Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Medical Cell Biology 🌟 > SESSION 8 > Flashcards

SESSION 8 Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Define codon

A

Triplet of nucleotides in mRNA that encode the information for a specific amino acid in a protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Define stop codon

A

A codon in mRNA that signals the end of translation

UAA, UAG, and UGA are stop codons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Define start codon

A

A codon present in mRNA that signals the location for translocation to begin
The codon AUG functions as a start codon and codes for the amino acid methionine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Define structural genes

A

Genes that code for amino acid sequence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe making a polynucleotide

A
  • needs an enzyme
  • needs activated substrates
  • needs a template
  • 3 stage process: initiation, elongation and termination
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Describe making DNA

A
  • enzyme, DNA polymerase
  • activated substrates, dNTPs
  • template, DNA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe making RNA

A
  • enzyme- RNA polymerase
  • activated substrate, NTPs
  • template DNA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Describe making a polypeptide

A
  • enzyme, ribosome
  • activated substrate, amino acids
  • template, mRNA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Explain that the process of gene expression involves two main stages

A

Transcription: the production of messenger RNA (mRNA) by the enzyme RNA polymerase, and the processing of the resulting mRNA molecule

Translation: the use of mRNA to direct protein synthesis, and the subsequent post- translational processing of the protein Molecule

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Define introns

A

DNA sequences present in some genes that are transcribed but are removed during processing and therefore are not present in mature mRNA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Define exons

A

DNA sequences that are transcribed, joined t other exon during mRNA processing, and translated into amino acid sequence f a protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Define cap

A

A modified base (G) attached to the 5’ end of eukaryotic mRNA molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Define poly- a- tail

A

A series of nucleotides added to the 3’ end of mRNA molecules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe the process and role of transcription

A

Initiation:
Initiation code is recognised- 5’ TATA 3’
Transcription factors (regulating genes that are expressed) binds at this code, upstream of the gene, and attract RNA polymerase too start mRNA production
RNA polymerase separated the DNA strands for the RNA nucleotides to bind along the template strand

Elongation:
RNA polymerase travels along the template strand, picking up base pairs and copying them onto a complementary RNA strand
This process continues until the genetic sequence is ‘transcribed’ onto the new RNA molecule - mRNA

Termination:
When the gene has been transcribed the mRNA adds a methyl- guanine ‘cap’ to the 5’ end
This methyl guanine is bonded with 5’ - 5’ triphosphate linkage to stabilised the mRNA
At the 3’ there is a stop codon that activates cleavage of the mRNA (AAUAA) then the 3’ end is polyadenylated - lots of adenine nucleotides are added- this is known as tailing
Pre- mRNA molecule is released and the DNA strands re- form a double helix

Processing:
After transcription the RNA molecule is processed:
Introns are removed and the exons are spliced together to form a. Mature mRNA molecule consisting of a single protein- coding sequence
Endonuclease- breaks within the polynucleotide
Exonuclease- degrades polynucleotide from 5’ or 3’ end

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Contrast the different type of RNA molecules, i.e. MRNA, rRNA and tRNA

A

MRNA

  • messenger RNA
  • 2% of RNA
  • 100, 000s kinds / few copies

RRNA:
- ribosomal RNA
- >80% of RNA
- few kinds but with many copied of each
RRNA is used to bind to the mRNA and provides the location for tRNA
- in eukaryotes the rRNA is 80s- 60s and 40s subunits
- prokaryotes, e.g. E Coli the rRNA is 70s- 50s and 30s subunits

TRNA:
- transfer RNA
- 15% of RNA
- 100 kinds with very many copies of each
TRNA is uncharged without a bound amino acid, and once it is charged it is referred to as an aminoacyl- tRNA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe the process and role of translation

A

Initiation:
At the 5’ cap the mRNAs the 40s subunit with Met- tRNA binds
For translation to start, a starting codon must be recognised
This is 5’ AUG which is a specific codon only to one amino acid- methionine
The anticodon for this (found on the tRNA) is 5’ CAU
The 60S subunit then binds for elongation to occur

Elongation:
The rRNA has two sites for tRNA to bind:
- the P site is for the site holding the peptide chain
- the A site is for the site accepting the tRNA

Met tRNA occupies the P site and then another aminoacyl tRNA enters the ribosome to occupy the A site (requires GTP)

The methionine forms a peptide bond with the next aminoacyl tRNA making the tRNA the P site now uncharged
This now leaves the ribosome moves along
The binding of the two amino acids requires peptidyl transferase

Termination:
The termination of a polypeptide chain forming requires a stop codon to be read on the mRNA
Stop codons can be 5’UAA, 5’UAG, 5’UGA
There aren’t any tRNAs that can bind to these codons and so the peptide and tRNA are hydrolysed to release the protein into the cytoplasm

17
Q

Comparisons of ribosomes in eukaryotes and prokaryotes

A

Ribosomes are a mixture of ribosomal proteins and ribosomal RNA (rRNA), and consist of a large subunit and a small subunit

Prokaryotes:

  • 3 rRNAs + 56 proteins
  • 30S + 50S subunits
  • 70S subunit

Eukaryotes

  • 4 rRNAs + 82 proteins
  • 40S + 60S subunits
  • 80S subunits
18
Q

Define the term gene

A

A unit of heredity
A transcription unit, i.e. A length of DNA on a chromosome that contains the code for a protein (or RNA) as well as sequences necessary for its expression, such as promoter and terminator sequences and introns

19
Q

Define a wobble base

A

A single tRNA species to recognise more than one codon

E.g. G can sometimes recognise not just a C but a U and can form 2 hydrogen bonds

20
Q

Define both the N- terminus and the C- terminus

A

N- terminus: the end of a polynucleotide or protein that has a free amino acid group

C- terminus: the end of a polypeptide o protein that has a free carboxyl group

21
Q

List and summarise the major reactions involved in the process of RNA maturation in eukaryotes and explain their importance in gene expression

A

Capping: adds a methyl- guanine with a 5’- 5’ triphophate linkage

Polyadenyltion (tailing): adds a series of Aden Ines to the end of the mRNA

Splicing: removes introns using endonuclease and exonuclease

  • endonuclease break within the polynucleotide. They can be non- specific or specific
  • exonuclease degrade the polynucleotides from the ends. Can be 5’ or 3’ specific
22
Q

Explain the nature of the triplet code and be able to apply the genetic code

A

The triplet code is degenerative- there is more than one code per amino acid

23
Q

Comprehend the implications of the degeneracy of the genetic code

A

Substitutions in the genetic code can lead to a different primary sequence. This can affect the tertiary structure of a protein
A mutation that affects the stop codon ca lead to longer polypeptide chains that will be malfunctional
E.g. Haemoglobin normally 141 amino acids long. A mutation in the sop codon can lead it to be longer

24
Q

Compare and contrast gene expression in mammalian and bacterial cels and explain how the difference can be exploited clinically

A

Bacteria have:

  • simple promotors
  • different transcription factors
  • single RNA poplymerase
  • coupled transcription- translation
  • no- post transcriptional processing
  • short lived mRNAs
  • simpler ribosomes
  • distinctive translation initials mechanism
  • different translation factors
25
Q

Predict the effects of various mutations in a gene

A

The severity of the effect caused by a mutation depends on the amount of difference in the protein is caused
For example if an amino acid is switched for one with simple properties there is unlikely to be a large effect. However if it is swapped with different properties the effects may be profound (e.g. Sickle cell anaemia)
Premature or delayed stop codon will cause truncated/ elongated proteins that may not function correctly if at all

26
Q

Explain how mutations outside the coding region can affect gene expression

A

Mutations to promotor regions where transcription bind affect gene expression, to other constitutively active or deactivate it

27
Q

Describe the mechanisms of gene regulation

A
  • regulating the rate of transcription
  • regulating the processing of RNA molecules
  • regulating the stability of mRNA molecules
  • regulating the rate of translation
28
Q

Explain why there are only few kinds of rRNA and 100, 000s kinds of mRNA

A

You only need 4 different types of rRNA, the number to make up a ribosome
Whereas you need many mRNAs as you have many proteins

There are however many copies of rRNA as you need many to make many ribosomes

29
Q

Explain why DNA polymerase are capable of editing and error correction, whereas the capacity for error correlation in RNA polymerase appears quite limited

A

RNA compared to DNA is expendable and preservation is not as vital
RNA is unstable by design so it can degrade readily when required

DNA however is very stable to ensure errors are not incorporated

Medical Cell Biology 🌟 (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions