TOpic 6 Flashcards
Describe the structure of a nucleotide [3]
Main central structure is a pentagon
on the top left corner there is a phosphate group
and on the right top corner ther’s a nitrogenous base
Name the pentose sugars in RNA and DNA [2]
- Deoxyribose in DNA
- Ribose in RNA
Describe the structure of DNA [4]
- Double stranded polymer of nucleotides twisted to form a double helix
- joined by phosphodiester bonds
- Hydrogen bonds form between complementary base pairs, A and T, C and G
- Antiparallel strands
Name the purine bases [2]
Adenine and Guanine
Describe the structure of the purine bases
two ring molecules
Name the pyrimidine bases [3]
Thymine, Cytosine and Uracil
What is complementary base pairing? [3]
- Describe how hydrogen bonds form between complementary purine and pyrimidine bases
- Two bonds form between A and T (or U)
- Three bonds form between G and C
Why is DNA replication described as semiconservative? [3]
- Strands from original DNA molecule act as templates
- New DNA molecule contains 1 old strand and 1 new strand
- Specific base pairing enables genetic material to be conserved accurately
How is a new strand formed during semiconservative replication? [3]
- Free nucleotides from nuclear sap attach to exposed bases via complementary base pairing
- DNA polymerase joins adjacent nucleotides on a new strand in a 5’ to 3’ direction via condensation reactions to form phosphodiester bonds
- Hydrogen bonds form between complementary base pairs
Outline the role of DNA ligase in DNA replication [3]
- As DNA replicates in an antiparallel fashion, the leading strand (5’ 3’) is replicated continuously whereas the lagging end (3’ 5’) is replicated discontinuously
- Short nucleotide sequences are formed
- DNA ligase catalyses the formation of phosphodiester bonds between the nucleotide sequences
Describe the structure of RNA [3]
- Single stranded polymer of nucleotides
- nucleotides joined by phosphodiester bonds
- hydrogen bonds form between complementary base pairs (A and U) and (C and G)
What is the function of mRNA?
Carries genetic information from the nucleus to the ribosomes for protein synthesis
How do genes determine the structure of proteins? [4]
- DNA base triplets code for amino acids
- Triplet sequence determines amino acid sequence
- Sequence of amino acids determines proteins’s primary structure
- Protein primary structure determines where bonds form when folding into tertiary structure
What is a mutation? [3]
- A random alteration to the DNA base sequence, altering the order of coded amino acids
- This may result in a change in protein structure.
- Mutations often arise spontaneously during DNA replication
What are the three types of gene mutation? [3]
- Substitution
- Insertion
- Deletion
What are the consequences of substitution mutations [3]
- Silent mutation (no consequence) as DNA is degenerate
- Mutation may alter the amino acid coded for. This can alter the structure of the polypeptide causing it to no longer function
- Mutation may lead to the production of a stop codon. The length of the polypeptide chain is shorter
What are the consequences of insertion/deletion mutations?
Produce a frameshift, altering each subsequent codon and rendering the protein non functional
Describe the structure of tRNA [5]
- Single strand of 80 nucleotides
- Folded into clover shape
- Anticodon on one end, amino acid binding site on the other
- Anticodon binds to complementary mRNA codon
- Amino acids corresponds to anticodon
What do transcription and translation produce and where do they occur? [2]
- Transcription produces mRNA, occurs in nucleus
- Translation produces proteins, occurs in the cytoplasm in ribosomes
Outline the process of transcription [5]
- DNA Helicase unwinds section of dna, breaking hydrogen bonds between the DNA strands. Antisense strands acts as a template
- RNA polymerase binds to promoter region on a gene
- Free RNA nucleotides align next next to their complementary bases
- RNA polymerase joins adjacent RNA nucleotides, forming phosphodiester bonds.
- RNA polymerase reaches stop codon and detaches. mRNA complete
Define exon
Regions of DNA or RNA that code for amino acid sequences
define intron
Non coding sequences of DNA found between exons
What happens after a strand of mRNA is transcribed? [4]
- RNA polymerase detaches at terminator region
- Hydrogen bonds reform and DNA rewinds
- Splicing removes introns from pre-mRNA in eukaryotic cells, leaving only exons
- mRNA moves out of nucleus via nuclear pore and attaches to ribosome
Outline the process of translation [5]
- mRNA attaches to groove between subunits of ribosome
- Ribosome moves along mRNA until start codon is reached
- Amino acid-tRNA complex anticodon attaches to complementary mRNA codon via hydrogen bonding. Another complex binds.
- Peptide bond forms between adjacent amino acids in the complexes
- Ribosome moves along one codon and release empty tRNA. Process continues to form polypeptide chain until stop codon is reached
Describe the structure of the pyrimidine bases
Single ring structure
Define anticodon
A sequence of three nucleotide bases at one end of a tRNA molecule that is specific to an mRNA codon
What are the types of bonding between base pairs in RNA and DNA? [2]
Phosphodiester bonds in DNA
Hydrogen bonds in RNA
What’s the role of tRNA? (4)
- attaches to a specific amino acid
-transports amino acid to ribosomes - helps form primary structure of protein
- anticodon identifies specific amino acid
