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AQA A Level Biology > 4-8 DNA, Genes + Protein Synthesis > Flashcards

4-8 DNA, Genes + Protein Synthesis Flashcards

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1
Q

What is the structure of RNA?

A

ribose, organic base, phosphate group

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2
Q

Role of RNA

A

transfers genetic info from DNA to ribosomes for protein synthesis

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3
Q

WHat is the genetic code?

A

the order of bases on DNA consist of codon (triplets of bases that code for particular amino acids)

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4
Q

What are main features of genetic code?

A

non overlapping, degenerate - more than one triplet for each, universally - sequences used by all species

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5
Q

What is a gene?

A

a section of DNA that contains the coded information for making polypeptides and Functional RNA

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6
Q

What is a locus?

A

the fixed position on a DNA molecule occupied by a gene

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7
Q

What is an allele?

A

different forms of a particular gene found at the same locus on a chromosome, a single gene could have. many alleles

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8
Q

What are exons and introns?

A

exons - regions of DNA that code for amino acid sequences, separated by one or more introns
introns - regions of DNA that don’t cod eanything

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9
Q

What is a codon/

A

a sequence of three nucleotides that form a unit of genetic code

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10
Q

What is the structure of a chromosome?

A

DNA molecules twist and coil combining with histone molecules, twist and form loops, which coiil and loop again to form chromosomes

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11
Q

What are homologous chromosomes?

A

a pair of chromosomes with the same gene sequence - one from each parent

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12
Q

what is a genome?

A

the complete set of info contained in the cells of an organism

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13
Q

What is a proteome?

A

the complete set of proteins that can be produced by cells

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14
Q

What is mRNA?

A

messenger RNS - long single strand, complementary to DNA transcribed from

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15
Q

Why use mRNA for translation over DNA?

A

shorter, contain uracil, quick breakdown, single strand, no introns

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16
Q

What is tRNA?

A

transfer RNA, single strand of over 80 nucleotides folded into clover shape, anticodon on one end, amino acid binding site on other

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17
Q

What is transcription?

A

mRNA produced - in the nucleus - DNA uncoils exposed bases as template, joined by RNA polymerase

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18
Q

What is pre-mRNA splicing?

A

removal of introns preventing the sysnthesis of polypeptide

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19
Q

What is translation?

A

proteins produced, in cytoplasm, anticodon of tRNS attaches to complementary bases of mRNA, amino acids bonded to tRNA form peptide bonds, form until stop codon, requires ATP

20
Q

How do you synthesise a polypeptide?

A

a ribosome attches to the starting codon, a tRNA molecule with the complementary anticodon sequences, two amino acids joined by peptide bond using enzye and ATP until stop codon reached

21
Q

How do you assemble a protein?

A

the polypeptide is coiled (secondary), then folded held by H bonds (tertiary), then different chains are linked (quaternary)

22
Q

Why is it necessary for three bases to code for one amino acid?

A

Only 20 different amino acids regularly occur in proteins
Each amino acid must have its own code of bases on the DNA

There are only four different bases that are present in DNA
If each base coded for a different amino acid only four different amino acids could be coded for
Using a pair of bases, 16 different codes are possible which is still inadequate
Three bases produce 64 different codes which are more than enough to create 20 amino acids

23
Q

What is a DNA triplet?

A

Each amino acid is a triplet, consisting of 3 bases
There are 64 possible triplets so some amino acids are coded for by more than one triplet

A triplet is always read in one particular direction along the DNA strand
Three triplets don’t always code for an amino acid- some are stop codes which mark the end of a polypeptide chain

24
Q

What is degenerate code?

A

Because most amino acids are coded by more than one triplet

25
Q

How is the DNA code universal?

A

The code is universal with a few minor exceptions as each triplet codes for the same amino acid in all organisms

26
Q

How are introns/exons different in eukaryotic and prokaryotic cells?

A

Introns are more likely to be in eukaryotic cells

Prokaryotes do not have noncoding DNA so splicing does not occur

27
Q

How do introns and exons affect protein synthesis?

A

Introns should not be transcribed or translated

Splicing is when exons are copied, introns are removed

28
Q

What is mRNA?

A

RNA that transfers the DNA code from the nucleus to the cytoplasm
Short for messenger RNA

Small enough to leave the nucleus though the nucleus pores and to enter the cytoplasm

29
Q

What is a codon?

A

A sequence of three bases on mRNA that codes for a single amino acids

30
Q

What is the proteome?

A

The full range of proteins produced by the genome
Sometimes called the complete proteome, in which case the proteome refers to the proteins produced by a given type of cell under a certain set of conditions

31
Q

What is the structure of RNA?

A

Polymer made of repeating mononucleotide sub-units which forms a single strand
Nucleotide structure:

Pentose sugar ribose
One of the organic bases (A, G, C, U)
A phosphate group

32
Q

What are the two types of RNA?

A 
Messenger RNA (mRNA)
Transfer RNA (tRNA)
33
Q

What is the structure of mRNA?

A

Consists of thousands of mononucleotides
Long strand arranged into a single helix

Base sequence is determined by the base sequence of DNA in transcription

34
Q

What occurs during protein synthesis in terms of mRNA?

A

An anticodon pairs with the three complementary organic bases that make up the codon on mRNA

35
Q

What are the characteristics of DNA?

A

Double polynucleotide chain
Larger than mRNA and tRNA

Double helix
Pentose sugar is deoxyribose
Organic bases: A, G, C, T
Found mostly in the nucleus
Quantity is constant for all cells of a species except gametes
Chemically very stable
36
Q

What are the larger steps of protein synthesis?

A

DNA provides the instructions in the form of a long sequence of bases
Transcription: pre mRNA is formed

Splicing: Pre-mRNA is spliced to form mRNA
Translation: mRNA is used as a template

37
Q

What is transcription?

A

The process of making pre-mRNA using DNA as a template

38
Q

What are the steps of transcription?

A

DNA helicase breaks hydrogen bonds between the organic bases to expose the nucleotide bases
One strand acts as a template

The template pairs with complementary nucleotides present in the nucleus except for A links to U
RNA polymerase moves along the strand and joins nucleotides together to form a pre-mRNA molecule
RNA polymerase adds nucleotides one at a time
DNA strands rejoin behind the pre-mRNA
When a stop code is reached by polymerase, it detaches and the pre-mRNA is formed

39
Q

What are the steps of splicing?

A

Pre-mRNA is spliced to form mRNA

Introns, which don’t code for proteins, are removed and the functional exons are joined together

40
Q

Do eukaryotic or prokaryotic cells undergo splicing?

A

Eukaryotic: contain introns so splicing is required
Prokaryotic: do not contain introns so splicing is unnecessary

41
Q

What is translation?

A

Translating codons on the mRNA into a sequence of amino acids to make up a polypeptide

42
Q

What is tRNA?

A

A molecule with a specific anticodon and attaches to a specific amino acid

43
Q

What are the steps of translation?

A

Ribosome becomes attached starting codon
tRNA molecule with complementary anticodon pairs up with the mRNA codon

Next codon is paired up with the complementary anticodon and so on
Each tRNA molecule carries an amino acid
Ribosome moves along the mRNA, forming one peptide bond at a time between amino acids
Any amino acids behind the ribosome have been joined and leave the tRNA molecule
The free tRNA molecule picks up another amino acid from the amino acid pool
This allows many chains to be produced at once
The polypeptide chain grows until a stop codon is reached and the chain seperates

44
Q

How is a protein produced from a polypeptide chain?

A

Polypeptide is folded to form the secondary structure
Secondary structure is folded to to produce the tertiary structure

Polypeptide chains are joined together to form a quaternary structure

45
Q

What is the role of ATP during translation?

A

Required to provide energy to attach amino acids to tRNA

To form peptide bonds between amino acids

AQA A Level Biology (19 decks)

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