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A Level - Biology > 8: DNA, genes and protein synthesis > Flashcards

8: DNA, genes and protein synthesis Flashcards

1
Q

What is a gene?

A

A sequence of DNA bases that codes for the amino acid sequence of a polypeptide OR a functional RNA

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2
Q

What are the different RNA forms?

A

rRNA - Ribosomal
tRNA - Transfer
mRNA - Messenger

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3
Q

How does DNA exist in eukaryotic cells?

A

Linear DNA molecules that exists as chromosomes
One long molecule of DNA
Found in the nucleus coiled very tightly

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4
Q

How is a DNA wound in eukaryotic cells?

A

Really long so wound up around histone proteins to fit in nucleus

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5
Q

What is a histone?

A

A protein that DNA is wound around in eukaryotic cells

Supports the DNA

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6
Q

Other than the nucleus, where is DNA found in a eukaryotic cell?

A

Mitochondria and chloroplasts

Circular and shorter - no histones

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7
Q

How does DNA exist in prokaryotic cells?

A

Shorter than chromosomes and circular
No histones
Super-coiling so it fits in the cell

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8
Q

What is a cell’s genome?

A

Complete set of genes in the cell

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9
Q

What is a cells’ proteome?

A

Full range of proteins that a cell is able to produce

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10
Q

What does the order of bases determine?

A

The order of amino acids to form a particular polypeptide

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11
Q

What is an amino acid coded by ?

A

DNA Triplet

Three bases from a gene

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12
Q

What is the use of genes that don’t code for polypeptides?

A

Codes for functional RNA

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13
Q

What is functional RNA?

A

RNA other than mRNA

Performs special tasks (tRNA & rRNA)

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14
Q

What is a chromosome?

A

A thread-like structure made of protein and DNA

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15
Q

What is an allele?

A

One of a number of alternative forms of a gene

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16
Q

What is the locus?

A

Position of a gene on a chromosome/DNA molecule

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17
Q

What is a gene?

A

A section of DNA on a chromosome coding for the amino acid sequence for one or many polypeptides

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18
Q

What does homologous mean?

A

A pair of chromosomes, one maternal and one paternal

Same gene loci therefore determines same features

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19
Q

What is degenerate code?

A

This is when amino acids are coded for by more than one triplet of bases

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20
Q

What is an intron?

A

Non-coding sequences of DNA in a gene

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21
Q

What is an exon?

A

Sequences of bases that code for amino acids in a gene

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22
Q

Do prokaryotic cells contain introns?

A

No

23
Q

Why is the rate of replication faster in prokaryotic cells?

A

No membrane has to be synthesised

24
Q

How many different bases are there in DNA?

A

4 different bases

25
Q

How many different triplets are there and how is this number found?

A

64

4 bases ^3 = 64

26
Q

How is genetic code universal?

A

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

27
Q

What are triplets than do not code for an amino acid?

A

Nonsense triplets

28
Q

What are stop triplets?

A

Stop signals to terminate a protein chain

29
Q

Why does DNA need to be transcribed to RNA?

A

DNA confined to nucleus as too large to move through nuclear pores
Protein synthesis occurs in cytoplasm

30
Q

What is a codon?

A

Sequence of three bases of mRNA that codes for an amino acid

31
Q

Why are introns removed for protein synthesis?

A

To prevent gaps in the amino acid sequence which would cause gaps in the protein

32
Q

What is the difference between DNA & RNA?

A 
RNA is a single strand
Contains uracil (U) instead of thymine (T)
33
Q

What are the characteristics of messenger RNA (mRNA)?

A 
Single strand & single helix
Located in nucleus & cytoplasm
Bases: AUGC
Ribose sugar
Function: Transcription
34
Q

What are the characteristics of DNA?

A 
Double strand & double helix
Located in nucleus
Bases: ATGC
Deoxyribose sugar
Function: Hereditary material
35
Q

What are the characteristics of transfer RNA (tRNA)?

A 
Single strand & clover-leaf
Located in cytoplasm
Bases: AUGC
Ribose sugar
Function: Translation
36
Q

What is the function of transfer RNA?

A

Carries amino acids for proteins to ribosomes
Each tRNA has a specific sequence of three bases at one end, called an anticodon
They have an amino acid binding site

37
Q

What are the two main stages of protein synthesis?

A

Transcription

Translation

38
Q

What occurs in transcription?

A

DNA is used to synthesise a molecule of mRNA that will carry the code to the ribosomes

39
Q

Describe the transcription process

A

DNA helicase breaks hydrogen bonds and exposes nucleotides
RNA polymerase binds to promoter region and adds free nucleotides to form pre-mRNA
Stops once it reaches a stop region
pre-mRNA leaves the nucleus by the nuclear pores

40
Q

What is pre-mRNA?

A

Newly formed mRNA which contains exons and introns

Also contains promoter regions

41
Q

What is a promoter region?

A

Recognition sites for the RNA polymerase that indicate where to start copying the DNA

42
Q

What is splicing of pre-mRNA?

A

The removal of the introns and remaining exons are joined together
Ends of mRNA is “capped” which allows recognition which is required for translation

43
Q

How are amino acids joined to tRNA?

A

Using energy from ATP and a specific enzyme

44
Q

What organelle is required for translation?

A

Ribosomes

45
Q

What base sequence is always found on tRNA and why?

A

ACC

This is where amino acids bind

46
Q

Where does translation occur?

A

In the cytoplasm at the ribosomes

47
Q

What occurs in translation?

A

Amino acids are joined to create a polypeptide chain

This is done using the codons from mRNA to determine specific amino acids

48
Q

Describe the translation process

A

mRNA attaches to ribosome and tRNA carries amino acids to it
tRNA molecule with anticodon attaches to complementary bases on codon on the mRNA
This occurs with another tRNA and the amino acid from each are joined by a peptide bond
This continues until it reaches a stop codon

49
Q

What happens to the tRNA after the amino acid has formed a peptide bond with another in the ribosome?

A

It moves away from the ribosome

Leaves the amino acids behind

50
Q

How can the genetic code be described?

A

Non-overlapping
Degenerate
Universal

51
Q

Why is the genetic code described as non-overlapping?

A

As the base triplets don’t share their bases

52
Q

What is the role of RNA polymerase in transcription?

A

Join and attach nucleotides to form an RNA molecule

53
Q

Why can splicing cause a gene to code for different proteins?

A

The exons can be joined in different orders to produce different proteins

54
Q

Mutation of protein question answer

A

Change in DNA, base sequence, triplet
Different amino acids used to make a protein
Different sequence and primary to tertiary structure
Different tertiary means different bonds form
Protein has different shape
(enzymes active site changes so no enzyme-substrate complex can form)

A Level - Biology (22 decks)

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