Mock Revision Topic 4 Flashcards
Describe how DNA is arranged in prokaryotes (2)
- DNA molecules are short, circular
- And not associated with proteins
Describe how DNA is arranged in eukaryotes (2)
- In the nucleus, DNA molecules are very long, linear
- And associated with proteins called histones
Name the organelles (other than the nucleus) which contain DNA and describe how it is arranged there (3)
- The mitochondria and chloroplasts of eukaryotic
cells also contain DNA - Which, like the DNA of prokaryotes, is short, circular
- And not associated with protein
What is a chromosome?
DNA molecule and its associated proteins
What is a gene and what does it code for? (3)
- A base sequence of DNA that codes for
- The amino acid sequence of a polypeptide
- A functional RNA (including ribosomal RNA and
tRNAs)
What is a locus?
The position a gene occupies on a particular DNA molecule
What is a triplet and what does it code for? (2)
- A sequence of three DNA bases
- Which codes for a specific amino acid
What is meant by saying that the genetic code is universal?
The same base triplets code for the same amino acids in all organisms (with some exceptions)
What is meant by saying that the genetic code is non-overlapping?
Each base is only read once as part of a specific triplet
What is meant by saying that the genetic code is degenerate?
Different base triplets or codons code for the same amino acid
What is an exon?
Sequences of DNA bases in a gene code for amino acid sequences
What is an intron?
Non-coding sequences of DNA bases in a gene (i.e. do not code for amino acid sequences)
What is the genome?
The complete set of genes in a cell
What is the proteome?
The full range of proteins that a cell is able to produce
Describe the similarities between mRNA and tRNA (3)
- Both polymers of nucleotides
- Nucleotides contain phosphate, ribose, adenine,
uracil, cytosine, guanine - Both contain phosphodiester bonds
Describe the differences between mRNA and tRNA (4)
- mRNA has a linear shape, tRNA has a clover leaf shape
- mRNA has no hydrogen bonds, tRNA does have hydrogen bonds
- mRNA is variable in length, tRNA is not variable in length
- mRNA has no amino acid binding site, tRNA has an amino acid binding site
How does transcription differ in pro/eukaryotes? (3)
- In prokaryotes, transcription results directly in the
production of mRNA from DNA - In eukaryotes, transcription results in the production of pre-mRNA
- This is then spliced to form mRNA
What is transcription and where does it take place? (8)
- In eukaryotes, transcription takes place in the nucleus
- Hydrogen bonds between DNA bases break
- One DNA strand acts as a template
- Free RNA nucleotides align by complementary base pairing
- In RNA, uracil base pairs with adenine on DNA ,or in RNA, uracil is used in place of thymine
- RNA polymerase joins adjacent RNA nucleotides
- By phosphodiester bonds between adjacent nucleotides
- Pre-mRNA is spliced to form mRNA (introns are removed)
What is the role of RNA polymerase? (3)
- Joins adjacent RNA nucleotides
- With phosphodiester bonds
- To form pre-mRNA
What is translation and where does it occur? Include the roles of tRNA and ATP (8)
- Translation occurs at the ribosome in the cytoplasm
- mRNA attaches to ribosomes
- tRNA anticodons bind to complementary mRNA codons
- tRNA brings a specific amino acid
- Amino acids join by peptide bonds
- With the use of ATP
- tRNA released after the amino acid is joined to polypeptide
- The ribosome moves along the mRNA to form the polypeptide
What is a gene mutation in general?
A change in the DNA base sequence of chromosomes
What is deletion?
The removal of one or more bases
What is substitution?
The replacement of one or more bases by one or more different bases
What is a mutagenic agent and what do they do? Include some named examples (6)
- They can increase the rate of gene mutation
- X-rays
- Gamma rays
- UV light
- Alpha and beta particles
- Benzene
Why might a substitution not cause a change in the sequence of encoded amino acids? (2)
- The genetic code is degenerate, more than one
base triplet could code for the same amino acid - So the polypeptide remains unchanged
What is genetic diversity?
The number of different alleles of genes in a population
What are the principles of natural selection? (7)
- Variation will already be present in a population due to random mutations which can result in new alleles of a gene
- Many mutations are harmful but, in certain environments, the new allele of a gene might benefit an organism
- Leading to increased reproductive success
- A change in the environment results in organisms with the advantageous allele for a particular phenotype being selected for as they are better adapted
- Organisms with the allele for this selected
phenotype survive and reproduce, passing on this beneficial allele - While those without this allele do not (differential reproductive success)
- Over many generations, the frequency of the advantageous allele increases in the population
What is directional selection? Include an example (3)
- This occurs when the environment is changing
- The change in the environment selects for those organisms with alleles for a phenotype towards
one extreme of a range - Such as antibiotic resistance in bacteria
What is stabilising selection? Include an example (6)
- This occurs when the environment is stable
- Organisms with alleles for characteristics towards
the middle of the range organisms survive - To reproduce and pass on their alleles to the next
generation - Organisms with alleles for the extremes of this
range are selected against - So are less likely to survive and reproduce so are less likely to pass on their alleles to the next generation
- Such as human birth weights
What is a species? (2)
- Organisms with similar characteristics
- Which can interbreed to produce fertile offspring
What is courtship behaviour and why is it necessary? (6)
- Acts as a necessary precursor to successful mating. It Allows organisms to:
- Recognise members of their own species
- Recognise members of the opposite sex
- Identify a mate who is capable of breeding (i.e. sexually mature, fertile and biologically fit)
- Synchronise mating so that it takes place when there is maximum probability of the sperm and egg meeting
- Form a pair bond that will lead to successful mating and raising of offspring
What is phylogenetic classification? Include an explanation of the term hierarchy and taxon (2)
- Hierarchy is where smaller groups are placed within
larger groups, with no overlap between groups - Each group a species is put into is called a taxon
List the taxa in order starting with the largest (8)
- Domain
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
