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Biology 2.1.2

AS OCR biology - nucleic acids

QuestionAnswer
What are nucleotides and what are they composed of? Nucleotides are monomers of polynucleotides, consist of a phosphate, an organic nitrogenous base, & a pentose sugar (ribose or deoxyribose) joined together by covalent bonds formed in a condensation reaction. Phospho-diester bond between phosphate & sugar
What are the types of organic nitrogenous bases and what are their features? Purines - adenine, guanine - larger, double ring structure. Pyrimidines - cytosine, thymine, uracil - smaller, single ring structure.
What is the structure of DNA? Double-stranded polynucleotide made up of nucleotides containing the bases adenine, thymine, guanine, cyotsine. Sugar is deoxyribose. Antiparallel chains - 3 prime and 5 prime. Complementary base pairing. Strands twist to form a double helix.
Why are the chains in DNA always the same distance apart? Because purines bond to complementary pyrimidines - A+T, C+G, complementary base pairing
How many bonds are there between different bases? 2 H bonds between adenine and thymine, 3 H bonds between guanine and cytosine
What is a gene and what is an allele? A gene is a sequence of DNA nucleotides that codes for one or more polypeptides, and it occupies a particular locus on a chromosome. Alleles are different versions of the same gene.
What is semi-conservative DNA replication? Where 2 new DNA molecules are formed, each an exact replica of the original, and each consisting of one conserved strand and one newly-built strand
What are the steps in semi-conservative DNA replication? 1. Enzyme DNA helicase unzips DNA by breaking hydrogen bonds between bases. 2. Free DNA nucleotides in the nucleus bond to complementary exposed bases by hydrogen bonds. 3. DNA polymerase forms covalent bonds to link nucleotides and seal backbone
Which direction does the enzyme DNA polymerase work? 5' -> 3'
How is DNA adapted to its function? Large molecules can store lots of information. Stable due to double helix and hydrogen bonds minimising risk of a mutation. Hydrogen bonds allow easy unzipping for DNA replication. Sequence of coded bases act as an information store.
What is RNA? RNA is a single stranded polynucleotide made of nucleotides containing the bases adenine, uracil, guanine, cytosine, and the pentose sugar is ribose
What are the types of RNA and functions? mRNA transfers genetic information from DNA to ribosomes. rRNA is attached to protein to form ribosomes which assemble polypeptides from amino acids. tRNA is 80 nucleotides long, chain folds up, held by H bonds, carries amino acids to ribosomes
Explain the process of protein synthesis DNA helicase unzips double-stranded DNA by breaking hydrogen bonds between bases. RNA nucleotides form a molecule of mRNA that is complementary to the template DNA strand and is identical to the coding strand. The mRNA moves out of nucleus through...
Continued a nuclear pore and attaches to a ribosome on RER. tRNA bring amino acids in order according to base sequence in mRNA. Amino acids are joined by peptide bonds to form a polypeptide with a specific primary structure. Golgi -> vesicle -> out of cell
When does DNA replication occur? During the s phase of interphase in the cell cycle
Why does DNA twist into a helical shape? The base pairs aren't at right angles to the sugar-phosphate backbone so it twists into a double helix
Created by: 11043
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