Section 4 - Chapter 8: DNA, RNA, Photosynthesis Flashcards
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
2
Q
What is a locus
A
- The location of the gene on the strand of DNA/chromosome
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.
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
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
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
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 .
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
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.
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
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
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)
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.
14
Q
What is an allele
A
Different versions of a gene
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)
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
- mRNA is longer OR has more nucleotides than tRNA
- mRNA is a straight molecule but tRNA is clover-leaf shaped
- mRNA contains no paired bases/ hydrogen bonds but tRNA has
- mRNA has no amino acid binding site but tRNA does
- Many different mRNA only a few tRNA (20 or 64)
- tRNA has an anticodon, mRNA doesn’t
27
Q
EXAM QUESTION: Describe the role of tRNA in the process of translation(3)
A
- tRNA anticodon complimentary to codon
- tRNA brings specific amino acid
- Amino acids are carried/transferred to ribosome
- 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.
