dna Flashcards
DNA
Holds genetic information which codes for polypeptides (proteins)
DEOXYRIBOSE
THYMINE
RNA
Transfers genetic information from DNA to ribosomes
RIBOSE
URACIL
Describe how nucleotides join together to form polynucleotides
● Condensation reactions, removing water molecules
● Between phosphate group of one nucleotide and deoxyribose / ribose of another
● Forming phosphodiester bonds
Describe the structure of DNA
● Polymer of nucleotides
● Each nucleotide formed from
deoxyribose, a phosphate group and a nitrogen-containing organic base
● Phosphodiester bonds join adjacent nucleotides
● 2 polynucleotide chains held together by hydrogen bonds
● Between specific complementary base pairs - adenine / thymine and
cytosine / guanine
● Double helix
describe the structure of Mrna
Polymer of nucleotides
● Each nucleotide formed from ribose, a phosphate
group and a nitrogen-containing organic base
● Bases - uracil, adenine, cytosine, guanine
● Phosphodiester bonds join adjacent nucleotides
● Single helix
dna s2f
● Two strands → both can act as templates for semi-conservative replication
● Hydrogen bonds between bases are weak → strands can be separated for replication
● Complementary base pairing → accurate replication
● Many hydrogen bonds between bases → stable / strong molecule
● Double helix with sugar phosphate backbone → protects bases / hydrogen bonds
● Long molecule → store lots of genetic information (that codes for polypeptides)
● Double helix (coiled) → compact
semi conservative replication
DNA helicase breaks hydrogen bonds between complementary bases, unwinding the double helix
2. Both strands act as templates
3. Free DNA nucleotides attracted to exposed bases and join by specific complementary base pairing
4. Hydrogen bonds form between adenine-thymine and guanine-cytosine
5. DNA polymerase joins adjacent nucleotides on new strand by condensation reactions
6. Forming phosphodiester bonds
Use your knowledge of enzyme action to suggest why DNA polymerase
moves in opposite directions along DNA strands
● DNA has antiparallel strands
● So shapes / arrangements of nucleotides on two ends are different
● DNA polymerase is an enzyme with a specific shaped active site
● So can only bind to substrate with complementary shape
contrast dna in euk to dna in proks
● Eukaryotic DNA is longer
● Eukaryotic DNA is linear, prokaryotic DNA is circular
● Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not
● Eukaryotic DNA contain introns, prokaryotic DNA does not
chromosome
● Long, linear DNA + its associated histone proteins
● In the nucleus of eukaryotic cells
gene
A sequence of DNA (nucleotide) bases that codes for:
● The amino acid sequence of a polypeptide
● Or a functional RNA (eg. ribosomal RNA or tRNA)
locus
fixed position gene occupies on particular dna molecule
nature of genetic code
Triplet code A sequence of 3 DNA bases, called a triplet, codes for a specific amino acid
Universal The same base triplets code for the same amino acids in all organisms
Non-overlapping Each base is part of only one triplet so each triplet is read as a discrete unit
Degenerate An amino acid can be coded for by more than one base triplet
What are ‘non-coding base sequences’ and where are they found?
Non-coding base sequence - DNA that does not code for amino acid sequences / polypeptides:
1. Between genes - eg. non-coding multiple repeats
2. Within genes - introns
exon
Base sequence of a gene coding for amino acid sequences (in a polypeptide)
intron
Base sequence of a gene that doesn’t code for amino acids, in eukaryotic cells
transcription
Transcription Production of messenger RNA (mRNA) from DNA, in the nucleus
translation
Production of polypeptides from the sequence of codons carried by mRNA, at ribosomes
contrast the structure of tRNA and mRNA
● tRNA is folded into a ‘clover leaf shape’, whereas
mRNA is linear / straight
● tRNA has hydrogen bonds between paired bases,
mRNA doesn’t
● tRNA is a shorter, fixed length, whereas mRNA is a
longer, variable length (more nucleotides)
● tRNA has an anticodon, mRNA has codons
● tRNA has an amino acid binding site, mRNA doesn’t
transcription process
- Hydrogen bonds between DNA bases break
- Only one DNA strand acts as a template
- Free RNA nucleotides align next to their complementary bases on the template strand
○ In RNA, uracil is used in place of thymine (pairing with adenine in DNA) - RNA polymerase joins adjacent RNA nucleotides
- This forms phosphodiester bonds via condensation reactions
- Pre-mRNA is formed and this is spliced to remove introns, forming (mature) mRNA
Describe how production of messenger RNA (mRNA) in a eukaryotic cell is
different from the production of mRNA in a prokaryotic cell
● Pre-mRNA produced in eukaryotic cells whereas mRNA is produced directly in prokaryotic cells
● Because genes in prokaryotic cells don’t contain introns so no splicing in prokaryotic cells
Describe how translation leads to the production of a polypeptide
- mRNA attaches to a ribosome and the ribosome
moves to a start codon - tRNA brings a specific amino acid
- tRNA anticodon binds to complementary mRNA
codon - Ribosome moves along to next codon and another
tRNA binds so 2 amino acids can be joined by a
condensation reaction forming a peptide bond
○ Using energy from hydrolysis of ATP - tRNA released after amino acid joined polypeptide
- Ribosome moves along mRNA to form the
polypeptide, until a stop codon is reached
atp role in translation
● Hydrolysis of ATP to ADP + Pi releases energy
● So amino acids join to tRNAs and peptide bonds form between amino acids
