Topic 2.7: DNA Replication, Transcription & Translation Flashcards Preview

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Flashcards in Topic 2.7: DNA Replication, Transcription & Translation Deck (31)
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1

DNA is semiconservative

1) One strand is from an original template molecule and one strand is newly synthesised
2) Each base only pairs with its complementary partner and ensures the sequence is conserved

2

Meselson-Stahl thesis

Supported the theory that DNA replication occurred via a semi-conservative process

3

Models for DNA Replication (3)

1) Conservative Model
2) Semi-Conservative Model
3) Dispersive Model

4

Dispersive Model

New molecules are made of segments of new and old DNA

5

Conservative Model

An entirely new molecule is synthesised from a DNA template (which remains unaltered)

6

Semi-Conservative Model

Each new molecule consists of one newly synthesised strand and one template strand

7

Meselson-Stahl experiment (2)

They incorporated radioactive nitrogen isotopes into
DNA
• Templates were prepared with heavier 15N
• New sequences were replicated with lighter 14N

8

Meselson-Stahl results (2)

The DNA was then separated via centrifugation to determine its composition of radioisotopes
• 1st division: DNA had 15N and 14N (i.e. mixed)
• 2nd division: DNA is mixed or has 14N only

9

DNA Replication Enzymes (2)

1) Helicase
2) DNA Polymerase III

10

Helicase (2)

1) Unwinds and separates the double stranded DNA
2) Breaks the hydrogen bonds between the base pairs

11

DNA Polymerase III

1) Free nucleotides line up opposite complementary partners
2) DNA Pol III covalently joins the free nucleotides together

12

DNA replication

Semi-conservative process whereby pre-existing strands act as templates for newly synthesised str

13

Polymerase Chain Reaction (PCR)

Artificial method of DNA replication that is used to rapidly copy a specific sequence.

14

PCR Steps in a Thermal Cycler

Denaturation (90°)
Annealing (55°)
Elongation (75°)

15

Denaturation

DNA is heated to separate the two strands

16

Annealing

Primers attach to ends of a target sequence

17

Elongation

A heat-tolerant polymerase copies strands (Taq polymerase)

18

30 Cycles in PCR = ? copies

2^30 copies of the target DNA sequence

19

Transcription

Synthesis of an RNA sequence from a DNA template

20

RNA Polymerase

1) Separates the DNA strands (breaks H bonds between base pairs)
2) Covalently joins free complementary RNA nucleotides together

21

Types of RNA

1) mRNA – Transcript used to make protein
2) tRNA – Transfers amino acid to ribosome
3) rRNA – Catalytic component of ribosome

22

Genetic code

Set of rules by which information encoded in mRNA sequences is converted into a polypeptide sequence

23

Codons

Triplets of bases which correspond to a particular amino acid

24

Order of codons

Codons determines the amino acid sequence for a protein

25

Start codon

AUG

26

STOP codons (3)

UAA
UAG
UGA

27

Features of the Genetic Code (2)

1) Universality – All organisms use the same genetic code
2) Degeneracy – Multiple codons may code for the same amino acid

28

Translation

Process of protein synthesis in which the genetic information encoded in mRNA is translated into a sequence of amino acids on a polypeptide chain

29

Steps of translation (Mr Cat App)

1) Messenger RNA (goes to…)
2) Ribosome (reads sequence in …)
3) Codons (recognised by …)
4) Anticodons (found on …)
5) Transfer RNA (which carries …)
6) Amino acids (which join via …)
7) Peptide bonds (to form …)
8) Polypeptides

30

Gene

Sequence of DNA that is transcribed into RNA