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A Level Biology Paper 1 > Section 4 - Chapter 8: DNA, RNA, Photosynthesis > Flashcards

Section 4 - Chapter 8: DNA, RNA, Photosynthesis Flashcards

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1
Q

What is a gene

A
  • A gene is a small section of DNA
  • This codes for the sequence of amino acids in a polypeptide or
  • functional RNA including ribosomal RNA and transfer RNA
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2
Q

What is a locus

A
  • The location of the gene on the strand of DNA/chromosome
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3
Q

What is genetic code

A
  • Sequences of nucleotide bases in DNA that codes for a specific order of amino acids to make a specific protein
  • The bases are in a codon
  • Each triplet codon codes for a specific amino acid.
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4
Q

Why did scientists suggest there must be a minimum of 3 bases that coded for each amino acid

A
  • There are only 20 different amino acids
  • Using a pair of bases (42) 16 not enough
  • 3 bases produce 64 which is enough
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5
Q

What does the base sequence provide the instructions for

A
  • A proteins primary structure
  • When a protein is in demand (enzyme, structural protein etc) the DNA is separated
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6
Q

What is the link between mRNA and DNA

A
  • mRNA code is derived from DNA code (not identical)
  • mRNA code is complementary to the DNA code
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7
Q

What are the features of genetic code

A
  • Degenerative - most amino acids are coded by more than 1 triplet
  • No-overlapping - each base sequence is read only once.
  • Universal- each triplet codes for the same amino acid in all organisms .
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8
Q

Why does much of the DNA in eukaryotes not code for polypeptides

A
  • Between genes there are non-coding sequences made of multiple repeats of base sequences.
  • There are non-coding sequences called introns
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9
Q

What is the difference between prokaryotic DNA and Eukaryotic DNA

A
  • In prokaryotic: shorter, form a circlular DNA and plasmids, not associated with protein molecules therefore no chromosomes.
  • In Eukaryotic: longer, form a line (are linear) rather than a circle, associate with proteins called histones to form chromosomes.
  • Mitochondria and chloroplasts also contain DNA like prokaryotic DNA = short, circular and not associated with protein.
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10
Q

What is the chromosome structure

A
  • Found in the nucleus, made of DNA, contains many genes
  • Are only visible when a cell is dividing as they have condensed
  • When first visible = appear as 2 strands joined at a single point (centromere). Each thread = chromatid
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11
Q

What does the picture on chromosome structure show

A
  • DNA is a double helix wound around histones to fix it in position
  • The DNA-histone complex is then coiled in a chromosome.
  • In this way a lot of DNA is condensed in a single chromosome
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12
Q

What are Homologous chromosomes

A
  • One of each pair comes from each parent
  • Corresponding pairs are called homologous pairs
  • Is always 2 chromosomes that carry the same gene (blood group) but not necessarily the same alleles of the gene (A, B)
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13
Q

During meiosis, how does each daughter cells recieve chromosomes

A
  • During meiosis, the halving of the number of chromosomes is done which ensures each daughter cells recieves 1 chromosome from each homologous pair.
  • When the haploid cells combine, the diploid state with paired homologous chromosomes are restored.
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14
Q

What is an allele

A

Different versions of a gene

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15
Q

How is the coded information on the DNA in the nucleus transferred so the cytoplasm where it is translated into proteins ?

A
  • It is transcribed into a single-stranded molecule called ribonucleic acid (RNA)
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16
Q

What are the different types of RNA

A
  • mRNA (messenger RNA) - transfers DNA code from the nucleus to the cytoplasm/ ribosome.
  • tRNA (transfer RNA) - Involved in proteinsynthesis from the mRNA
  • Ribosomal RNA (rRNA) - Makes up ribosomes along with proteins
17
Q

What does Codon, Genome and Proteome mean

A
  • Codon refers to the sequence of 3 bases on mRNA that codes for a single amino acid
  • Genome The complete set of genes in a cell or organism including in mitochondria and chloroplasts
  • Proteome - the full range of proteins produced by the organism (based on its genome) - proteins produced
18
Q

Compare structures of RNA and DNA

A
  • Shape : DNA - double stranded, twisted into double helix - held by hydrogen bonds, RNA - single stranded
  • Pentose sugar: DNA - Deoxyribose, RNA: Ribose
  • Bases: DNA - A,T,C,G, RNA - A,U,C,G
  • Size: DNA - Long, RNA - Relatively short
19
Q

What is mRNA

A
  • Long strand arranged in a single helix
  • The base sequence in mRNA is determined by the sequence of bases of DNA in a process called transcription
  • Once formed mRNA leaves the nucleus via pores in the nuclear envelope - enters cytoplasm - associates with ribosomes.
  • There it acts as a template for protein synthesis .
  • Its structure/ function = it possesses information in the form of codons. The codon determines amino acid sequence of polypeptide.
20
Q

What is tRNA

A
  • Transfer RNA
  • Single stranded chain folded into a clover leaf shape, with 1 end of the chain extending beyond the other.
  • This is the part of the tRNA to which an amino acid can easily attach .
  • At other end - sequence of 3 organic bases (anticodon).
21
Q

What are the complementary bases in RNA AND how is tRNA suited to its function

A
  • Guanine with cytosine
  • Adenine with uracil
  • tRNA anticodon attaches to mRNA complementary codon
  • Its structurally suited to function - of lining up of amino acids on the mRNA template during proteinsynthesis
22
Q

Comparison of DNA, mRNA and tRNA

A
  • Polynucleotide chain - DNA: Double, RNAs: Single
  • Size - DNA, mRNA, tRNA
  • Shape - DNA: Double helix, mRNA: single helix, tRNA: clovershaped
  • Pentose - DNA: deoxyribose, RNAs: ribose
  • Bases - DNA: T, RNA: U
  • Found - DNA: Nucleus, RNA: Manufactured in nucleus but found throughout the cell
  • Quantity: DNA: constant for all cells, except gametes, RNAs: varies and with metabolic activity
  • Stable - DNA, tRNA, mRNA - individual molecules broken down within a few days
23
Q

What is splicing

A
  • The DNA of a gene is made of exons - code for proteins and sections of introns that are non-coding sequences of DNA - Introns prevent synthesis of polypeptide
  • Base sequences corresponding to introns are removed and functional exons are joined - splicing
  • As most prokaryotic cells dont have introns - no splicing
24
Q

EXAM QUESTION: Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide chain

A
  • mRNA associates with a ribosome/ ribosome attaches to mRNA
  • Ribosome moves to find the start codon
  • tRNA carries a specific amino acids
  • Anticodon on tRNA complementary to codon on mRNA
  • Ribosome moves along to the next codon
  • Process repeated until a stop codon is reached and amino acids join by peptide bonds to form a polypeptide chain OR ATP that is hydrolysed to provide required energy
25
Q

EXAM QUESTION: Describe how mRNA is produces in a plant cell (5)

A
  • The DNA strands separate by breaking the H bonds
  • Only template strand is used to make mRNA
  • Complementary base pairing occurs
  • Adjacent RNA nucleotides joined by RNA polymerase
  • Pre-mRNA formed
  • Splicing/introns removed to form mRNA
26
Q

EXAM QUESTION: Give 2 differences between the structure of mRNA and the structure of tRNA (2)

A
  1. mRNA is longer OR has more nucleotides than tRNA
  2. mRNA is a straight molecule but tRNA is clover-leaf shaped
  3. mRNA contains no paired bases/ hydrogen bonds but tRNA has
  4. mRNA has no amino acid binding site but tRNA does
  5. Many different mRNA only a few tRNA (20 or 64)
  6. tRNA has an anticodon, mRNA doesn’t
27
Q

EXAM QUESTION: Describe the role of tRNA in the process of translation(3)

A
  1. tRNA anticodon complimentary to codon
  2. tRNA brings specific amino acid
  3. Amino acids are carried/transferred to ribosome
  4. Allows for correct sequence of amino acids along polypeptide

NOTE: DNA sequence order of mRNA codons, mRNA codons determines order of tRNA molecules. This determines order of amino acids

28
Q

What happens the polypeptide chain after translation

A
  • This depends on the protein made
  • The polypeptide chain is coiled or folded, producing its secondary structure
  • The secondary structure is folded, producing tertiary structure
  • Different polypeptide chains, along with any non-protein groups, are linked to form the quaternary structure.

A Level Biology Paper 1 (15 decks)

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