Chapter 6 Nucleic acid and Protein synthesis Flashcards
(19 cards)
Structure of nucleotides
- a nitrogen-containing base
- a pentose sugar
- a phosphate group
Structure of ATP
Adenosine triphosphate
- a ribose
- 3 phosphate groups
- an adenine
Purines and Pyrimidines
PURINES: double ring structure. Adenine and Guanine
PYRIMIDINES: single ring structure. Cytosine, Thymine and Uracil
Structure of DNA molecule
- double helix structure
- two antiparallel polynucleotide strands lying side by side. 3’ to 5’ direction and other 5’ to 3’ direction
- has 4 nitrogenous bases: adenine, thymine, guanine, cytosine
- held together by hydrogen bonds: A-T forms 2 hydrogen bonds, G-C forms 3
- sugar-phosphate bonds make up a phosphodiester backbone which supports the DNA shape
Semi-conservative replication of DNA during S-phase
DNA replication is described as semi-conservative because each DNA molecule is made up of one old, conserved strand of DNA and one new one
- DNA helicase unzips the stands, resulting in the formation of a replication fork
- Separated strands each providing a template for creating a new strand of DNA
- DNA primase makes a small piece of RNA called a primer, this marks the starting point for the construction of the new strand of DNA
- DNA polymerase binds to the primer and makes the new strand of DNA
- Bases are added from the 5’ end to the 3’ end, leading strand
- Lagging strand, made in a series of small chunks called Okazaki fragments. Each fragment is started with an RNA primer, DNA polymerase then adds a short row of DNA bases in the 5’ to 3’ direction
- Once the new DNA has been made, enzyme exonuclease removes all the RNA primers from both strands of DNA. Polymerase fills in the gaps left behind
- DNA ligase seals up the fragments of DNA in both stands to form a continuous double-strand
Different types of RNA
- mRNA: messenger RNA, carries the genetic information in the form of a template from the nucleus to the ribosome from translation
- tRNA: transfer RNA, has a specific amino acid at one end and an anticodon at the other end. It fits onto the mRNA at ribosomes at the complementary mRNA codon for protein synthesis
Structure of RNA
- single strand
- a pentose sugar
- 4 nitrogenous bases: adenine, uracil, guanine, cytosine
Define gene
A length of DNA which codes for a specific polypeptide or amino acid chain
Define codon
Sequence of three nucleotide bases which codes for a specific amino acid
Features of the genetic code
- a three-letter code
- universal
- has punctuations
- described as redundant or degenerate
Define transcription
Copying the genetic information in a molecule of DNA into a complementary strand of mRNA
Define translation
Sequence of nucleotide in a molecule of mRNA is converted into a corresponding sequence of amino acid in a polypeptide chain
How is the primary transcript modified before translation?
The pre.mRNA contains introns and extrons. The introns are spliced and removed, and the extrons are joined together to form a continuous strand called mature mRNA
Process of protein synthesis
- DNA unwinds at the gene to be transcribed
- RNA polymerase binds to the promoter region of the gene
- RNA polymerase moves along the template strand, building a complementary mRNA strand
- When RNA polymerase reaches a stop signal, transcription ends
- mRNA leaves the nucleus via the nuclear pore
- mRNA binds to a ribosome
- tRNA molecules bring amino acids to the ribosome
- Each tRNA has an anticodon that matches a codon on the mRNA
- The ribosome moves along the mRNA, reading codons three bases at a time
- Peptide bonds join amino acids to form a polypeptide chain
- This continues until a stop codon is reached
- The completed polypeptide leaves the ribosome and folds up into its secondary and tertiary structure
Modifying the mRNA
In eukaryotes, the RNA molecule formed following transcription is modified by the removal of non-coding sequences (introns) and the joining together of coding sequences (exons) to form mRNA
Define frame-shift mutation
A type of gene mutation caused by the insertion or deletion of one or more nucleotides, resulting in an incorrect reading of the sequence of triplets in the genetic code due to a shift in reading frame
Substitution mutation
A base is replaced by a different base
Deletion mutation
A base is lost and not replaced
Insertion mutation
A base is added
