DNA Flashcards
1
Q
What is DNA?
A
- deoxyribonucleic acid
- important information carrying molecule
- holds genetic info
2
Q
What is RNA?
A
- important information-carrying molecules
- transfers genetic info from DNA to ribosome
- ribosomes are formed by RNA and proteins
3
Q
DNA structure (prokaryote + within organelle)
A
- short, circular structure
- not associated with proteins
4
Q
DNA structure (eukaryote)
A
- in the nucleus
- very long and linear
- associated with proteins called histones
- together, a DNA molecule and its associated proteins form a chromosome
5
Q
Components of a DNA nucleotide
A
- deoxyribose
- a phosphate group
- one of the organic bases (adenine, cytosine, guanine or thymine)
6
Q
Components of RNA nucleotide
A
- a ribose
- a phosphate group
- one of the organic bases (adenine, cytosine, guanine or uracil)
7
Q
DNA structure (specific)
A
- a condensation reaction between two nucleotides forms a phosphodiester bond
- DNA molecule is a double helix with two polynucleotide chains held together by hydrogen bonds between the specific complimentary base pairs
- two hydrogen bonds form between adenine and thymine
- three hydrogen bonds form between the guanine and cytosine
8
Q
What is a genome?
A
- the complete set of genes in a cell
9
Q
What is a proteome?
A
- the full range of proteins that a cell is able to produce
10
Q
What is a locus?
A
- a gene occupies a fixed position, which is called a locus
11
Q
Genetic codes (i.e. triplets)
A
- a sequence of three DNA bases, called a triplet, codes for a specific amino acid
- the genetic code is universal, so certain bases always code for the same amino acid
- it is non-overlapping, so the distinction is clear
- it is degenerate, so multiple codons can code for the same amino acid during protein synthesis
12
Q
Exons
A
- the sequence which code for amino acid sequences
13
Q
Introns
A
- non-coding sequences which separate exons
14
Q
DNA replication - what, when and why?
A
- before a cell divides in mitosis or meiosis, it must replicate its DNA
- occurs during the S phase of the cell cycle to prepare for meiosis or mitosis
- this is to ensure all daughters cells have the genetic information they need
15
Q
DNA replication - the process
A
- DNA helicase, an enzyme, breaks the hydrogen bond which link the base pairs of DNA.
- Therefore, the double helix then separates into two separate strands and unwinds, which produces a replication fork
- Each of the exposed polynucleotide strands acts as a template, which free nucleotides can bind to by complementary base pairing.
- The free nucleotides are joined together by DNA polymerase, an enzyme, so a new polynucleotide strand is formed on each of the two original strands of DNA (through the formation of phosphodiester bonds)
- This forms two new DNA molecules.
- Each of the new DNA molecules contains one of the original DNA strands and one of the new strands.
- As half of the original DNA is conserved, it is coined semi-conservative.
16
Q
Who put forward evidence for semi-conservative replication?
A
- put forward by Watson and Crick
- Meselson and Stahl validated the theory
17
Q
What is the evidence of DNA replication?
A
18
Q
RNA types
A
- messenger RNA (mRNA) - carries out the actions of genes
- transfer RNA (tRNA) - carries amino acids around during translation
- ribosomal RNA (rRNA) - put amino acids together in chains
19
Q
mRNA
A
- carries genetic messages from DNA in the nucleus to the ribosomes where proteins are synthesised
- the molecule is unfolded and varies in length and base sequence
20
Q
tRNA
A
- they collect a specific amino acid and take it to the ribosome for assembly into proteins
- it is a small molecule with some base pairing that allows it to form a “clover leaf” shape
- one end of the tRNA molecule carries a specific amino acid, while the other end has an anticodon
- anticodon- a triplet of bases which determines the amino acid carried
21
Q
Transcription - the foundations
A
- DNA helicase unwinds the DNA helix by breaking the H bond between the complementary base pairs
- RNA polymerase attaches to the DNA template—the sense strand
- RNA polymerase moves along the sense strand, it attaches free RNA nucleotides by forming phosphodiester bonds
- This is continued until the end of the chain is reached
22
Q
Transcription - the result
A
- Pre-mRNA is formed (in eukaryotes, but mRNA in prokaryotes)
- This pre-mRNA contains introns, but these need to removed so a functional protein is produced
- The introns are removed by pre-mRNA splicing, and the exons join together
- After splicing has occurred, the mRNA leaves the nucleus via the nuclear pores of the nuclear envelope
- The mRNA travels to the ribosome, where the DNA helix rewinds itself
23
Q
Translation
A
- The ribosome binds to the mRNA at a start codon
- A tRNA with a complementary anticodon binds to the start codon and is held in place by the ribosome
- The ribosome slides along the mRNA to read the next codon
- A new tRNA binds to the second codon, bringing with a second specific amino acid/ complementary anticodon
- The two amino acids are now close enough for a peptide bond to form between them
- The first tRNA is now released and leaves its amino acid behind
- The ribosome again slides along the mRNA to read the next codon
- This process continues until the stop codon is reached, which signal the ribosome that the polypeptide is complete, so the ribosome releases it
- Finally, the polypeptide goes through folding, in order to form, secondary and tertiary structures. It may also be joined to other polypeptide chains to make quaternary structures.
- The tRNA molecules are recycled and ribosome reused.
- mRNA may be used again if the gene expression is high, but if not, it is degraded
