key info 2 for exams

Question 1

Key events in transcription:
and diagram

Answer 1

https://cognitoedu.org/coursesubtopic/b3-alevel-aqa_sEoImuSp
-RNA polymerase enzyme binds to DNA.

• hydrogen bonds between the DNA bases break, and the two strands of the double helix separate.

-The antisense strand acts as the template for mRNA synthesis.

-Free RNA nucleotides align with the DNA template through complementary base pairing.

-In the RNA molecule, uracil pairs with adenine from the DNA strand, while adenine from the RNA molecule pairs with thymine, and cytosine pairs with guanine.

-RNA polymerase catalyses the formation of phosphodiester bonds between adjacent RNA nucleotides.

• A complementary mRNA strand is formed, carrying the same base sequence as the DNA sense strand.

-The process ends when RNA polymerase reaches a stop codon, detaches from DNA and terminates transcription.

-mRNA is released, detaches from DNA, and DNA rewinds into its double helix structure.

Question 2

what type of organisms’ (eukaryotes or prokaryotes) mRNA undergoes splicing? and what is splicing

Answer 2

In eukaryotes, pre-mRNA is spliced after transcription to remove introns(non coding bases) before it is transported to the cytoplasm but splicing doesn’t occur in prokaryotes.

Question 3

The process of natural selection includes these key steps:

Answer 3

1. There is variation in characteristics within a species.
2. More genetic variation emerges within a population due to random mutations.
3. Individuals with alleles that code for traits that are advantageous for survival are more likely to reproduce.
   4.These advantageous alleles are passed down to offspring.
   5.Over time, these beneficial alleles become more common in the population.

Question 4

antibiotic resistance stages:

Answer 4

1.Some bacteria develop random mutations that provide resistance to antibiotics.
2.When antibiotics are used, only the resistant bacteria survive, while the others die off.
3.The resistant bacteria reproduce, passing on resistant alleles to their offspring.
4.Over time, the proportion of resistant alleles increases, leading to mostly resistant bacteria.

Question 5

disadvantages of antibiotic resistance on society (3)

Answer 5

This resistance complicates treatment options, increases healthcare costs, and raises mortality rates in humans.

Question 6

Natural selection is

Answer 6

an ongoing process that enables organisms to adapt to environmental changes.

Question 7

sterile means…

Answer 7

infertile

Question 8

relate the stucture of DNA to its function (7)

Answer 8

• sugar-phosphate backbone & many H-bonds provide stability
• long molecule stores lots of information
• helix is compact for storage in nucleus ( like when you scrunch a helical spring together it becomes more compact)
• base sequence of triplets codes for amino acids
• double-stranded for semi-conservative replication
• complementary base pairing for accurate replication
• weak H-bonds break so strands separate for replication