Genetic code/Cell function - finished Flashcards
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
What happens in Anaphase 1?
Bivalent is pulled apart
Whole chromosome is pulled to the pole
Chiasmata break and fragments of chromosomes may be pulled to the opposite pole as a piece of its homologous partner
What are the main ways of ensuring genetic variablity?
Chiasmata
Independant assortment
Random Fertilisation
Mutation
What is a Chiasmata?
The “crossing over” of genes between 2 chromosomes in a bivalent pair. Allows the mixing of genetic materials
What is independent assortment?
Random segregation
Parental chromosomes from parents are pulled appart at random creating genetic variablity
What happens when chromosomes arent separated properly at anaphase?
non-disfunction
What happens in telophase 1?
In plants - DOESNT HAPPEN
In animals - 2 seperate nuclei reform/ chromosomes become invisible?
Why doesn’t interphase happen a second time?
No replication of DNA is needed
When does Cytokenesis 1 happen?
Can only happen after Telophase 1
What are the conditions of Prophase 2?
Only happens on animals if cytokenesis and telophase 1 happen (if they dont happen prophase canont happen as there is no membrane to break down)
What happens in meiosis 2?
Meiosis 2 is effectively the same as mitosis.
Takes place at 90degrees to meiosis 1 in the cell
In animals - 1 spindle per cell
In plants - 2 spindles per cell
What are the 4 ways of creating genetic variation?
Chiasmata
Independant assortment
Randon fertilization
Mutation
Why is mutation different to the other ways of creating genetic variation?
Because it is the only one that interoduces new genes.
What is chiasmata?
Bivalent chromosomes are connected at points called chiasmata.
Allows “crossing over” of genes - mixing a genetic materials between the two chromosomes.
What is independant assortment?
Random segregation
Parental chromosomes from parents are pulled appart at random creating genetic variability
If chromosomes arent separated properly at anaphase = non dysfunction
What are the 2 different types of protein?
Structural - Collagen
Functional - Enzymes/ Haemogobin
How many amino acids are there?
22
What are triplets?
Groups of 3 nitrogenous bases that cde for different amino acids
What is meant by a degenerate amino acid?
An amino acid that is only coded for by a single triplet
What is a stop code?
a triplet that does not code for amino acids.
What are the 2 stages of protein synthesis?
Transcription “copying”
Translation
What is transcription?
Nucleic acid base sequence of dna is copied into messenger RNA
Where is messenger RNA produced and where does it work?
Produced in the nucleus
Used in the ribosomes
How does transcription happen?
DNA strand with required gene is split “unravelled” by enzymes to expose the bases.
Attraction of complimentary RIBONUCLEOTIDES (uracil not thymine)
RNA polymerase moves down the ribonucloetides joining them together
Polymerised ribinucleotides move out of the way to allow more copies.
Enzymes zip DNA back up
mRMA moves out of the nucleus through the nuclear pores to the ribosomes
What is a non coding and coding strand of DNA?
Coding strand - Useful strand that codes for amino acids.
Non coding strand - Non useful strand - used to make copies of the coding strand.
What is translation?
Turns the base sequences of mRNa into amino acid sequence in a polypeptide. - Happens in ribosomes
How does translation happen?
mRNA strand positions itself at the juction of the 2 subunits that make up the ribosome
The codons at the junction attract tRNA molecules whihc bear complimentary anti-codons
Each tRNA molecule carries with it a specific amino acid molecule.
THe two amina acids join together (condensation reaction) under the influence of enzymes in the ribosomes.
The 1st tRNA molecule breaks off ad goes into the cytoplams to pick up another amino acid.
The ribosomes slides down the mRNA molecule one codon
Cycle repeats until it reaches a stop codon. No tRNA molecule so no amino acid brought in.
What is a codon?
3 bases of mRNA
What is an anti codon?
3 bases of tRNA
