D1 Continuity and change molecules

Question 1

DNA synthesis is…

Answer 1

the synthesis of new strands with the exact same base sequence

Question 2

In multicellular organisms, cell division is a part of THREE processes:

Answer 2

1. Growth, 2. Replacement of damaged tissues, 3. Reproduction

Question 3

What does the semi-conservative replication of DNA entail?

Answer 3

Separation of parent DNA molecule into two single strands (breaking hydrogen bond), single strands are a template for assembly of new polymer of nucleotides

Question 4

Why are the new strands of DNA that are produced by semi-conservative replication identical to the parent DNA?

Answer 4

Due to complementary base pairing - Adenine and Thymine, Cytosine and Guanine

Question 5

What are the two enzymes in charge of separation of DNA strands and linking nucleotides together for a new strand?

Answer 5

Helicase (replication fork - unwinds the double helix and breaks hydrogen bonds) and DNA polymerase (links nucleotides together for new strands)

Question 6

What is PCR and what is it used for

Answer 6

PCR (polymerase chain reaction) is used for copying DNA artificially, used for multiplying small amounts of DNA

Question 7

What is gel electrophoresis

Answer 7

A method of separating DNA based on the size of the molecules (small move faster) – allows patterns to be compared

Question 8

What can PCR and gel electrophoresis be used for

Answer 8

Forensic investigations, paternity tests

Question 9

What happens in transcription

Answer 9

A strand of DNA molecule is used by RNA polymerase as a template for synthesising a molecule of RNA – usually only one gene is transcribed

Question 10

Stages of transcription

Answer 10

1. RNA polymerase separates DNA strands into singles (only one turn of helix at a time), 2. RNA polymerase pairs up RNA nucleotides to DNA nucleotides on the strand, 3. Covalent bonds between RNA nucleotides to form one strand, 4. RNA strand leaves DNA strand, 5. DNA strands unite

Question 11

Which one of the DNA base pairs does the RNA strand not contain?

Answer 11

Thymine, replaced by Uracil to pair with Adenine

Question 12

Why is conservation and stability an important part of DNA templates?

Answer 12

They may be transcribed multiple times during the life of a cell and mutations need to be kept to a minimum, to maintain function

Question 13

Expression of genes are controlled by which processes?

Answer 13

Transcription (which can be switched off and on in the case of a gene) and translation

Question 14

What is translation?

Answer 14

Synthesis of a polypeptide, whose amino acid sequence is determined by the base sequence of the RNA molecule

Question 15

Where and how does the translation happen?

Answer 15

Ribosomes: mRNA binds on ribosome, tRNA has triplet of bases (ANTICODON) and carries matching amino acids to the anticodon, two tRNA bind simultaneously in ribosome, amino acids bond by peptide linkage - chain of three is formed –> eventually polypeptide

Question 16

Mutations altering protein structure

Answer 16

As small as one base change changes one codon and can cause radical changes to protein structure (like chains of haemoglobin causing sickle cells instead of red blood cells) or there is no effect

Question 17

What are gene mutations

Answer 17

permanent structural changes to the DNA of a gene, inheritable due to replication of the base sequence

Question 18

Three main types of gene mutations:

Answer 18

1. insertions (extra nucleotides asserted), 2. deletions (nucleotides deleted) (both affect one or more nucleotides), 3. substitutions (single base is replaced)

Question 19

Categories of base substitutions in gene mutations

Answer 19

neutral (no effects), deleterious (causing harm – most harmful ones are lethal), beneficial (useful)

Question 20

What is single nucleotide polymorphism (SNP)

Answer 20

base substitution spreads by inheritance until 1% or more of population has it (only possible with neutral or beneficial)

Question 21

When do most mutations occur

Answer 21

during DNA replication (base errors)

Question 22

What are mutagens (2 types)?

Answer 22

Agents that increase the likelihood of mutations: 1. chemical mutagens (chemical changes in DNA, e.g. nitrosamines in cigarettes or mustard gas), 2. high energy radiation (breaks bonds in DNA, e.g. x-rays)

Question 23

Mutations in somatic vs. germ cells

Answer 23

Somatic: can’t be inherited, can cause cancer to individual, germ: gamete or can turn into gamete so inheritance is possible

Question 24

Why are gene mutations good

Answer 24

variation required by natural selection, species can evolve to new conditions