D1.3

Question 1

Modifications to Polypeptides

What is initiator tRNA?

Answer 1

• A tRNA molecule with a UAC anti-codon and a methionine amino acid.
• This is the FIRT tRNA to arrive at the ribosome and triggers the start of translation at the first AUG start codon

Question 2

Modifications to Polypeptides

What is a TERNARY complex?

Answer 2

• The initator tRNA with the amino acid attached, bound to the small subunit of the ribosome.
• It binds to the 5’ end of mRNA and slides along using the UAC anticodon to scan for the first AUG starting codon.

Question 3

Modifications to Polypeptides

What is the proteome?

Answer 3

• The full set of proteins made within an organism
• Due to atlernative spilicing & different modifications - many more proteins made than genes.

Question 4

Modifications to Polypeptides

What are proteases?

- ase (enzyme)

Answer 4

• Any enzyme that breaks peptide bonds to digest/break down proteins
• Most are small and intentional for digestion.

Question 5

Modifications to Polypeptides

What is Ubiquitin?

Answer 5

• A small chain of proteins that help cells identiy which proteins need to be degraded (those that are damaged & not functional)
• Ubiquitin is recognised by the proteasome subunits that come together and digest the protien itno dipeptides

Question 6

Modifications to Polypeptides

What is Proteasome?

Answer 6

• A large cylinder shaped protein digesting complex
• Top and bottom of the cylinder recognize ubiquitin tags
• The core contains the cayalutic proteins that will break down the polypeptide using energy from ATP.

Question 7

Modifications to Polypeptides

What are the 5 steps involved in translation initiation?

Answer 7

• Amino-acyl tRNA synthetase attaches methionine to a tRNA with an UAC anticodon
• This initiater tRNA binds to the small ribosomal subunit to create the ternary complex
• Ternary complex binds to the 5’ end of the mRNA and moves along until the UAC anticodon recognises the first AUG start codon.
• The large subunits joins the small subunit with the AUG at the P site
• Then the next tRNA with the next amino acid arrives.

Question 8

Modifications to Polypeptides

What are 5 important modifications to polypeptides POST translation?

Answer 8

• Removal of methionine
• Chemical changes to R group side chains
• Folding to produce tertiary structure
• Removal of parts of the polypeptide in some cases
• Combining polypepties for quaternary structure

Question 9

Modifications to Polypeptides

What are modifications to preproinsulin?

Example

Answer 9

• Preproinsulin is translated as a 110 amino acid polypeptide, within the ER, a 24 amino acid is removed to make PROinsulin.
• Then two disfuldie bridges are broked by proteases and remove a 33 amino acid sequence.
• The remaining insulin protein is an alpha chain of 21 amino acids and a beta chain of 32 amino acids, held by disulfide bridges.

Question 10

Modifications to Polypeptides

Explain the possible reasons/necessity of proteases.

Remember, they degrade entire proteins and recycle amino acids

Answer 10

• Protein is no longer needed due to cell activity change
• Protein structure is changed by radicals/chemicals to be non-functional
• Protein became denatured/misfolded
• A mutation has generated a non-functional protein.

Question 11

Types of Mutations

What is a mutation?

Answer 11

• A random change in genetic material
• Can change a large section of DNA, like parts of the chromosome.
• More commonly, changes in specific base sequences of one single gene. (gene mutations)
• If a mutation occurs in a coding region - often changes the amino acid coded for & consequently structure of protein.

Question 12

Types of Mutations

Point mutation?

Often used when a base has been changed, synonomous with SUBSTITUTION.

Answer 12

• Only a single nucleotide is involed in a mutation.
• As one nucleotide has one single base, means that one single base is changed in the DNA sequence
• A single base could be changed, added or removed.

Question 13

Types of Mutations

What is a single nucelotide polymorphism?

SNP

Answer 13

• When a single base change creates a new alleles for that gene in the population
• Refer to mutations that result in genotypes found throughout the population (not just an individual)
• Can be the cause og genetic disorders/variations

Question 14

Types of Mutations

What is a frameshift?

Note: If three bases were added/deleted, no frameshift.

Answer 14

• When a base is added or removed from a gene can change the reading FRAME and shifts every base AFTER it into NEW codons, changing many amino acids.
• Important because DNA is a triplet code and mRNA is read in codons of three

Question 15

Types of Mutations

Describe Substitutions as a type of mutation

A type of POINT MUTATION

Answer 15

• One single base is replaced with another base.
• No. bases are unchanged and only one codon is impavted.
• Impac of change can vary from dramamtic to no impact depending on nature of new codon.

Question 16

Types of Mutations

Describe Insertions as a type of mutation

Answer 16

• One or MORE bases are added to the gene
• Often results in a frameshift changing every codon after the mutation and rendering the protein unable to function

Question 17

Types of Mutations

Describe Deletions as a type of mutation

Answer 17

• One or more bases are removed from the gene
• Usually causes a frameshift and leads to non-functional proteins.
• Cystic fibrosis is an exception - the result of a 3 base deletion which removes a single amino acid but doesn’t cause a frameshift.

Question 18

Types of Mutations

Describe sickle cell anaemia as a point mutation.

Answer 18

• A blood disorder where the red blood cell takes on a sickled shape
• The result of a single substitution of an Thymine base to an adenine base in a gene for haemoglobin B subnuit
• Changes a GAG codon which codes for glutamine to a GUG codon which codes for valine
• Alters the shape of the haemoglobin, causing a clustering of the protein.

Question 19

Types of Mutations

Describe Missense as an outcome of point mutations.

Answer 19

• When a single base is substituted to another base it always changes one codon, and when this leads to the change of a single amino acid = Missense.
• The degree of changes in the protein depends on the result of how similar the R-group were of the previous amino acid to the new one.

Question 20

Types of Mutations

Describe Nonsense as an outcome of point mutations.

Answer 20

• A coding amino acid gets changed by a substitution mutation to a STOP codon
• The change to the protein is much more dramatic - shorter proteins are often dysfunctional
• The clotting disorder Haemophilia is often the result of a nonesence mutation

Question 21

Types of Mutations

Describe Silent as an outcome of point mutations.

Third possible outcome of a single point substitution

Answer 21

• The change has no impact due to the degeneracy of the genetic code
• Can happen because multiple codons code the same amino acid
• When this occurs, there’s no change to the protein

Question 22

Types of Mutations

Describe how Huntington’s Disease as an Insertion Mutation.

Neurogenerative Disorder

Answer 22

• Caused by a specific type of insertion disorder called a trinucleotide expansion
• A healthy person has between 10-26 repeats of the CAG triplet within a gene
• A mutation causes this repeat to be repeated more - if exceeds 35040 repeats = Huntington’s disease

Question 23

Causes and Consequences of Mutations

What are mutagens?

And what are some examples?

Answer 23

• Any substance that causes mutations
• EG: UV radiation, radiactive substances and chemicals that can cause significant mutations.
• There’s also internal mutagens: enzymes that attack DNA, but most are external: radiation - can knock a base out of place altering the code.

Question 24

Causes and Consequences of Mutations

What is Satellite DNA?

Answer 24

• Non-coding DNA that plays a structural role in forming the centromere during cell division.
• Mutations occur more frequently in non-coding DNA

Question 25

# Causes and Consequences of Mutations Explain DNA replication and mutations

Answer 25

* Mutations can also occur due to **normal cellular activity** * During DNA replication, the **wrong base** can be added to growing strand * DNA polymerase should catch these, but they can go unnoticed * More likely the cuase of **point mutations** whuke mutagens are more significant **chromosomal mutations**

Question 26

# Causes and Consequences of Mutations What is the impact that mutations can have on Somatic Cells? ## Footnote Body Cells

Answer 26

* **Somatic cell are body cells** and these cells replicate by mitosis. * A mutation occuring in body cells can impac that person but **won't be passed onto offspring** * These mutations can lead to a no. faulty cells - can lead to **tumour formation** (cancer)

Question 27

# Causes and Consequences of Mutations What is the impact that mutations can have on germ cells? | Germ - SEX cells

Answer 27

* If a mutation occurs during **MEIOSIS** or in an existing sex cell - it will alter the **original DNA** that makes up the **zygote** * Responsible for **genetic diseases/disorder** these are **pased onto offspring** and create new alleles in the population.

Question 28

# Causes and Consequences of Mutations What is the role of mutations in natural selection?

Answer 28

* The starting point for natural selection is **genetic variation**, main contributor for this is mutations. * Mutations **creates new alleles of genes**, often mutations have no impact and is often deletirous and reduce reproductive success and disappears from the population.