosine (AUCG)
If a DNA strand has bases
CAT TCA ATT CAT
what is the complementary mRNA code?
GUA AGU UAA GUA
What are the base pairing for DNA to RNA?
DNA RNA
A - – - – > U
T ——– – > A
G — - – - -> C
C – - - — – -> G
How many bases codes for a single amino acid?
3 (a codon)
What is a mutation?
A rare, random change in the sequence of bases in DNA
What is the genome of an organism?
The entire DNA of an organism (all its genetic material)
How does a mutation affect the phenotype of an individual?
It alters the sequence of amino acids in a protein. Change in bases of DNA. Produces a different enzyme.
What are the 3 ways the sequence of DNA is changed by mutations?
Insertion of a new base into DNA sequence.
Deletion of a base within DNA sequence
Substitution of a base within the DNA sequence.
Insertion and deletion have knock-on effects to the whole protein
Do mutations always have an effect on the phenotype?
No, most don’t alter the protein.
Some can have a small effect.
A small number of mutations code for a significantly altered protein with a different shape. This can affect the protein’s ability to perform its function.
Exposure to what can increase frequency of mutations?
Gamma rays, X-rays and UV rays - ionising radiation which can damage bonds and cause base sequences to change
Chemical mutagens (such as tar in tobacco)
Explain how natural variation occurs
Variation occurs due to random and continuous mutations.
Some individuals within a population have features so they are more able to survive in the environment.
Individuals with these special features are more likely to survive and reproduce.
Advantageous alleles passed on to next generation
Offspring inherit advantageous characteristics
Repeats over many generations
Explain antibiotic resistance
Doctors begun to use penicillin, which killed the bacteria.
Mutation gave some bacteria resistance to the antibiotic
These bacteria were better adapted to survive penicillin
Resistant bacteria survived in greater numbers
Resistant bacteria reproduced rapidly and passed on resistance allele
Repeated over many generations
Describe how a mutation in DNA of a cell affects the functioning of an enzyme
Change in base sequence
Leads to different codon
Different amino acid in protein
Change to shape of active site
Explain why some mutations have little effect on the phenotype of an organism
Change in base may not affect amino acid
Amino acid may not be involved in active site
Enzyme still made
Could be recessive allele so not expressed in phenotype
