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IB BIOLOGY > D1.2 Protein Synthesis > Flashcards

D1.2 Protein Synthesis Flashcards

1
Q

Define transcription

A

Transcription = is the process of synthesizing RNA using DNA as a template

  • RNA is single-stranded, so transcription occurs along only one of the two DNA strands
  • Genes can be transcribed multiple times to produce as many RNA copies as needed
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2
Q

List the roles of RNA polymerases in the process of transcription (7 actions it carries out)

A

RNA:

  • Binds to the DNA at the gene’s start site
  • Unwinds the DNA double helix, separating it into two strands (template and coding)
  • Moves along the template strand
  • Positions RNA nucleotides to match bases on the template strand
  • Links RNA nucleotides with covalent bonds to form a continuous RNA strand
  • Detaches the RNA from the template strand once transcription is complete
  • Reforms the DNA double helix
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3
Q

State the complementary base pairing utilized in transcription

A

in DNA: ATGC

  • Cytosine (C) & Guanine (G)
  • Thymine (T) & Adenine (A)

in RNA: AUGC

  • Guanine (G) & Cytosine (C).
  • Adenine (A) & Uracil (U)
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4
Q

Distinguish between the sense and antisense strands of DNA

A
  • Sense strand (coding strand): Has the base sequence that is copied into RNA + is identical to the RNA sequence, except with thymine instead of uracil
  • Antisense strand (template strand): used as a template for RNA synthesis + is complementary to the sense strand
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5
Q

How is the stability of information stored in DNA maintained during (+ after) transcription?

A

DURING TRANSCRIPTION:

  • RNA temporarily splits DNA into single strands, using the template strand for transcription.
  • The DNA base sequence remains unchanged during transcription.

AFTER TRANSCRIPTION:

  • the two DNA strands quickly re-pair with complementary bases linked by hydrogen bonds
  • DNA strands are exposed briefly, minimizing the risk of chemical changes that could lead to mutations
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6
Q

Why is the stability of DNA templates important for cellular function?

A
  • DNA templates must remain stable since they may be transcribed many times during a cell’s life.
  • Frequent mutations could lead to RNA errors, causing proteins with incorrect amino acid sequences.
  • Mutated proteins may function less effectively, which could negatively affect cellular processes.
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7
Q

What is gene expression?

A

Gene expression = the process by which information carried by a gene has observable effects on an organism

  • It involves the production of proteins that determine observable characteristics
  • The sequence of bases in genes specifies the amino acid sequence in a polypeptide, which forms a protein
  • Proteins, not genes themselves, directly or indirectly affect an organism’s traits
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8
Q

What are the major steps of gene expression?

A
  • Transcription: The DNA sequence of a gene is copied into RNA.
  • Translation: The RNA is used to build a specific polypeptide (protein) by linking amino acids in a sequence.
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9
Q

How does the pattern of gene expression relate to cell differentiation?

A

the pattern of gene expression is how cells differentiate for specific functions

  • Different genes are switched on or off in different cells at different times
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10
Q

What is the role of transcription in regulating gene expression?

A

Transcription = the first stage of gene expression + the key point where gene expression can be switched on or off

  • Not all genes are transcribed at the same time (only some genes are active in a cell at any given moment)
  • Some genes may never be transcribed during the life of a cell (ex. insulin gene in non-pancreatic cells)

Transcription regulates which proteins are produced, thus controlling cell function and identity

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11
Q

Define translation

A

translation = the process of polypeptide (protein) synthesis from an mRNA (messenger RNA) sequence

  • The sequence of bases in the mRNA is used to determine the correct sequence of amino acids in a polypeptide
  • Amino acids are linked together in the correct order based on the genetic code carried by mRNA
  • Translation = essential for turning genetic information into functional proteins
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12
Q

State the location of translation in cells

A

Translation occurs in the cytoplasm (on ribosomes)

In eukaryotic cells (has nucleus):

  • RNA is transcribed in the nucleus and then transported out to the cytoplasm to be translated

In prokaryotic cells (no nucleus):

  • Translation and transcription occur in the same part (cytoplasm) of the cell, since there is no nucleus
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13
Q

Outline the roles of mRNA, ribosomes, and tRNA in translation

A

mRNA: (messenger RNA)

  • Carries the genetic code from DNA to the ribosome, specifying the amino acid sequence of the polypeptide
  • It has a binding site for the ribosome and contains codons, including a start and stop codon to indicate where translation begins and ends

tRNA: (transfer RNA)

  • Translates the mRNA codons into the amino acid sequence.
  • Each tRNA has an anticodon that pairs with mRNA codons and an attachment site for the corresponding amino acid.

Ribosomes:

  • Provide the site for translation.
  • They consist of two subunits and facilitate the linking of amino acids by forming peptide bonds.
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14
Q

What are the structures of mRNA and tRNA?

A

mRNA:

  • A long, single-stranded molecule that carries genetic information from DNA.
  • It has a 5’ cap, a coding region with codons, and a 3’ poly-A tail.

tRNA:

  • A cloverleaf-shaped molecule with an anticodon at one end that binds to the mRNA codon and an amino acid attachment site at the other end.
  • Each tRNA has a unique shape for its specific amino acid.
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15
Q

What is the structure of ribosomes, including the small and large subunits and the tRNA binding sites?

A

Ribosome structure:

Small subunit:

  • Contains a binding site for mRNA

Large subunit:

  • Contains three binding sites for tRNA and a catalytic site to form peptide bonds between amino acids

tRNA binding sites:

  • A site (Aminoacyl site): Binds to the tRNA carrying the next amino acid.
  • P site (Peptidyl site): Holds the tRNA with the growing polypeptide chain.
  • E site (Exit site): Where tRNA exits the ribosome after its amino acid is added to the chain.
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16
Q

What complementary base pairing is utilized in translation?

A

In translation, the complementary base pairing between mRNA and tRNA ensures accurate protein synthesis

in RNA:

  • Adenine (A) pairs with Uracil (U)
  • Cytosine (C) pairs with Guanine (G)

This base pairing ensures that tRNA can correctly bind to mRNA and deliver the appropriate amino acid

17
Q

What are codons and anticodons?

A

Codon:

  • A sequence of three bases in mRNA that codes for a specific amino acid.

Anticodon:

  • A sequence of three bases in tRNA that is complementary to a codon in mRNA.

The anticodon of tRNA pairs with the codon in mRNA during translation to ensure the correct amino acid is added to the growing polypeptide chain.

18
Q

How are hydrogen bonds formed between codons and anticodons?

A

Hydrogen bonds form between the complementary bases of the codon (on mRNA) and the anticodon (on tRNA)

  • The three bases of the tRNA anticodon pair with the three complementary bases of the mRNA codon
  • These hydrogen bonds help stabilize the binding of the tRNA to the mRNA, ensuring accurate translation and the correct amino acid is added
19
Q

Why is a sequence of three nucleotides required to code for the 20 amino acids?

A
  • There are four bases (A, T, G, C) and 20 amino acids, so a single base cannot code for one amino acid
  • A two-base combination provides only 16 possible combinations, which is too few to code for all 20 amino acids
  • SO, a triplet code is used, with three bases per codon, resulting in 64 possible combinations, which is more than enough to code for all 20 amino acids

–> This allows for accurate encoding of the amino acid sequences needed for polypeptide formation

20
Q

What do the terms codon, degenerate, and universal mean in relation to the genetic code?

A
  • Codon: A sequence of three bases on mRNA that codes for a specific amino acid
  • Degenerate: means that multiple codons can code for the same amino acid (the genetic code is degenerate because it can do this)
  • Universal: means that the genetic code is used by all living organisms and viruses (with only minor variations in some cases)
21
Q

How do you use the genetic code table to determine the amino acid sequence coded for by a given DNA or RNA sequence?

A

know how to do this!

STEP 1:

  • Identify codons for amino acids

STEP 2:

  • Translate a sequence of mRNA codons into an amino acid sequence
    –> (ex. if the mRNA sequence is GCA, it codes for alanine)

for a DNA sequence:

  • Find the DNA sequence transcribed into mRNA

–> identify the complementary base pairs (ex. for DNA codon = CGT, the complementary mRNA codon = GCA)
–> So, the DNA codon CGT would transcribe into the mRNA codon GCA, which codes for the amino acid alanine

22
Q

Outline the process of translation elongation, including codon recognition, bond formation and translocation ( 7 steps)

A

1. tRNA Activation:

  • An activating enzyme binds to a tRNA molecule and attaches the specific amino acid that matches the tRNA’s anticodon

2. Codon Recognition:

  • The tRNA carrying the amino acid binds to the A (aminoacyl) site on the ribosome.
  • The anticodon of the tRNA pairs with the next codon on the mRNA through complementary base pairing.

3. Bond Formation:

  • The amino acid on the tRNA is linked to the growing polypeptide chain by the formation of a peptide bond.
  • The tRNA now holds the entire polypeptide.

4. Translocation 1:

  • The ribosome moves along the mRNA by one codon, causing the tRNA to shift from the A site to the P (peptidyl) site.
  • The anticodon of the tRNA remains paired with the codon on the mRNA.

5. Polypeptide Transfer:

  • The polypeptide is transferred from the tRNA in the P site to the tRNA in the A site, which is carrying the next amino acid.

6. Translocation 2:

  • The tRNA moves from the P site to the E (exit) site.
  • The ribosome moves along the mRNA by one more codon, causing the tRNA’s anticodon to separate from the mRNA codon and the tRNA to exit the ribosome.

7. Cycle Repeats:

  • The process restarts with a new tRNA arriving at the A site and linking a new amino acid to the growing polypeptide chain.
23
Q

Define gene mutation

A

A gene mutation = a change in the base sequence of a gene

  • Even a small mutation can change a codon to a different one
  • This can result in a different amino acid being coded!
24
Q

what is a base substitution?

A

A base substitution usually changes one amino acid in the resulting polypeptide, which may or may not affect the protein’s structure or function

25
Q

What is the cause of sickle cell anemia?
(including the differences in the HbA and HbS alleles)

A

Sickle cell anemia is caused by a single base substitution in the gene for beta-globin (part of hemoglobin)

  • The normal allele = HbA, while the mutated allele = HbS
  • The mutation (from HbA to HbS) changes the sixth codon of the beta-globin gene from GAG (glutamic acid) to GUG (valine)

–> This causes the HbS allele to code for valine (GUG) instead of glutamic acid (GAG) at position 6 of the hemoglobin protein

26
Q

What is the difference in RNA sequences in the transcription of the HbA and HbS alleles?

A
  • In HbA, the sixth codon of the mRNA is GAG (which codes for glutamic acid).
  • In HbS, the sixth codon of the mRNA is GUG (which codes for valine).

–> This single base substitution in the DNA (GAG → GUG) is reflected in the mRNA during transcription.

27
Q

What is the difference in amino acid sequences in the translation of the HbA and HbS alleles?

A
  • In HbA, the sixth amino acid in the polypeptide is glutamic acid (from the codon GAG)
  • In HbS, the sixth amino acid is valine (from the codon GUG).

–> This small change in the amino acid sequence significantly alters the structure and behavior of the hemoglobin protein.

28
Q

What are the consequences of the HbS mutation on the structure and function of the hemoglobin protein?

A

The substitution of valine for glutamic acid causes hemoglobin molecules to link together in low oxygen conditions

–> This results in the formation of rigid chains that distort red blood cells into a sickle shape

–> The sickled cells are less flexible and can become trapped in capillaries, blocking blood flow and causing tissue damage

–> The red blood cells are damaged and have a shorter lifespan, typically only about 4 days, compared to the usual 120 days

29
Q

What are the symptoms of sickle cell disease?

A
  • Reduced blood flow (due to sickled cells blocking capillaries)
  • Anaemia (because sickle cells have a much shorter lifespan, and the body cannot replace them quickly enough)
  • Fatigue and weakness
30
Q

POSSIBLE TEST Q: Describe transcription

A

Transcription is the process by which RNA is synthesized from a DNA template. RNA polymerase, an essential enzyme in transcription, binds to the promoter region of the gene, marking the start of the process. The DNA unwinds, and the antisense strand is used as a template to produce a complementary RNA strand. This strand is synthesized in the 5’ to 3’ direction by RNA polymerase.

During elongation, RNA polymerase adds complementary RNA nucleotides to the growing RNA strand. In transcription, adenine (A) in the DNA pairs with uracil (U) in RNA, and cytosine (C) pairs with guanine (G). The resulting RNA is complementary to the antisense strand and identical to the sense strand (with uracil replacing thymine).

The process concludes when RNA polymerase reaches a terminator sequence, signaling the end of transcription. The mRNA is then released and will undergo translation to form a protein. Transcription is crucial in gene expression, as it is the first step in synthesizing proteins that determine cellular function.

IB BIOLOGY (11 decks)

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