4.1 DNA, genes and chromosomes Flashcards
Describe prokaryotic DNA.
CIRCULAR DNA:
- singular, circular chromosomal DNA
- not associated with histones
- double-stranded
- suspended in the cytoplasm
PLASMIDS:
- also may have one or more plasmids → genes for antibiotic-resistance often found in plasmids, only contains a few genes
Describe eukaryotic DNA.
- found in the nucleus
- associated with histones and other enzymes used in copying and repairing the DNA
- one very long, condensed DNA molecule
- tightly coiled combination of DNA and proteins is called chromatin – this is what chromatids, and therefore chromosomes, are made of
Is mitochondrial and chloroplast DNA similar to that of prokaryotes or eukaryotes?
Prokaryotes → endosymbiosis
What is a gene?
A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA molecule.
Describe how a gene is a code for the production of a polypeptide.
The base sequence in the triplet code determines the shape and behaviour of a protein molecule (the protein’s primary structure).
What are the functional RNA molecules?
The RNA molecules that are required for protein synthesis
mRNA - the base sequences on messenger RNA molecules are used by ribosomes to form polypeptide chains
tRNA - amino acids are carried to the ribosome by transfer RNA molecules
rRNA - ribosomal RNA molecules form part of the structure of ribosomes
What is a locus?
fixed position of a particular gene on chromosone
What is an allele?
Different forms of the same gene.
- they have different nucleotide sequences
- but they still occupy the same locus on the chromosome
What is a homologous pair of chromosomes?
Two chromosomes that carry the same genes
What is a triplet code?
A sequence of three bases that codes for one amino acid.
4 features of the genetic code.
-
Start codons and stop codons send signals that tell the cell where individual genes start and stop so it reads the DNA correctly (i.e. each base is only read once) - stops translation
2.degenerate: many codons can code for one amino acid
ADV: if mutation occurs in codon could still code for the same amino acid - universal: same codons code for the same amino acid in all organisms. ADV: genetic engineering is possible
- Non- overlapping: each codon is read as a discrete unit, each base is only apart of one triplet base. ADV: if mutation occurs only effects one codon and amino acid
What is an intron.
Non-coding DNA so does not code for any amino acids.
What is an exon.
DNA that codes for amino acids.
Where are non-coding multiple repeats found?
Between genes (positioned at the telomeres).
Where are introns found?
Within gene (between exons).
When are introns removed?
Splicing
How the structure of DNA relates to its function: (7 points)
- Double stranded: both strands act as a template for semi- conservative DNA
- Weak H bonds: can be unzipped for replication
- Complementary base pairing: allows identical copies to be made
- Double helix: makes DNA more compact, protects bases
- Long molecule: stores a lot of genetic info
- Phosphodiester bond: protects chemically reactive nitrogenous base
- Many H bonds between bases: protects bases, more stable.
DNA Vs RNA nucleotide
- DNA contains thymine whereas RNA contains uracil
- DNA contains deoxyribose pentose sugar whereas RNA contains ribose
DNA Vs RNA polynucleotides
- DNA is much larger, contains entire genome, whereas RNA is much shorter bc its the length of one gene
- DNA is double stranded, whereas RNA is single stranded
what is a gene?
a section of DNA that codes for making a polypeptide and functional RNA
what is a genome?
complete set of genes within a cell
what is a proteome?
full range of proteins that a cell is able to produce
what are chromosomes?
where the DNA is stored in eukaryotes
- 23 pairs, 46 chromosomes (23rd determines sex)
Eukaryotic DNA Vs Prokaryotic DNA
Eukaryotic:
- long
- wrapped
- linear
- chromosomes
Prokaryotic:
- short
- NOT bound by histones
- circular
- chromosomal DNA loop
