Nucleotides and nucleic acids Flashcards
Describe the structure of a nucleotide?
- phosphate group
- pentose sugar
- ribose base
Name the pentose sugars in DNA and RNA?
DNA = deoxyribose
RNA = ribose
What is the difference between ribose and deoxyribose?
Ribose has a hydroxyl (OH) group at position 2 whereas deoxyribose has a hydrogen atom (H) there
How are polynucleotide strands formed and broken down?
- formed through condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone)
- broken down by hydrolysis reactions using a molecule of water
Describe the structure of DNA?
- 2 deoxyribose polynucleic strands arranged in a double helix with 2 sugar-phosphate backbones
- H bonds form between complementary base pairings on the strands (AT,GC)
Name the purine bases and describe there structure?
- adenine and guanine
- 2 ring structures
Name the pyrimidine bases and describe there structure?
- thymine, cytosine and uracil
- 1 ring structures
Name the complementary base pairs in DNA and RNA and describe there hydrogen bonding?
DNA - 2 H bonds between adenine and thymine
RNA - 2 hydrogen bonds between adenine and uracil
Both - 3 hydrogen bonds between guanine and cytosine
Why is DNA replication semi conservative?
- strands from original DNA molecule act as a template
- new DNA molecules contain 1 old strand and one new strand
- specific base pairing enables genetic material to be conserved accurately
Explain the role of DNA helicase in semiconservative DNA replication?
Breaks H bonds between complementary base pairs to form 2 single strands which can act as templates
How is a new strand formed by semiconservative DNA replication?
- free nucleotides attach to exposed bases by complementary base pairing
- DNA polymerase joins adjacent nucleotides on new strands in a 5’ to 3’ direction via condensation reactions to form phosphodiester bonds
- H bonds reform
Identify the features of the genetic code?
- non-overlapping (each triplet is only read once)
- degenerate (more than one triplet codes for the same amino acids)
- universal (same bases and sequences used by all species)
How does a gene determine the sequence of amino acids in a protein?
consists of base triplets that code for a specific amino acid
What does transcription produce and where does it occur?
- produces mRNA
- occurs in the nucleus
Outline the process of DNA transcription?
- RNA polymerase binds to promoter region on a gene
- section of DNA uncoils into 2 strands with exposed bases, antisense strand acts as a template
- free nucleotides are attracted to their complementary bases
- RNA polymerase joins adjacent nucleotides to form phosphodiester bonds
What’s the difference between the sense and antisense strand?
Sense strand = provides the code to make a protein when read in the right direction
Antisense strand = non-coding strand that serves as a template for RNA synthesis
What happens after a strand of mRNA is transcribed?
- RNA polymerase detaches at a terminator region
- H bonds reform and DNA rewinds
- splicing removes introns from pre-mRNA in eukaryotic cells
- mRNA moves out of the nucleus via nuclear pores and attaches to ribosomes
What are introns and exons?
introns = intervening non-coding regions of a gene
exons = coding regions of a gene
What does translation produce and where does it occur?
- produces proteins
- occurs in cytoplasm on ribosomes (made of protein and rRNA)
Outline the process of translation?
- ribosomes move along the mRNA until “start” codon
- tRNA anticodons attach to complementary bases on mRNA
- condensation reactions between amino acids on tRNA form peptide bonds (requiring energy from ATP hydrolysis)
- process continues to form polypeptide chains until “stop” codon is reached
What is mRNA?
mRNA = (messenger RNA) is a single strand of RNA made from a DNA template that carries a genetic sequence to the ribosomes that read by a ribosome in the process of synthesizing a protein
What is tRNA?
tRNA = (transfer RNA) is a small RNA molecule that helps decode a mRNA sequence into a protein
What is rRNA?
rRNA = (ribosomal RNA) is a part of the ribosome that reads the order of amino acids and builds proteins through protein synthesis
Describe the structure of ATP and ADP?
Both = nucleotide derivatives of adenine
ATP = has three inorganic phosphate groups
ADP = has 2 inorganic phosphate groups
What is a mutation?
An alteration to the DNA base sequence often arising spontaneously during DNA replication
