unit 1.5 - DNA (replication, nucleotides) Flashcards
Why are strawberries good for extracting DNA?
- 8 different genomes
- Pectinase + cellulase enzymes which break down the cell wall for release of DNA
What are Nucleotides made up of?
3 main components that combine by condensation reactions
- Phosphate group
- Pentose sugar
- Organic base that contains carbon
Describe ATP
A nucleotide
Major energy currency in cells
Energy source in all living organisms/cells
What is phosphorylation?
Introducing a phosphate group into a molecule or compound
e.g adding a phosphate group to ADP (adenosine diphosphate)
How is ATP formed?
By phosphorylation
What is an exergonic reaction?
A reaction that RELEASES energy
What is an endergonic reaction?
A reaction where energy is NEEDED (taking in energy)
Where in the cell is ATP produced?
Cytoplasm, mitochondria, chloroplasts
Name 4 uses of ATP
DNA synthesis from nucleotides
Active transport
Muscle contraction (movement)
Secretion
What are the two types of nucleus acids?
Deoxyribonucleic acid - DNA
Ribonucleic acid - RNA
What pentose sugar + bases do DNA nucleotides have?
Deoxyribose
Adenine, thymine, cytosine, guanine
What pentose sugar + bases do RNA nucleotides have?
Ribose
Adenine, uracil, cytosine, guanine
Describe the structure of DNA [4]
- Double stranded polymer of nucleotides (polynucleotide)
- The alternating phosphate groups and pentose sugars form the backbone
- The polynucleotide chains are antiparallel to each other
- Molecule is twisted to form a double helix. This helix is maintained by hydrogen bonding
Where is DNA found?
In the nucleus of eukaryotic cells
What are the 2 functions of DNA?
Replication and protein synthesis
Describe the structure of RNA
- Single stranded polypeptide
- Much shorter than DNA
When is DNA copied?
During replication in the interphase
How does DNA replication occur?
- Hydrogen bonds holding the base pairs break and 2 halves of the DNA molecule separate
- DNA unwinds
- As DNA strands separate the enzyme DNA polymerase catalyses the free nucleotides to the exposed bases
- This process results in the formation of 2 identical DNA molecules - each made up of one newly synthesized chains and one from the original molecule
What is the hypothesis of the Meselson + Stahl experiment?
Semi-conservative
- Each DNA strand acts as a template for new DNA
- Each strand of DNA formed is composed of an original strand and a newly synthesized strand
Describe how the Meselson + Stahl experiment works
- The scientists extracted the bacterial DNA and centrifuged it.
- The DNA settled at a low point in the tube bc it contained the heavy N^15 isotope.
- The bacteria were washed, then transferred to a medium containing the normal lighter isotope N^14 and were allowed to replicate once.
- When extracts of DNA from the first generation culture were centrifuged it was shown to have a mid point density; half the strand was made up of N^15 DNA and the other half was made up of the new N^14 DNA
- When extracts of DNA were taken from the second generation grown in a N^14 medium, the DNA settled at mid points and high points in the tube after centifugation.
- This provided evidence which supported the semi conservative hypothesis.
Describe transcription
- DNA unwinds and unzips at a particular region to be copied; enzyme helicase catalyses the DNA
- Enzyme RNA polymerase attaches to DNA at the beginning of the sequence to be copied.
- Only one of the DNA stands acts as a template (antisense strand)
- RNA polymerase moves along the DNA forming bonds that add nucleotides one at a time to the RNA
- This results in the synthesis of a molecule of mRNA alongside the unzipped portion of DNA
- Behind the RNA polymerase the DNA stands re join to reform the double helix
- The mRNA carries the DNA code out of the nucleus through a nuclear pore to the cytoplasm and attaches to a ribosome for translation.
When does transcription occur?
When the free RNA nucleotides align themselves opposite complimentary nucleotides on the DNA stand
Describe translation
- Ribosome acts as framework moving along the mRNA, reading the code.
- mRNA contains triplet codes or codons. Each codon codes for a different amino acid.
- tRNA molecules attach to specific amino acid molecules and carry them to mRNA molecules
- Complimentary anticodon - codon bases align and are held together by the ribosome at an attachment site; a codon - anticodon complex is formed.
- Peptide bonds are formed between adjacent amino acids by condensation reaction.
Name 3 variables of the Meselson + Stahl experiment
- Temperature
- Time
- Rate of spin
Name 2 enzymes known to be involved in DNA replication and their functions
- DNA polymerase - joins nucleotides to the ends of the new DNA stand
- DNA helicase - unwinds DNA and breaks hydrogen bonds between nucleotides
