Module 2 - Nucleotides and nucleic acids Flashcards
(47 cards)
1
Q
Give two examples of nucleic acids
A
RNA and DNA
2
Q
What three components make up a nucleotide?
A
- a phosphate group
- a pentose sugar
- an organic base
3
Q
What purines are found in DNA and RNA?
A
adenine and guanine
4
Q
What pyrimidines are found in DNA?
A
cytosine and thymine
5
Q
What pyrimidines are found in RNA?
A
cytosine and uracil
6
Q
What is the difference between purines and pyrimidines?
A
purines are two carbon rings whilst pyrimidines are one carbon ring
7
Q
What type of nucleotides are RNA and DNA?
A
polynucleotide
8
Q
What is the structure of RNA?
A
- single-stranded and short
- sugar involved is ribose
- base is ACGU
9
Q
What are the three types of RNA?
A
- messenger RNA - mRNA
- tranfser RNA - tRNA
- ribosomal RNA - rRNA
10
Q
What is mRNA?
A
- carries the code held in the genes to the ribosomes where the code is used to make proteins
11
Q
What is tRNA?
A
- transports amino acids to the ribosomes
12
Q
What is rRNA?
A
- makes up the ribosome
13
Q
What does C bond to in DNA, what type of bond, and how many bonds?
A
Guanine, 3 hydrogen bonds
14
Q
What does A bond to in DNA, what type of bond, and how many?
A
Thymine, 2 hydrogen bonds
15
Q
Describe the structure of the DNA strands
A
- antiparallel meaning they lie in opposite directions
- the two strands combine and twist to make a double helix
16
Q
Explain how the nucleotides in a DNA molecule are arranged as two polynucleotide strands.
A
- adjacent nucleotides binding together via a condensation reaction to form phosphodiester bonds
- this creates a sugar-phosphate backbone between the sugar of one molecule and the phosphate group of another
- hydrogen bonds are between complementary base pairings.
- polynucleotides are antiparallel
17
Q
What are ATP and ADP?
A
- phosphorylated nucleotides
18
Q
What do ATP and ADP contain?
A
- pentose sugar
- nitrogenous base
- two or three inorganic phosphates
19
Q
How is ATP produced?
A
- ADP is phosphorylated to form ATP
- it is made during respiration from ADP through the addition of a phosphate inorganic ion and ADP synthase
20
Q
What are the properties of ATP?
A
- small - moves easily in and out of the cells
- soluble - most processes happen in aqueous environments
- intermediate amounts of energy released - enough but not too much to be wasted as thermal energy
- easily regenerated - renewable energy source
21
Q
What is complimentary base pairing?
A
- base A pairs with T through 2 hydrogen bonds
- base C pairs with G through 3 hydrogen bonds
22
Q
What does semi-conservative replication mean?
A
- half of the original molecule is conserved in each of the new molecules
23
Q
Explain semi-conservative replication.
A
- DNA unwinds its double helix through the enzyme DNA gyrase
- DNA helicase breaks the hydrogen bonds between the CBP
- both original strands of DNA act as a template for free-floating DNA nucleotides (within nucleus) to CBP with the bases on the template strands
- DNA polymerase catalyses the formation of the sugar-phosphate backbone by catalysing the formation of phosphodiester bonds formed in condensation reactions between adjacent nucleotides.
24
Q
Why is the precise replication of DNA essential?
A
- to ensure that identical copies of the gene are included in every cell of the body
25
How does DNA fit inside the nucleus?
- it wraps around histone proteins as DNA is negatively charged due to phosphate groups and histone is positively charged
- these form a structure called nucleosomes
- these form long chains of chromatins which are wound up to produce a single chromosome
26
What is the genetic code?
- the order of bases on DNA
27
What is an allele?
- a version of a gene
28
What is every three bases on a gene known as?
- a codon
29
What is a gene?
- a sequence of codons that code for a specific protein
30
What are the three features of codons?
- non-overlapping
- degenerate
- universal
31
What does non-overlapping mean?
- each codon only codes for its specific amino acid
32
What does degenerate mean?
- more than one triplet can code for a particular amino acid
33
What does universal mean?
- there are the same 64 codons in every organism
34
What are the coding sequences in DNA?
- regions of the DNA that code for a particular protein
35
What are the non-coding sequences in DNA?
-regions of the DNA that do not code for anything
36
What is discontinuous replication?
- DNA polymerase can only synthesize the sugar-phosphate backbone in the 5' - 3' direction
- due to the strands being antiparallel, only one strand will be synthesized as it is in this orientation
- this is called the leading template and is synthesized continuously
- the lagging template will have to be synthesized discontinuously
- DNA polymerase synthesised short fragments of the strand called Okazaki fragments
- these are then joined together by DNA ligase
37
Why is DNA replication important?
- cell division for growth and repair
- produces replicated DNA for cell division
38
How does the DNA molecule unwind?
- DNA Helicase travels along the DNA backbone, catalysing reactions that break the hydrogen bonds between complementary base pairs as it reaches them
39
What is transcription of a gene?
- the DNA sequence in a gene is transcribed onto mRNA
40
Where does transcription occur?
- in the nucleus
41
Why is gene transcription used in eukaryotes?
- because the full chromosomal DNA molecules is too large to leave the nucleus via a nuclear pore.
42
Explain the process of gene transcription
- RNA polymerase attaches to DNA
- DNA uncoils, breaking hydrogen bonds between CBP
- one of these strands is used as a template to make mRNA
- RNA polymerase then lines up free RNA nucleotides along the template strand and they undergo CBP
- this means the mRNA strand is a copy of the DNA template strand
- once they have paired up, adjacent nucleotides are joined together by RNA polymerase, catalyzing the formation of phosphodiester bonds and forming a mRNA strand
- RNA polymerase then moves down the DNA strand
- hydrogen bonds between uncoiled strands of DNA reform once RNA polymerase passes and the strands coil back to a double helix
- once RNA polymerase reaches a stop codon, it detaches from the DNA
-mRNA moves out through a nuclear pore then attaches to a ribosome
43
Explain the process of protein translation
- mRNA attaches to a ribosome and tRNA carries amino acids to the ribosome
- tRNA attaches to a mRNA strand through CBP as it contains anticodons complimentary to mRNA codons
- a second tRNA molecule attaches itself to mRNA in the same way
- rRNA catalyses the formation of a peptide bond between the two amino acids attached to the tRNA molecules
- this joins the amino acids together
- 1st tRNA molecule moves away, leaving its amino acid behind.
- 3rd molecule binds to the next codon, binding its amino acid to the 2nd tRNA
- this cycle repeats until a stop codon is reached on the mRNA molecule
- a polypeptide chain is produced and it moves away from the ribosome
44
What is the first stage of protein synthesis and what does it include?
- transcription and it involves the production of a mRNA strand
45
What is included in protein synthesis?
- transcription and translation of genes
46
What is the second stage of protein synthesis and what does it include?
- translation and it involves the production of a polypeptide chain by joining amino acids by ribosomes based on the order of codons in mRNA
47
What direction does DNA polymerase only synthesize?
- from the 3' end to the 5' end of the DNA strand
