DNA, genes, chromosomes Flashcards
name the fixed position occupied by a gene on a DNA molecule (1)
locus
describe how a gene is a code for the production of a polypeptide (3)
- 3 bases
- in a triplet
- determines order of amino acid sequence
define exon (1)
base sequence coding for polypeptide
define non coding base sequences and describe where the non coding multiple repeats are positioned in the genome (2)
- DNA that does not code for protein
- positioned between genes
give 3 ways in which DNA in chloroplasts is different from DNA in the nucleus (3)
in chloroplasts DNA is shorter,
there are fewer genes
DNA is circular not linear
DNA not associated with histones
compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells (5)
comparisons:
1. nucleotide structure is identical
2. nucleotides joined by phosphodiester bonds
3. DNA in mitochondria same to DNA in prokaryotes
contrasts:
4. eukaryotic DNA is longer
5. eukaryotic DNA contain introns, prokaryotic DNA does not
6. eukaryotic DNA is linear, prokaryotic DNA is circular
7. eukaryotic DNA associated with histones, prokaryotic DNA is not
what is a homologous pair of chromosomes (1)
two chromosomes that carry the same genes
define a gene (3)
- a base sequence of DNA
-that codes for a functional RNA
-and codes for the amino acid sequence of a polypeptide chain
define proteome (1)
the full range of proteins that a cell is able to produce
define genome (1)
the entire set of genes in a cell
describe how DNA is replicated (6)
- DNA helicase
- breaks hydrogen bonds to separate strands
- both strands act as template
- free nucleotides attach
- by complementary base pairing
- DNA polymerase joins nucleotides
- hydrogen bonds reform
what is a gene (1)
- a base sequence of DNA that codes for a polypeptide
the change in proportion of DNA containing heavy N is due to the way DNA replicates- explain how (2)
- strands separate
- each acts as a template
- 1 strand in new molecule
- new strands made of light N
describe the structure of DNA and the structure of a chromosome (6)
- DNA is double stranded- held together by H bonds
- DNA is a polymer of nucleotides
- nucleotides joined together by phosphodiester bonds
- complementary base pairing between A and T, C and G
chromosome:
5. DNA associated with histones
6. chromosomes consist of 2 chromatids joined at centromere
define phenotype (2)
- an expression of the genes
- and interactions with the environment
explain why DNA polymerase can only attach nucleotides to the OH group on the 3 carbon molecule
enzymes are specific
active sites of a specific shape that fits their substrate
shape of 3’ end of the molecule with the OH fits the active site of DNA polymerase but the shape of 5’ end does not fit
What is a gene?
[1 mark]
A sequence of DNA (nucleotide) bases that
codes for a polypeptide;
Describe how the production of messenger RNA (mRNA) in a eukaryote cell is
different from the production of mRNA in a prokaryote cell.
- Pre-mRNA (only) produced in eukaryote (cell);
- Splicing (only) occurs in eukaryote (cell);
Scientists produced a short, single-stranded, artificial nucleic acid, called PNA.
The PNA binds to a section of DNA.
The scientists introduced PNA into cells and discovered that these cells produced
less mRNA than cells that did not contain PNA.
Suggest how PNA affected the transcription of the section of DNA.
[2 marks]
- PNA is complementary to DNA
- Preventing/reducing RNA polymerase
activity/binding
distinguish between a codon and an anticodon (1)
- codon is a triplet on mRNA and codes for an amino acid
- anticodon is a triplet on tRNA that is complementary to the codon on mRNA
state the function of a histone (1)
fixes the DNA into position
explain how the length of DNA is compacted into a chromosome (1)
it is looped and coiled many times
a strand of mRNA has 64 codons but the protein it makes has only 63 codons- suggest a reason for this difference (1)
stop codon does not code for an amino acid.
define genome (1)
the complete set of genes in an organism
