Chapter 16: Molecular Genetics Flashcards
What is DNA?
A molecule that carried genetic information
What is DNA made up of?
Nucleotides
What are nucleotides made of?
1) A deoxyribose molecule (sugar)
2) A phosphate group
3) A nitrogen-containing base
What are the four types of nitrogen bases?
Adenine (A), Thymine (T), Guanine (G), Cytosine (C)
How does the numbering system work in the nucleotide?
The 1’ carbon is bonded to the nitrogen base, the 3’ carbon is bonded to the OH group, and the 5’ carbon is bonded to the phosphate group. The numbers always follow the cloclwise direction.
How are the nucleotides bonded together?
The 5’ carbon of the most bottom nucleotide bonds to the phosphate group, which bonds to the 3’ carbon of another nucleotide. The 5’ carbon from that nucleotide then bonds to another phosphate group.
What are the directions of the anti-parallel nucleotide strands, and how can their directions be observed?
The complementary strand runs in the opposite direction of the nucleotide strand. From bottom to top, the nucleotide strand runs in the 3’ to 5’ direction, while the complementary strand runs in the 5’ to 3’ direction
What nitrogen bases pair together?
Adenine (A) and Thymine (T); 2 bonds, Cytosine (C) and Guanine (G); 3 bonds
What are the bonds between nitrogen base pairs?
Hydrogen bonds
What structure do the two anti-parallel strands form?
A double helix structure
What is a gene?
A segment of DNA
What determines the polypeptides formed in a gene?
The nucleotide sequence
What does a codon do?
Codes for one amino acid
What are codons made of?
Three nucleotides (consecutive base sequences)
What is a gene mutation?
A change in the nucleotide sequence of a gene
What can gene mutation cause?
May lead to a change in the protein product of a gene, whch may lead to an observable phenotype
What were the three types of DNA replication models (including the two incorrect replication models), and what do they predict?
Conservative: The two parent strands rejoin after duplication, to form one new and one old strand
Semiconservative: Each daughter strand contains one old strand belonging to the parent, and one new duplicated strand
Dispersive: Each strand is a mix of old and new strands
Which DNA replication model is accurate?
Semiconservative
How does base pairing aid in DNA replication?
Serves as a template for a new strand
How is DNA replication coordinated?
Via a large team of enzymes
What are the steps in DNA replication?
1) DNA replication starts at the origin of replication
2) DNA replication expands sideways
3) Continues until the replication bubbles come into contact with one another, in which case DNA replication is complete
What does topoisomerases do?
Unwind DNA to reduce torsional stress in DNA molecule during DNA replication
What does helicase do?
Seperates double strand DNA into single strands (breaks the hydrogen bonds linking nitrogen base pairings using ATP)
What does single strand binding proteins (SSBP) do?
Prevents the single stranded DNA to anneal (join) back together into double stranded DNA
What does RNA primase do?
Makes a short RNA primer, which is the building block for DNA replication
What does DNA polymerase do?
Polymerises free deoxyribonucleotides (a nucleotide that contains deoxyribose) into a newly synthesised DNA strand (5’ to 3’) by reading a single strand of DNA (3’ to 5’) as a template. It also replaces RNA primer with DNA
What does ligase do?
Joins DNA fragments together
What are the 3 types of RNA?
Messanger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
Acronym: MRT
What are mRNA used for?
Transcription and translation from genes to proteins
What are rRNA?
Components of ribosomes in translation of mRNA
What does tRNA do?
Attatches to amino acids and is used in translation of mRNA
What does the DNA genotype do?
Determines traits (phenotypes) through expression of genes and protein synthesis
What is transcription?
The synthesis of RNA under the direction of DNA in the nucleus
What is translation?
The synthesis of proteins under the direction of RNA in the cytoplasm
What is the source and product of information translatation?
Information in codons is translated into amino acids
What is some information about genetic code?
- Nearly universal (common to almost all organisms on Earth)
- Amino acids may be coded by more than one codon, but each codon only codes for one amino acid
- Without punctuation and is uninterrupted
How is RNA molecules transcribed from DNA templates?
By a process similar to DNA replication
What does RNA polymerase do?
Carries out transcription (Like DNA replication but for RNA)
What is the DNA template also known as?
Antisense DNA
How is the starting and ending of transcription marked?
By specific sequences of nucleotides
What nucleotide sequence indicates the start of transcribing?
Promoter
What are the 3 stages of transcription?
1) Initiation
2) Elongation
3) Termination
What happens at initiation during transcription?
RNA polymerase attatches to promoter
What happens at elongation during transcription?
RNA nucleotides form the mRNA strand
What happens at termination during transcription?
Enzymes reach the ending sequence and detatch from the DNA template (antisense DNA)
Where does the detatched mRNA move to?
The cytoplasm out of the nuclear pores
What does translating of DNA mean?
Converts DNA code (in codons) into protein code (amino acids sequence)
How are tRNAs differentiated?
By a special 3 nucleotide sequence on the tRNA called the anticodon. Anticodons are complimentary to the codons on mRNA that the amino acid is associated with
What are the 2 stages of translation?
1) Initiation
2) Elongation
What happens at initiation in translation?
The mRNA binds to the ribosomes, and the start signal codon binds with tRNA which holds the anticodon UAC
What happens at elongation in translation?
tRNA with the complimentary anticodon to the codon on the mRNA binds within the ribosomes. A new amino acid is joined to the already existing chain with a peptide bond, and the tRNA of the previous codon (with a different anticodon) is released from the ribosomes. Ribosomes (with current tRNA still attatched) move on to the next codon
What are some differences between DNA and RNA?
Sugar unit: deoxyribose vs ribose
Nitrogen-containing bases: thymine (T) vs uracil (U)
Ratio of nitrogen-containing bases: 1:1 vs no fixed ratio
Molecule type: large and insoluble vs small and soluble
Lifespan: permenant molecule in the nucleus vs temporary molecule which is made when needed
What is a gene vector?
A DNA molecule that is used as a vehicle to artificially carry foreign genetic material into another cell
What is a plasmid?
A small circular DNA obtained from bacteria that can be used to transfer genes (a type of vector)
What is recombinant DNA?
A vector containing foreign DNA
What is a transgenic organism?
An organism whose genetic material has been altered
What is the 4-step process in genetic modification?
1) Human chromosome containing the insulin gene is obtained
2) A plasmid from the bacteria is obtained
3) The plasmid is mixed with the DNA fragment
4) The bacterium takes up the plasmid
How is the human chromosome containing insulin and the plasmid from the bacteria obtained?
Both ends of the insulin gene / plasmid is cut from the human chromosome / bacteria using a restriction enzyme. This enzyme produces sticky ends at the ends of the gene, which can pair with complementary bases to form a double strand
How does bacteria take up the plasmid?
Via heat or electric shock, which opens up the pores on the cell surface membrane
How is the plasmid mixed with the DNA gene?
DNA ligase is added to join the insulin gene to the plasmid
