Genetic Code + DNA Flashcards
What is a gene?
A sequence of mononucleotide bases on a DNA molecule coding for a sequence of amino acids in a polypeptide chain which produces a protein that results in a characteristic
What is the genome?
All the genes in an organism/species
What is the proteome?
Full range of proteins that a cell can make
What do chromosomes in cells carry? 2
- A large amount of DNA
- Numerous genes
What is genetic code?
The sequence of base triplets [codes] in DNA/mRNA coding for specific amino acids
What is a codon?
A base triplet coding for an amino acid
4 words to describe genetic code
- Universal
- Degenerate
- Non overlapping
- Triplet code
Why is genetic code non overlapping?
Each triplet code is adjacent and seperate, doesn’t share bases
Why is genetic code degenerate?
- More possible combinations of triplets than amino acids
- Some amino acids code for more than 1 triplet
Why is genetic code universal?
- It is the same genetic code in all living organisms, codes for the same proteins
What are start and stop codons?
Codons telling cell when to start and stop gene production
Where are start and stop codons found?
At the beginning and the end of the gene
What is a mononucleotide?
A monomer that makes up polynucleotides e.g DNA and RNA
What bonds to what in DNA?
Phosphate to pentose to nitrogen containing base
What are mononucleotides made up of?
- Phosphate group
- Pentose sugar
- Nitrogen containing base
What are mononucleotides joined by?
Condensation reactions
What is the full name of DNA?
Deoxyribosenucleic Acid
What is the function of DNA?
To store genetic code which contains instructions for coding for the characteristics of an organism
What does DNA control?
Manufacture of proteins
What bases does DNA have?
- Adenine
- Thymine
- Cytosine
- Guanine
What type of sugar is in RNA nucleotides?
Ribose
What is DNA made up of?
Long polynucleotides
What is RNA made up of?
Short polynucleotides
What is different about RNA bases compared to DNA bases?
Uracil replaces thymine as a base
What is the full name of RNA?
Ribonucleic acid
What is the main function of RNA?
To transfer genetic information from the DNA in the nucleus to the ribosomes in the cytoplasm
Where do polynucleotides bond?
Between the phosphate group of 1 mononucleotide and the sugar group of another
What is the by product of condensation reactions?
Water
What type of bond forms between mononucleotides?
Phosphodiester
How many polynucleotide strands make up DNA?
2 - double stranded
How many polynucleotide strands make up RNA?
1 - single stranded
How are the 2 polynucleotide strands in DNA joined?
Hydrogen bonds between bases
Why are the 2 strands of DNA described as “antiparallel”?
They run in opposite directions
Why do 2 DNA strands run in opposite directions? 2
- The hydrophilic phosphate groups are outside the molecule
- The hydrophobic bases lie within the molecule
What is complimentary base pairing?
Each base can only join with one specific partner
How do DNA bases join up?
Adenine to Thymine
Cytosine to Guanine
How many hydrogen bonds form between A and T?
2
How many hydrogen bonds form between C and G?
3
How do the 2 antiparallel strands form a double helix?
They twist
Why did scientists doubt DNA could carry genetic code?
It had a relatively simple chemical composition
What did other scientists argue must carry genetic info and why?
Proteins - more chemically varied
Define codon
Triplet of bases coding for a specific amino acid
Define “gene mutation”
Changes to the base sequence of DNA during DNA replication
List the types of gene mutation 5
- Insertion
- Deletion
- Substitution
- Inversion
- Duplication
What is substitution?
When one base is swapped for another
What is deletion and how is it a mutation?
- One base is removed
- Causes a frame shift
- Changes all following codons
What is insertion?
An extra base is added
What is duplication?
One/more bases is repeated
What is inversion?
Sequence of bases is reversed
What are the 3 theories of DNA replication?
- Fragmentation
- Semi conservative replication
- Conservative replication
Explain the theory of fragmentation in DNA replication
Parent DNA breaks into segments and new nucleotides fill the gaps randomly
Explain the theory of semi conservative DNA replication 3
- Parent DNA molecule separated into 2 strands
- Each strand becomes a template for formation of complementary strand
- 2 new daughter DNA molecules: 1/2 parent DNA 1/2 new DNA from nucleotides
Explain the theory of conservative DNA replication 2
- Parent DNA molecule acts as template for new daughter molecule assembled from free nucleotides
- Parent DNA is unchanged
Explain how Meselson and Stahl proved semi conservative replication - 7
- Bacteria [E.coli] grown in medium of heavy 15n isotope
- All bacterial DNA contains heavy nitrogen
- Then fed on medium containing light 14n isotope
- Allowed to replicate a few times
- Bacterial DNA is extracted and centrifuged
- Shows up in centrifuge tube as a band in the middle of the tube as DNA is half heavy and half light
- After replicating twice, one intermediate band in the middle and one light band at the top
- Some of the DNA is 1/2 heavy, 1/2 light and some is all light
Explain DNA replication - 7
- DNA helicase unwinds DNA
- By breaking hydrogen bonds between complementary bases
- Forms 2 single strands - each original strand acts as template strand
- New DNA nucleotides pair with complementary bases on template strand
- DNA polymerase joins nucleotides together in condensation reaction by forming hydrogen bonds between the bases
- There are now 4 DNA strands which wind back up to form 4 DNA helixes
How is DNA antiparallel and why?
- Nucleotides arranged oppositely
- DNA polyermase is an enzyme whose active site only binds to nucleotides at 1 end
How is DNA replication semi conservative?
Each new DNA molecule has one strand of original DNA and one stand of new nucleotides
