Module 2 - Nucleotides and nucleic acids Flashcards
Give two examples of nucleic acids
RNA and DNA
What three components make up a nucleotide?
- a phosphate group
- a pentose sugar
- an organic base
What purines are found in DNA and RNA?
adenine and guanine
What pyrimidines are found in DNA?
cytosine and thymine
What pyrimidines are found in RNA?
cytosine and uracil
What is the difference between purines and pyrimidines?
purines are two carbon rings whilst pyrimidines are one carbon ring
What type of nucleotides are RNA and DNA?
polynucleotide
What is the structure of RNA?
- single-stranded and short
- sugar involved is ribose
- base is ACGU
What are the three types of RNA?
- messenger RNA - mRNA
- tranfser RNA - tRNA
- ribosomal RNA - rRNA
What is mRNA?
- carries the code held in the genes to the ribosomes where the code is used to make proteins
What is tRNA?
- transports amino acids to the ribosomes
What is rRNA?
- makes up the ribosome
What does C bond to in DNA, what type of bond, and how many bonds?
Guanine, 3 hydrogen bonds
What does A bond to in DNA, what type of bond, and how many?
Thymine, 2 hydrogen bonds
Describe the structure of the DNA strands
- antiparallel meaning they lie in opposite directions
- the two strands combine and twist to make a double helix
Explain how the nucleotides in a DNA molecule are arranged as two polynucleotide strands.
- 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
What are ATP and ADP?
- phosphorylated nucleotides
What do ATP and ADP contain?
- pentose sugar
- nitrogenous base
- two or three inorganic phosphates
How is ATP produced?
- ADP is phosphorylated to form ATP
- it is made during respiration from ADP through the addition of a phosphate inorganic ion and ADP synthase
What are the properties of ATP?
- 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
What is complimentary base pairing?
- base A pairs with T through 2 hydrogen bonds
- base C pairs with G through 3 hydrogen bonds
What does semi-conservative replication mean?
- half of the original molecule is conserved in each of the new molecules
Explain semi-conservative replication.
- 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.
Why is the precise replication of DNA essential?
- to ensure that identical copies of the gene are included in every cell of the body
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
What is the genetic code?
- the order of bases on DNA
What is an allele?
- a version of a gene
What is every three bases on a gene known as?
- a codon
What is a gene?
- a sequence of codons that code for a specific protein
What are the three features of codons?
- non-overlapping
- degenerate
- universal
What does non-overlapping mean?
- each codon only codes for its specific amino acid
What does degenerate mean?
- more than one triplet can code for a particular amino acid
What does universal mean?
- there are the same 64 codons in every organism
What are the coding sequences in DNA?
- regions of the DNA that code for a particular protein
What are the non-coding sequences in DNA?
-regions of the DNA that do not code for anything
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
Why is DNA replication important?
- cell division for growth and repair
- produces replicated DNA for cell division
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
What is transcription of a gene?
- the DNA sequence in a gene is transcribed onto mRNA
Where does transcription occur?
- in the nucleus
Why is gene transcription used in eukaryotes?
- because the full chromosomal DNA molecules is too large to leave the nucleus via a nuclear pore.
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
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
What is the first stage of protein synthesis and what does it include?
- transcription and it involves the production of a mRNA strand
What is included in protein synthesis?
- transcription and translation of genes
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
What direction does DNA polymerase only synthesize?
- from the 3’ end to the 5’ end of the DNA strand
