!!!⭐️Genetic info, variation and relationships: Genes, DNA and Protein Synthesis (good for genes and proteins OP4103)

Question 1

What are the character of prokaryotic DNA?

Answer 1

Short
Circular
Have no histones present (naked)

Question 2

Give a piece of evidence that supports the endosybiotic theory

Answer 2

The circular naked loops of DNA that are found in mitochondria and chloroplasts

Question 3

Give some characteristics of eukaryotic DNA

Answer 3

• molecules are long
• linear
• associated with histone proteins

Question 4

What does each nucleosome consist of?

Answer 4

A cluster of 8 histone proteins around which DNA is wrapped twice

Question 5

Give the three steps to how a DNA and its associated protein form a chromosome:

Answer 5

1. The DNA double helix wraps around histone proteins forming the nucleosome
2. The DNA histone complex coils further and is then wrapped to form the chromosome
3. Once the chromosome is visible, the DNA and protein is describes as condensed chromatin

Question 6

What is the locus of a DNA molecule?

Answer 6

The specific position of each gene

Question 7

How many chromosomes do humans have?

Answer 7

46

Question 8

What are homologous pairs?

Answer 8

Pairs of chromosomes where one is the maternal chromosome and the other is the paternal chromosome. They carry the same genes but not necessarily the same alleles

Question 9

What happens to the homologous pairs in meiosis?

Answer 9

They separate to produce gametes that are haploid

Question 10

What’s an allele and how do they arise?

Answer 10

It’s one of the different variations of a gene as they each have a slightly different sequence of bases brought upon by mutations

Question 11

How can mutations have a negative impact on the organism?

Answer 11

Because the changes in the base sequence will mean a different sequence of amino acids are coded for so a different polypeptide and hence a different protein is produced which may not function e.g. if it’s an enzyme and has a different shape it may not fit the substrate and can’t function hence causing consequences for the organism

Question 12

What do genes of the same species have in common?

Answer 12

They are found on the same locus of the same chromosome

Question 13

What is a gene?

Answer 13

A base sequence of DNA that contains the coded information for making polypeptides and functional RNA

Question 14

What is a genome?

Answer 14

The complete set of genes in cells/ all of the DNA of an organism

Question 15

The gene is a base sequence of DNA that codes for…

Answer 15

-the amino acid sequence of a polypeptide

Question 16

What’s a proteome?

Answer 16

The full range of proteins produced by the genome

Question 17

Describe and explain three features of the genetic code

Answer 17

• its universal as most of the time each triplet codes for the same amino acid in all organisms which is indirect evidence for evolution and this allows for genetic engineering
• its non overlapping as each base in the sequence is read only once and there are no overlaps between codons
• its degenerate; you can have more than one codon for each amino acid

Question 18

How does a sequence of three DNA bases code for a specific amino acid?

Answer 18

• As a few amino acids are coded for by only a single triplet and the remaining amino acids are coded for by between two and six triplets each
• a triplet is always read in one particular direction along a strand

Question 19

What does an RNA nucleotide consist of?

Answer 19

• a phosphate group
• a ribose sugar
• one of the bases A, U, C or G

Question 20

Give the three types of RNA

Answer 20

• Ribosomal RNA (rRNA)
• messenger RNA (mRNA)
• transfer RNA (tRNA)

Question 21

Give four features of mRNA’s structure

Answer 21

• long stranded
• single helix
• made of a linear sequence of triplet codons

Question 22

What is mRNA used for?

Answer 22

It acts as a templete for protein synthesis

Question 23

How is mRNA’s structure adapted to its function?

Answer 23

Its information is stored in a linear sequence of triplet codons and the sequence of the codons determines the amino acid sequence of a specific polypeptide that’ll be made

Question 24

What is ribosomal RNA?

Answer 24

A long , single stranded molecule that forms part of the structure of ribosomes

Question 25

Give 5 features of tRNA

Answer 25

- small molecule - its single stranded and folded into a clover leaf - each tRNA is specific to one amino acid - its anti codon region forms complementary base pairs with a codon of the mRNA strand - It contains complementary base pairs within the molecule

Question 26

What are the three ways complementary base pairs are important in RNA?

Answer 26

- in determining the structure of tRNA and hence the anticodon and which amino acid it’s specific to - codon, anti codon interactions - transcription of DNA to mRNA

Question 27

Compare the location of DNA, mRNA and tRNA

Answer 27

DNA is mostly found in the nucleus mRNA is manufactured in the nucleus but found throughout the cell and tRNA is also manufactured in the nucleus and found throughout the cell

Question 28

Compare the size of DNA, mRNA and tRNA

Answer 28

DNA is the largest molecule, then mRNA then tRNA being the smallest

Question 29

Compare the quantity of DNA, mRNA and tRNA

Answer 29

DNAs quantity is mostly constant for all cells of a species except gametes while mRNA and tRNA quantities vary from cells and with levels of metabolic activity

Question 30

Compare the stability of DNA, mRNA and tRNA

Answer 30

DNA is very chemically stable, mRNA is less stable than tRNA or DNA as individual molecules are usually broken down in cells within a few days, and tRNA is more chemically stable than mRNA but less than DNA

Question 31

What are introns?

Answer 31

Non-coding regions on pre-mRNA that need to be removed

Question 31

What are exons?

Answer 31

Coding sequences of pre-mRNA that need to be attached together

Question 31

How is prokaryotic transcription different to eukaryotic transcription?

Answer 31

In prokaryotes, there’s no splicing of the mRNA and the transcription and translation stages are coupled

Question 32

Why is the proteome much bigger than the genome?

Answer 32

Because one gene can lead to the production of many proteins in alternative splicing

Question 33

What are the steps of eukaryotic transcription?

Answer 33

1. RNA polymerase binds to the region of DNA to be transcribed 2. The two strands here unwind and separate breaking the H bonds between complementary base pairs leaving both strands of the DNA molecule in the region of the gene exposed 3. One strand acts as a template strand to make mRNA 4. Activated RNA nucleotides in the nucleus are attracted to their complementary bases and H bond with their corresponding DNA nucleotides (A on DNA pairs with U on RNA) 5. RNA nucleotides align themselves along the DNA template strand as RNA polymerase moves along the template strand to form phosphodiester bonds between the adjacent RNA nucleotides 6. RNA reaches a specific termination sequence and it detaches and the process stops 7. The pre-mRNA has now been produced as the sequence of bases on the DNA molecule have been transcribed to a sequence of codons on the mRNA molecule 8. Introns are then removed through splicing and the exons join together resulting in the mature mRNA molecule which leaves the nucleus via nuclear pore

Question 34

Give the steps of translation

Answer 34

1. A ribosome attaches to the starting codon at one end of the mRNA molecule 2. The tRNA molecule with the complementary anti-codon sequence moves to the ribosome and pairs up with the codon on the mRNA and this tRNA carries a specific amino acid 3. The t RNA molecule with a complementary anticodon pairs up with the next codon on the m RNA and this t RNA molecule carries another amino acid 4. The ribosome moves along the m RNA bringing together two tRNA molecules at any one time each pairing up with the corresponding two codons on the mRNA. 5. The two amino acids on the tRNA are joined by a peptide bond using an enzyme and ATP which is hydrolysed to provide the required energy 6. The ribosome moves on to the third codon in the sequence on the mRNA and so linking the amino acids on the second and third tRNA molecules 7. As this happens, the first tRNA is released from its amino acid and is free to collect another amino acid 8. The process continues with up to 15 amino acids added each second 9. Once the ribosome reaches a stop codon, the polypeptide chain is complete

Question 35

What determines the order that tRNA molecules line up in translation?

Answer 35

The sequence of codons on mRNA which is determined by the DNA sequence of triplets that make up a gene

Question 36

What happens to the polypeptide chain after translation?

Answer 36

1. It’s coiled or folded to produce the secondary structure 2. The secondary structure is folded to produce the tertiary structure 3. Different polypeptide chains and non protein groups are linked to form the quaternary structure