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A-Level Biology > 4A DNA,RNA and Protein Synthesis > Flashcards

4A DNA,RNA and Protein Synthesis Flashcards

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1
Q

What is a genome?

A

A genome is the associated organisms complete set of genes.

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2
Q

What is a proteome?

A

A proteome is the associated organisms full range of proteins that they are able to produce.

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3
Q

What are chromosomes, and what are they made from?

A

Chromosomes are thread-like structures, each made up of one long molecule of DNA.

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4
Q

What cell contains chromosomes; eukaryotic, prokaryotic or both?

A

Both

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5
Q

In eukaryotes, what proteins are used to help DNA coil?

A

Histones

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6
Q

Describe how a DNA molecule coils to become a chromosome in an eukaryotic cell.

A

DNA will firstly wrap around multiple histone proteins.

DNA will then repeatedly keep wrapping and coiling around the histones, until it becomes a chromosome.

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7
Q

Give one feature of histone proteins that allow DNA to wrap around it.

A

Histone proteins give DNA support structurally.

Histone proteins also are used (in eukaryotic cells) for DNA to wrap around in order to become small enough to be stored in cells as chromosomes.

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8
Q

In an eukaryotic cell, list the organelles which have their own DNA.

A

Chloroplast

Mitochondria

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9
Q

Describe the structure of DNA in eukaryotic cells.

A

Firstly, DNA In eukaryotic cells are linear molecules that exist as chromosomes - thin-like structures each made up of one long molecule of DNA, supported and coiled to be compact by histone proteins.
They are found in the nucleus.

As well as this, eukaryotic cells have their own DNA in chloroplasts and mitochondria which are circular, as well as shorter than DNA molecules in the nucleus. They also do not have any histone proteins.

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10
Q

Use the correct word:

DNA in Chloroplasts and Mitochondria (Do/Don’t) have histone proteins.

A

The correct word is ‘Don’t’

DNA in Chloroplasts and Mitochondria don’t have histone proteins.

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11
Q

In Prokaryotic cells, where is the main DNA located?

A

The Cytoplasm

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12
Q

In Prokaryotic cells, are DNA wound to histones?

A

No

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13
Q

How does DNA condense to fit in a Prokaryotic cell?

A

DNA condenses to fit into the cell by a process called supercoiling.

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14
Q

What is a gene?

A

A gene is a sequence of DNA bases that code for either a polypeptide or functional RNA.

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15
Q

What forms the primary structure of a protein?

Following this, what determines the order of amino acids manufactured for a particular polypeptide?

A

The sequence of amino acids

The order of bases in a gene

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16
Q

What is a codon?

A

A codon is a sequence of three bases in a gene.

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17
Q

List the two things a gene can possibly code for.

A

A Polypeptide

Functional RNA

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18
Q

How are amino acids coded for in a gene?

A

Amino acids are coded for by a sequence of three bases in a gene, called a triplet.

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19
Q

What is functional RNA?

A

Functional RNA are RNA molecules other than mRNA which perform special tasks during protein synthesis.

For example, tRNA (transfer RNA) and rRNA (ribosomal RNA).

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20
Q

In genes that code for polypeptides, a gene in a certain type of cell can contain sections that don’t code for polypeptides at all.

Which type of cell has this?

A

Eukaryotic

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21
Q

What is an intron?

A

a segment of a DNA or RNA molecule which does not code for proteins.

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22
Q

What is an exon?

A

A segment of DNA or RNA molecule which codes for proteins.

23
Q

Genes that code for polypeptides contain sections which do not code for polypeptides; these are known as Introns.

Which process removes introns from genes?

A

Splicing

24
Q

In eukaryotic DNA, there may be a section outside of a gene that repeat over and over, for example:

CCTTCCTTCCTT

What is this called?

A

Multiple repeats

25
Q

What is an allele?

A

An allele is a different version of the same gene.

In other words, alleles are basically slightly different versions of the same polypeptide, having the order of bases they are made in slightly different.

26
Q

What is a homologous pair of chromosomes?

A

Homologous pairs of chromosomes are pairs of matching chromosomes, for example:

Humans have 23 pairs of chromosomes, meaning 46 in total. Two number 1’s, two number 2’s, etc.

A homologous pair would, for example, be the two number 1’s, a pair of matching chromosomes.

27
Q

In a homologous pair of chromosomes, can the alleles expressed between them vary?

A

Yes. For example, if you have a chromosome pair which determines eye color, each chromosome in the pair can code for different alleles.

28
Q

Describe two similarities between chromosomes in a homologous pair.

Describe one difference between chromosomes in a homologous pair.

A

Similarities:

They are the same size
They contain the same genes, so code for the same characteristic

Differences:

They may contain different alleles

29
Q

In a homologous pair of chromosomes, what is a locus?

A

A locus is the specific physical location of a gene or other DNA sequence on a chromosome coding for a specific characteristic.

On a homologous pair of chromosomes, which have the same genes, the gene coding for a specific characteristic on one chromosome will have the same location as another. regardless if the alleles are different.

30
Q

List the two types of RNA (excluding rRNA).

A

tRNA

mRNA

31
Q

In what stage of protein synthesis is mRNA made?

A

Transcription

32
Q

Describe one function of mRNA.

A

mRNA carries the genetic code from the DNA to the ribosomes, where it’s used to make a protein during translation.

33
Q

What is mRNA made of?

A

mRNA is made of a single polynucleotide strand.

34
Q

Label A and B:

https://media.discordapp.net/attachments/352951793187029005/812419555548594216/unknown.png?width=396&height=562

A 
A = Anticodon
B = Amino acid binding site
35
Q

Outline the structure of tRNA.

A

tRNA is a single polynucleotide strand that’s folded into a clover shape.

Hydrogen bonds between specific base pairs hold the molecule in this shape.

Each tRNA molecule has a specific sequence of three bases at one end called an anticodon, as well as an amino acid binding site at the other end.

36
Q

What is tRNA involved in?

A

Translation

It carries the amino acids that are used to make proteins to the ribosomes.

37
Q

Describe the process of Transcription.

A

During transcription, an mRNA copy of a gene is made from DNA.

Transcription starts when RNA polymerase (an enzyme) attaches to the DNA double helix at the beginning of a gene.

In eukaryotes, the hydrogen bonds between the two DNA strands in the gene are broken by a DNA helicase attached to the RNA polymerase.

This separates the strands and the DNA molecule uncoils at that point, exposing some of the bases.

One of the strands are then used as a template to make an mRNA copy.

The free floating RNA nucleotides are then attracted to the exposed base complementary to them, lining up alongside it.
Specific, complementary base pairing means that the mRNA strand ends up being a complementary copy of the DNA template, with Uracil replacing Thymine.

Once the RNA nucleotides have paired up with their specific bases on the DNA strand, they’re joined together by RNA polymerase by condensation reactions, forming an mRNA molecule.

The RNA polymerase moves along the DNA, separating the strands and assembling the mRNA strand.

The hydrogen bonds between the uncoiled strands of DNA re-form once the RNA polymerase has passed by and the strands coil back into a double-helix.

When RNA polymerase reaches a particular sequence of DNA called a stop signal, it stops making mRNA and detaches from the DNA.

In eukaryotes, mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm, where the next stage of protein synthesis takes place.

38
Q

In Eukaryotes, where does transcription take place?

A

Nucleus

39
Q

In Prokaryotes, where does transcription take place?

A

Cytoplasm

40
Q

Describe why prokaryotic mRNA does not need to be spliced.

A

Prokaryotic mRNA does not have introns, and therefore does not need to be spliced.

41
Q

In Eukaryotes, where does splicing occur?

A

Nucleus

42
Q

In Eukaryotes, what happens to pre-mRNA as a result of splicing?

A

the pre-mRNA will lose all it’s introns and the exons are joined together, forming mRNA strands.

43
Q

What is pre-mRNA?

A

mRNA that has not been spliced yet (still contains introns).

44
Q

Explain why it is important for a pre-mRNA coding for a polypeptide to be spliced before it is sent for translation.

A

It is important for pre-mRNA coding for a polypeptide to be spliced due to the fact that introns, which are parts of the gene that do not express the instructions needed to create a polypeptide, must be removed in order for the polypeptide to be properly assembled during translation.

If they are not removed, the polypeptide won’t be made properly in translation.

45
Q

Describe the process of Translation.

A

In both eukaryotes and prokaryotes, translation occurs at the ribosomes in the cytoplasm.

During translation, amino acids are joined together to make a polypeptide chain (protein), following the sequence of codons carried by the mRNA.

The mRNA attaches itself to a ribosome, and transfer RNA molecules carry amino acids to it.

ATP provides the energy needed for the bond between the amino acid and the tRNA molecule to form.

A tRNA molecule, carrying an amino acid by it’s amino acid binding site, with an anticodon that’s complementary to the first codon on the mRNA, attaches itself to the mRNA by complementary base pairing.

A second tRNA molecule attaches itself to the next codon on the mRNA in the same way.

The amino acids attached to the tRNA molecules are joined by a peptide bond. The first tRNA molecule moves away, leaving its amino acid behind.

A third tRNA molecule binds to the next codon on the mRNA. It’s amino acid binds to the first two and the second tRNA molecule moves away.

This process continues, producing a chain of linked amino acids (a polypeptide chain), until there’s a stop signal on the mRNA molecule.

The polypeptide chain moves away from the ribosome and translation is complete.

46
Q

What is the genetic code?

A

The sequence of codons in mRNA which code for specific amino acids.

47
Q

The genetic code is described as non-overlapping. What does this mean?

A

No single base take part in the formation of more than one codon.

For example, in a genetic code of UCA GAU:

The genetic code is seen as non-overlapping as the three bases for one codon, UCA, does not contribute for the formation of any other codon, therefore each base on a nucleotide is unique to one codon.

48
Q

The genetic code is described as degenerate. What does this mean?

A

There are more possible combinations of triplets than there are amino acids (20 amino acids but 64 possible triplets).

This means that some amino acids are coded for by more than one codon, therefore:

Although each codon is specific for only one amino acid (or one stop signal), the genetic code is described as degenerate, because a single amino acid may be coded for by more than one codon.

49
Q

The genetic code is described as universal. What does this mean?

A

The same codons code for the same amino acids in all living things.

For example, UAU codes for tyrosine in all livings things.

50
Q

A mRNA gene expresses the following codons:

UCU CUA UAU GUG

List, in order, the sequence of amino acids that will be manufactured from this sequence in translation:

CGC = Arginine
UCU = Serine
CUA = Leucine
GCA = Alanine
GUG = Valine
UAU = Tyrosine
A

Serine, Leucine, Tyrosine and Valine

51
Q

A mRNA gene expresses the following codons:

CGG UAU GCU AUC

List, in order, the sequence of anticodons complementary to the sequence.

A

GCC AUA CGA UAG

52
Q

A DNA gene expresses the following codons:

TCG ATG CTA GCT TAC TCC

List, in order, the sequence of mRNA complementary to the sequence.

A

AGC UAC GAU CGA AUG UGG

53
Q

To investigate how two new drugs affect nucleic acids and their role in protein synthesis, bacteria were
grown in normal conditions for a few generations, then moved to media containing the drugs.

After a short period of time, the concentration of protein and complete strands of mRNA in the bacteria were analyzed.
The results are shown in the bar graph:

https://media.discordapp.net/attachments/352951793187029005/812767297608744990/unknown.png

Outline and explain the results shown on the graph.

A

Firstly, both mRNA and protein concentration were lower in the presence of drug 1 compared to the no-drug control group.

This suggests that drug 1 affects the production of full length mRNA, as mRNA concentration was lower, so there’s not as much mRNA for protein synthesis during translation, causing a lower concentration of protein.

mRNA production in the presence of drug 2 was unaffected, but less protein was produced - 3mgcm^-3 compared to 8mgcm^-3.
This suggests that drug 2 interferes with translation, as mRNA was produced, but less protein was translated from it.

A-Level Biology (20 decks)

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