3.1.8 Protein Synthesis Flashcards

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1
Q

When is mRNA made?

A

During transcription

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2
Q

Describe the structure of mRNA

A

It’s a single polynucleotide strand (& has groups of 3 adjacent bases)

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3
Q

What are 3 adjacent bases called?

A

Codons (or sometimes called triplets or base triplets)

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4
Q

What does mRNA do?

A

Carries genetic code from DNA to ribosomes & is then used to make a protein during translation

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5
Q

What does tRNA do?

A

Carries amino acids that are used to make proteins to ribosomes

(involved in translation)

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6
Q

Describe the structure of tRNA

A

It’s a single polynucleotide strand that’s folded into clover shape

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7
Q

How does tRNA stay in a clover shape?

A

H-bonds between specific base pairs hold it in shape

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8
Q

What does every tRNA molecule have? (2x)

A
  • Anticodon at one end - specific sequence of 3 bases
  • An amino acid binding site at other end
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9
Q

What is the main thing that happens in transcription?

A

mRNA copy of gene is made from DNA

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10
Q

In eukaryotic cells, where does transcription takes place?

A

Nucleus

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11
Q

Describe the stages in transcription

A
  1. DNA helicase (in eukaryotes) breaks H-bonds between 2 DNA strands (in beginning of a gene)
  2. Only one DNA strand acts as a template (to make mRNA copy)
  3. Free bases in RNA nucleotides are attracted to exposed bases
  4. Attraction occurs according to complementary base pairing (∴ mRNA strand becomes a complementary copy of DNA template strand)
  5. RNA nucleotides are joined together by RNA polymerase
  6. (In eukaryotes) mRNA moves out through nuclear pore
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12
Q

Where does transcription take place in prokaryotes?

A

Cytoplasm

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13
Q

When does the RNA polymerase stop making mRNA and detachs from DNA in transcription?

A

When RNA polymerase reaches a particular sequence of DNA called stop signal

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14
Q

Where does translation occur in both eukaryotes and prokaryotes?

A

At ribosomes in cytoplasm

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15
Q

What is the main thing occuring during translation?

A

Amino acids are joined together to make polypeptide chain, following the sequence of codons (triplets) carried by mRNA

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16
Q

Describe the stages in translation

A
  1. mRNA moves into cytoplasm & attaches to ribosome
  2. tRNA carry amino acids to it
  3. Specific tRNA molecule for specific amino acid
  4. Anitcodon of tRNA binds to complementary codon on mRNA (attaches by specific base pairing)
  5. Peptide bond forms between amino acids
  6. tRNA detaches and collects another amino acid
  7. Ribosome moves along mRNA = forming a long polypeptide chain
17
Q

What determines how the folded protein structure of protein will be?

A

Position of R groups in polypeptide chain

18
Q

What issue can happen as polypeptide chains are formed on a ribosome?

A
  • Regions where amino acids have hydrophobic R groups can to clump together or join with other hydrophobic molecules spontaneously
  • Leads to forming a non-functional, ‘mis-folded’ protein & many of them = disease
19
Q

What do cells produce to ensure the polypeptide chains made on ribosomes are folded correctly?

A

Chaperone proteins

20
Q

Describe the role of chaperone proteins (3)

A
  • Chaperone proteins bind to hydrophobic groups (on the secretory proteins)
  • Prevent incorrect hydrophobic interactions
  • Allows protein to be correctly folded
21
Q

Where are chaperone proteins are found?

A

In endoplasmic reticulum

22
Q

What is the genetic code?

A

Sequence of base triplets (codons) in mRNA which code for specific amino acids

23
Q

Name 3 qualities of the genetic code

A
  1. Non-overlapping
  2. Degenerate
  3. Universal
24
Q

Describe how genetic code is non-overlapping

A

Each base triplet is read in sequence only once

25
Q

Describe how genetic code is degenerate

A

Some amino acids are coded by more than one base triplet

e.g. tyrosine can be coded for by UAU or UAC

26
Q

Describe how genetic code is universal

A

Same specific base triplets code for same amino acids in all living things

e.g. UAU codes for tyrosine in all organisms

27
Q

What are start/stop signals (or codons)?

A

Triplets that tell the cell when to start/stop production of a protein

28
Q

Transcription Makes _______ Products in Eukaryotes and Prokaryotes

A

Different

29
Q

What does transcription make in eukaryotes?

A

pre-mRNA

30
Q

What is pre-mRNA?

A

mRNA strands containing introns and exons

31
Q

Why does pre-mRNA contain introns and exons?

A

Introns and exons are both copied into mRNA during transcription

32
Q

Name and describe the process how pre-mRNA is made into mRNA

A

Process called splicing occurs: introns are removed and exons join together = forming mRNA strands

33
Q

Where does splicing occur?

A

In nucleus

34
Q

What does transcription make in prokaryotes?

A

mRNA - it’s produced directly from DNA without splicing

35
Q

Transcription

What enzyme separates the strands of DNA in prokaryotes?

A

RNA polymerase

36
Q

Explain why the percentage of bases from the middle part of the chromosome and end part are different (2)

A
  • Different genes
  • Have different base sequences
  • Codes for different proteins
37
Q

Different sequences of bases code for different proteins. Explain how. (2)

A
  • Protein made up of (chain of) amino acids
  • Each amino acid has its own base code
38
Q

Explain how copying bases more than once may give rise to differences in the protein (2)

A

Changes base sequence of later triplets/amino acid codes