Studied by 4 people
red blood cell
What is the structure of a nucleotide?
pentose sugar , phosphate group, nitrogenous base
Name the pentose sugars in DNA & RNA.
DNA: deoxyribose
RNA: ribose
Describe how polynucleotide strands are formed and broken down.
Condensation reactions between nucleotides form strong phosphodiester bonds (sugar-phosphate backbone).
Hydrolysis reactions use a molecule of water to break these bonds.
Enzymes catalyse these reactions
Describe the structure of DNA.
Molecule twists to form double helix of 2 deoxyribose polynucleotide strands (so there are 2 sugar-phosphate backbones).
H-bonds form between complementary base pairs (AT & GC) on strands that run antiparallel
Name the purine bases and describe their structure
adenine C5H5N5
guanine C5H5N5O
two-ring molecules
Name the pyrimidine bases
cytosine
thymine
uracil
Name the complementary base pairs in DNA AND MORE
2 H-bonds between adenine (A) + thymine (T)
3 H-bonds between guanine (G) + cytosine (C)
Name the complementary base pairs in RNA
2 H-bonds between adenine (A) + uracil (U)
3 H-bonds between guanine (G) + cytosine (C)
Why is DNA replication described as semiconservative?
Strands from original DNA molecule act as templates.
New DNA molecule contains 1 old strand & 1 new strand
Explain the role of DNA helicase in semiconservative replication.
Breaks H-bonds between base pairs to form 2 single strands, each of which can act as a template
How is a new strand formed during semiconservative replication?
Free nucleotides attach to exposed bases by complementary base pairing.
DNA polymerase joins adjacent nucleotides on new strand in a 5' → 3' direction via condensation reactions to form phosphodiester bonds.
H-bonds reform
Identify features of the genetic code
Non-overlapping= each triplet is only read once.
Degenerate= more than one triplet codes for the same amino acid (64 possible triplets for 20 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 acids.
What does transcription produce and where does it occur?
produces mRNA
occurs in nucleus
What happens after a strand of mRNA is transcribed?
RNA polymerase detaches at terminator region.
H-bonds reform & DNA rewinds
splicing removes introns from pre-mRNA in eukaryotic cells.
mRNA moves out of nucleus via nuclear pore & attaches to ribosome
What does translation produce and where does it occur?
Produces proteins
Occurs in cytoplasm on ribosomes (which are made of protein + rRNA)
Describe the structure of adenosine triphosphate (ATP)
- nucleotide derivative of adenine
- has a pentose sugar (Ribose)
- has a nitrogenous base ( adenine)
- has 3 inorganic phosphate groups
Describe the structure of adenosine diphosphate (ADP).
- nucleotide derivative of adenine
- has a pentose sugar (Ribose)
- has a nitrogenous base ( adenine)
- has 2 inorganic phosphate groups
What is a mutation?
An alteration to the DNA base sequence.
Mutations often arise spontaneously during DNA replication
What bond is formed between nucleotides?
phosphodiester bond
What is mRNA?
messenger RNA
carries the copy of the gene out of the nucleus and transfers it to the ribosomes where the code is for protein synthesis
What is tRNA?
- transfer RNA
- found in the cytoplasm
- has an amino acid binding site at one end and an anticodon at the other
- transfers amino acids to ribosomes
What is rRNA?
ribosomal RNA
makes up the ribosomes
DNA
A complex molecule containing the genetic information that makes up the chromosomes.
RNA
A single-stranded nucleic acid that passes along genetic messages.
Purines
Nitrogenous bases that have a double ring of carbon and nitrogen atoms
- adenine and guanine.
Pyrimidines
Nitrogenous bases that have a single ring of carbon and nitrogen atoms
- cytosine and thymine (Uracil)
ADP
Adenosine diphosphate; a molecule that ATP becomes when it gives up one of its three phosphate groups.
ATP
Adenosine triphosphate; the main energy source that cells use for most of their work.
Polynucleotide
A polymer consisting of many nucleotide monomers in a chain; nucleotides can be those of DNA or RNA.
Phosphodiester bond
- the type of bond that links the nucleotides in DNA or RNA.
- joins the phosphate group of one nucleotide to the hydroxyl group on the sugar of another nucleotide
DNA helicase
- Breaks the hydrogen bonds between the two polynucleotide DNA strands.
- Unzips the double helix to form 2 single strands during DNA replication
Gene
A segment of DNA on a chromosome that codes for a specific trait
Triplet
The three nucleotides of DNA which code for one amino acid.
Codon
A specific sequence of three adjacent bases on a strand of DNA or RNA that provides genetic code information for a particular amino acid
Anticodon
group of three bases on a tRNA molecule that are complementary to an mRNA codon
Stop codon
codon that signals to ribosomes to stop translation
DNA polymerase
An enzyme that catalyses the formation of phosphodiester bonds between nucleotides during the synthesis of a new DNA strand.
Exons
sections of DNA that code for amino acid sequences.
RNA polymerase
An enzyme that catalyses the formation of phosphodiester bonds between nucleotides during the synthesis of a new RNA strand.
DNA topoisomerase
An enzyme that unwinds and winds coils of DNA that form during replication and transcription.
DNA primase
places a primer to tell DNA polymerase to stop working
DNA ligase
an enzyme that eventually joins the sugar-phosphate backbones of the Okazaki fragments
enzymes needed for DNA replication
DNA topoisomerase
DNA helicase
DNA primase
DNA polymerase
DNA ligase
enzymes needed for transcription
Helicase
RNA polymerase
What causes the formation of a double helix shape in DNA?
hydrogen bonding between complementary base pairs on two antiparallel DNA polynucleotides
Which direction is the gene strand always read in?
5’ to 3’
Note 
Flashcard (21)