Genetic code/Cell function - finished Flashcards
(52 cards)
Structure of DNA
- Double Helix
- Polynucleotide
- Anti Parallel strands
- Hydrogen bonds between complementary base pairs
What are the functions of DNA?
Genetic code
Replication of DNA
What is the genetic code?
The base sequence along the DNA molecule carries information required to put amino acids in order, to make polypeptides.
Why is the replication of DNA important?
DNA needs to be copied! otherwise daughter cells wont have sufficient DNA to synthesise proteins
What is a gene?
Section of DNA that codes for a polypeptide
What is an allele?
Varient of a gene
What is semi conservative replication?
Using one strand of DNA as a template to make a second strand
What happens during DNA replication?
1- Enzymes unwind the2 DNA strands by breaking the H bonds between the base pairs
2 -The exposed bases attract free complimentary neucleotides
3 - An enzyme works its way along joining all of the nueclotides together forming a poly nucleotide
4 - Because the 2 DNA strands are anti parallel the enzyme cant build both strands completely at the same time. The second strand loops around on itself and creates little bursts of DNA that are then joined together later
5 - Enzyme then winds the DNA back together
What enzyme is responsible for unwinding the DNA?
Helicase
What enzyme joins the nucleotides together to form a polynucleotide?
DNA Polymerase
What enzyme joins the littl bursts of polynucleotides together on the second strand?
DNA ligase
What are the corresponding base pairs?
Adenine - Thymine
Cytocine - Guanine
What experiment should be used as evidence for semi conservative replication?
Messelsohn and Stahl
What organism did Messelsohn and Stahl use and why?
Used E.coli (bacterium)
- has DNA (ring form)
- They copy DNA every 20 minutes when their cells divide
What did Messelsohn and Stahl do in their experiment?
Grew E.coli on agar which conained N15 (heavy N isotope) so that all DNA in the bacteria cells should have nitrogenous bases made using N15
They transferred the e.coli from N15 agar onto N14 agar
Evergy generation they removed some E.coli
And examined the DNa by puttting it in a centrafuge and separating it out.
What did Messelsohn and Stahl find out?
Gen 0 = 1 molecule of DNA N15/N15
Gen 1 = 2 molecules of DNA N15/N14
Gen 2 = 2 molecules of DNA N15/N14 and 2 molecules N14/N14
Gen 3 = 2 molecules of DNA N15/N14 and 6 molecules of N14/N14
What assumption does Messelsohn and Stahl make?
That the cell uses N15 in the same way it uses N14
What is Meiosis?
A type of cell division
“reduction devision”
What is meiosis used for?
producing Haploid cells
Production of Gametes
How many division cycles are there in Meiosis?
Meiosis 1
Meiosis 2
What is the first stage before meiosis even happens?
Interphase Replication of DNA REplication of organelles Protein Synthesis (produces spindle fibres) ATP production
What are the stages in Meiosis 1?
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1 (SOMETIMES)
What happens in prophase 1?
Nuclear membrane breaks down
Spindle forms at the poles of the cells
Chromosomes condense and join together in homologous pairs called bivalent pairs
Bivalent chromosomes are connected at points called Chiasmata
What happens in Metaphase 1?
Chromosome pairs line up at either side of the equator
Centromeres are one either side of the equator - NOT on the equator
Chiasmata still in place
