Polypeptide Synthesis

Question 1

What is the definition of a peptide

Answer 1

Two or more amino acids joined together by peptide bonds

Question 2

What is the difference between a polypeptide and a polypeptide chain

Answer 2

They refer to the same thing. Remember that only a peptide is different

Question 3

How does a polypeptide chain become a protein?

Answer 3

It detatches from the ribosome and moved to the Golgi body to be packaged

Question 4

What happens to the mRNA after it has been used to create a polypeptide chain

Answer 4

It is broken down into individual nucleotides to be reused

Question 5

What are some names for the DNA strand used

Answer 5

Sense strand, coding

Question 6

What are some names for the mRNA strand synthesised

Answer 6

Antisense strand, non-coding, template

Question 7

How is pre-mRNA processed to become mature mRNA

Answer 7

Splicing (removal of introns (non-coding) and joining of exons (coding)), addition of a 5’ cap and a poly-A tail (from the polyadenylation signal)

Question 8

How is a 5’ cap added to pre-mRNA and why

Answer 8

The 5’ cap is added to the first nucleotide in the pre-mRNA. The cap is a modified guanine nucleotide, and it protects the transcript from being broken down. It also helps the ribosome attach to the mRNA and start reading it to make a protein.

Question 9

What is the process of polyadenylation and why does it occur

Answer 9

An enzyme adds a chain of adnenine nucleotides to the mRNA (think AAAAAAA). This makes the molecule more stable and prevents its degradation)

Question 10

Where is RNA contained in eukaryotic cells?

Answer 10

mRNA - messenger RNA, nucleus and cytoplasm
tRNA - transfer RNA, cytoplasm
rRNA - ribosomal RNA, ribosomes

Question 11

What is the purpose to rRNA?

Answer 11

The ensure the alignment of mRNA and ribosomes

Question 12

Where is DNA found in prokaryotes

Answer 12

Has a nucleoid, but no nucleus and also has plasmids in the cytoplasm
A nucleoid is a non-membrane bound compact form of DNA. A plasmid is a form of extra-chromosomal DNA

Question 13

What is the structure of DNA in prokaryotes

Answer 13

Free-floating circular DNA chromosomes, not bound by proteins, unlike eukaryotic DNA which is wound around histone

Question 14

Where is DNA located in eukaryotes?

Answer 14

Found in the nucleus (nDNA) and in the mitochondria (mtDNA)

Question 15

What is the structure of DNA in eukaryotes

Answer 15

DNA is found wrapped tightly around histones, which helps the DNA condense into a small amount of space. Coiled DNA forms supercoils, which are then packaged together to form chromosomes.

Question 16

What are differences between eukaryotic and prokaryotic DNA

Answer 16

Prokaryotic is circular, free-floating and non-protein bound unlike the histones in eukaryotes. Eukaryotic DNA is linear rather than circular. The genomes are larger with long non-coding and repetitive sequences

Hence the need for splicing and checking in eukaryotes

Question 17

What are the steps in transcription

Answer 17

Transcription occurs in the nucleus, in which the RNA polymerase breaks the hydrogen bonds between the nucleotide base pairs, separating a section of the helix to be transcribed. In this process, a single mRNA strand is formed as a series of complement bases to the DNA strand being transcribed. As the pre-mRNA strand is synthesised from its 5’ end to the 3’ end, thymine is swapped for uracil. The resulting strand is terminated when the RNA polymerase reads a polyadenylation signal while transcribing, allowing an enzyme to cut the pre-mRNA strand. Pre-mRNA is processed through splicing and the addition of a 5’ cap. The strand then binds to proteins in the nuclear pore complex and is transported from the nucleus to the ribosome in the cytoplasm for translation.

Question 18

What are the steps in translation

Answer 18

In the first step of translation initiation, the mature mRNA is bound to the small subunit of the ribosome. This includes sets of codons consisting of three nucleotides corresponding to resulting amino acids. It then connects an aminoacylated tRNA to the mRNA strand in the A site of the ribosome. The ribosome’s large subunit then binds to the complex, beginning translation. In elongation, the tRNA is moved to the P site where hydrogen bonds form between the AUG codon and the amino acid. This dissociates the tRNA which is moved to the E site. Meanwhile, another amino acid-bonded tRNA molecule attaches to the A site. The process then repeats. The resulting amino acids form peptide bonds to create a polypeptide chain extending from the P site, with termination occurring when a stop codon enters the A site.

Question 19

What are the start and stop codons (examples)

Answer 19

Start - AUG, stop - UAC (examples)

Question 20

What is the importance of mRNA in polypeptide synthesis

Answer 20

The correct construction of mRNA, formed from complementary base pairs to the DNA sequence, is important to specify the correct tRNA carrying a specific amino acid to bind with the matching mRNA codon. This ensures that the right amino acids sequence of the resulting polypeptide chain and, hence, the correct protein is created.

Question 21

What is the importance of tRNA in polypeptide synthesis

Answer 21

The role of tRNA is vitally important in ensuring that its anticodon specifies and binds to the correct amino acid. This will ensure that the resulting polypeptide chain will have the right amino acid sequence that allows the protein-folding process to occur correctly. If not, the protein will not have the correct shape, a feature that is critical in determining its function.

Question 22

What is the significance of polypeptide synthesis (/producing proteins)

Answer 22

• Proteins are extremely important for cell and organism structure and function. Particularly important for multicellular organisms which require a high degree of coordination
• Polypeptide synthesis is also important for increasing the complexity of organisms. There is a large increase in the ratio of proteins to genes as organisms become more complex, since at each stage in the polypeptide synthesis process there are opportunities for variation. Segments of mRNA may be rearranged to produce different variants from a single gene, and a variety of post-translational modifications mean that polypeptides may be edited to perform different functions

Question 23

How do genes affect phenotypic expression

Answer 23

Whilst an organism’s genetic makeup will remain static throughout its life, its observable traits may change over time as a result of their environment. Our genotypes allow us to predict our phenotypes to a certain extent.

Question 24

How does environment affect phenotypic expression

Answer 24

External factors, such as the environment, have a say in how our genes are expressed. Certain genes may be switched on at different stages of development, or only expressed to certain extents (such as extreme heat or cold). A great human example is identical twins, who have the same genetic code, but who often develop different characteristics as they age. We can consider genotype as a range of phenotypic possibilities due to different environmental influences.

Question 25

What is the structure of an amino acid?

Answer 25

Amino acids are organic compounds which have a central carbon, bound to an amine group, a carboxyl group, a hydrogen, and a R-group. This R group determines the type of amino acid, and gives the molecule different properties

Question 26

How is the protein structure formed

Answer 26

Polypeptide chains fold to become proteins. This process is influenced by interactions between non-polar and polar side groups. Amino acids with non-polar side groups will be found on the inside of the protein and vice versa, hence causing the chain to be folded inwards at that point.

Question 27

What is a primary protein structure

Answer 27

A sequence of a chain of amino acids (polypeptide chain)

Question 28

What is a secondary protein structure

Answer 28

Hydrogen bonding of the peptide backbone, causing the polypeptide chain to fold (hydrophilic and hydrophobic)

Question 29

What are the 5 functions of proteins

Answer 29

Structure and storage, transport and storage, enzymes, antibodies and messengers (hormones)

Question 30

What are some examples of proteins and how does its structure link to its function

Answer 30

Haemoglobin - Transport and storage (Composed of four subunits each containing a haem group that includes an iron atom centre, Oxygen carrier, Maintains the shape of the red blood cells)
Enzymes (yk the drill, specific ones fit active sites, lock and key etc.)