UNIT 4 Flashcards
Draw a labelled diagram to show four DNA nucleotides, each with a different base, linked together in two strands
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Explain the structure of the DNA double helix, including its subunits and the way in which they are bonded together.
subunits are nucleotides
one base, one deoxyribose and one phosphate in each nucleotide
description/ diagram showing base linked to deoxyribose C1 and phosphate to C5
four different bases - adenine, cytosine, guanine and thymine
nucleotides linked up with sugar-phosphate bonds
covalent/ phosphodiester bonds
two strands (of nucleotides) linked together
base to base
A to T and G to C
hydrogen bonds between bases
Describe the genetic code
composed of mRNA base triplets
called codons
64 different codons
each codes for the addition of an amino acid to a growing polypeptide chain
the genetic code is degenerate
meaning more than one codon can code for a partiuclar amino acid
the genetic code is universal
meaning it is the same in almost all organisms
(AUG is the) start codon
Explain briefly the advantages and disadvantages of the universality of the genetic code to humans
genetic material can be transferred between species/ between humans
one species could use a useful gene from another species
transgenic crop plants/ livestock can be produced
bacteria/ yeasts can be genetically engineered to make a useful product
viruses can invade cells and take over their genetic apparatus
viruses cause disease
Distinguish between RNA and DNA.
DNA is double-stranded while RNA is single-stranded;
DNA contains deoxyribose while RNA contains ribose;
the base thymine found in DNA is replaced by uracil in RNA;
Describe the roles of mRNA, tRNA and ribosomes in translation
mRNA with genetic code/ codons tRNA with anticodon tRNA with amino acid attached ribosome with two sub-units mRNA held by ribosome start codon two tRNA molecules attached with mRNA on ribosome peptide bond between amino acids on tRNA polypeptide forms continues until a stop codon is reached polypeptide is released
Outline the structure of the nucleosomes in eukaryotic chromosomes.
contain histones
eight histone molecules form a cluster in a nucleosome
DNA strand is wound around the histones
wound around twice in each nucleosome
(another) histone molecule holds the nucleosome(s) together
Compare the processes of DNA replication and transcription
both involve unwinding the helix
both involve spearating the two strands
both involve breaking hydrogen bonds between bases
both involve complementary base pairing
both involve C pairing with G
both work in a 5 --> 3 direction
both involve linking/ polymerization of nucleotides
replication with DNA nucleotides and transcritpion with RNA nucleotides
details of ribose/ deoxyribose difference
adenine pairing with uracil instead of thymine
only one strand copied not both
no ligase/ no Okazaki fragments with transcription
DNA or RNA polymerase
both require a start signal
but this signal is different for each
transcripiton has only one starting point
but replication has multiple starting points
replication gives two DNA molecules whilst transcription gives mRNA
Explain the process of DNA replication
occurs during (S phase of ) interphase/in preparation for mitosis/cell division;
DNA replication is semi-conservative;
unwinding of double helix / separation of strands by helicase (at replication origin);
hydrogen bonds between two strands are broken;
each strand of parent DNA used as template for synthesis;
synthesis continuous on leading strand but not continuous on lagging strand;
leading to formation of Okazaki fragments (on lagging strand);
synthesis occurs in 5 3direction;
Outline the structure of tRNA
tRNA is composed of one chain of (RNA) nucleotides
tRNA has a position/end/site attaching an amino acid (reject tRNA contains an amino acid)
at the 3’ terminal / consisting of CCA/ACC
tRNA has an anticodon
anticodon of three bases which are not base paired / single stranded / forming part of a loop
tRNA has double stranded sections formed by base pairing
double stranded sections can be helical
Outline the structure of tRNA
tRNA is composed of one chain of (RNA) nucleotides
tRNA has a position/end/site attaching an amino acid (reject tRNA contains an amino acid)
at the 3’ terminal / consisting of CCA/ACC
tRNA has an anticodon
anticodon of three bases which are not base paired / single stranded / forming part of a loop
tRNA has double stranded sections formed by base pairing
double stranded sections can be helical
Outline the structure of a ribosome
small subunit and large subunit;
mRNA binding site on small subunit;
three tRNA binding sites / A, P and E tRNA binding sites;
protein and RNA composition
Explain the process of translation
translation involves initiation, elongation/translocation and termination;
mRNA binds to the small sub-unit of the ribosome;
ribosome slides along mRNA to the start codon;
anticodon of tRNA pairs with codon on mRNA:
complementary base pairing (between codon and anticodon);
(anticodon of) tRNA with methionine pairs with start codon / AUG is the start codon;
second tRNA pairs with next codon;
peptide bond forms between amino acids;
ribosome moves along the mRNA by one codon;
movement in 5 to 3 direction;
compare DNA transcription with translation
both in 5 to 3 direction
both require ATP
DNA is transcribed and mRNA is translated
transcription produces RNA and translation produces polypeptides/ protein
RNA polymerase for transcription and ribosomes for translation/ ribosomes in translation only
transcription in the nucleus (of eukaryotes) and translation in the cytoplasm/ at ER
tRNA needed for translation but not transcription
