blueprint of life 2.4 Flashcards
describe the process of DNA replication and explain its significance
Step 1: The DNA double helix is unwound by an enzyme.
Step 2: The DNA unzips forming two single strands
Step 3: Nucleotides are added to the single strands
resulting in two identical
strands of DNA
During sexual reproduction, the genetic code is copied and then half of the genetic information passes into each of the sex cells (ovum or sperm). When fertilisation occurs the new organism has half the genetic material from each parent.
outline, using a simple model, the process by which DNA controls the production of polypeptides in three steps
There are two types of RNA that are involved in polypeptide synthesis, messenger RNA (mRNA) and transfer RNA (tRNA).
- In the nucleus, the double stranded DNA molecules unzip and the DNA code is transcribed into the single stranded mRNA molecule. The mRNA moves out of the nucleus into the cytoplasm and attaches to a ribosome. In the cytoplasm, the mRNA is translated into amino acids.
- At the ribosome, the messenger RNA lines up forming a template. A group of three bases, called a codon, codes for a specific amino acid. There are codes that start and stop the chain formation. AUG is the starting point for translation.
- tRNA has an anticodon (a non-amino acid forming codon) on one end and an amino acid on the other. A polypeptide is formed as each amino acid is added from tRNA to a chain following the sequence on the mRNA.
explain the relationship between proteins and polypeptides
A protein is made up of one or more polypeptides. A polypeptide is made up of a chain of many amino acids.
process information to construct a flow chart that shows that changes in DNA sequences can result in changes in cell activity
If there is a simple substitution for a single base pair on a strand of DNA such as a G-C replaced by A-T, then this will result in a different amino acid codon forming a different polypeptide. If one base pair is lost from the sequence there will be a shift along the DNA molecule producing different polypeptides
Cell activity is controlled by enzymes. Enzymes are formed from chains of polypeptides. If the chain of amino acids forming the polypeptide is not in the right sequence, then the enzyme formed will not be functional. In this case, there is a premature stop.
analyse information from secondary sources to outline the evidence that led to Beadle and Tatum’s ‘one gene – one protein’ hypothesis and to explain why this was altered to the ‘one gene – one polypeptide’ hypothesis
Beadle and Tatum used bread mould to investigate nutritional mutations. Using X-rays, they produced mould that was unable to produce a specific amino acid. The mould was unable to grow unless the amino acid was added. They showed that genes controlled biochemical processes.
Their hypothesis was that for each gene there was one enzyme or protein. The enzymes that they studied consisted of one polypeptide but many enzymes consist of chains of polypeptides. Therefore, the hypothesis has been changed to the “one – gene one – polypeptide” hypothesis.
explain how mutations in DNA may lead to the generation of new alleles
- Any change in the base sequence in DNA results in changes to the polypeptides that are produced and is a source of new alleles.
- To produce changes in alleles, the mutation must occur in the sex cells of the organism which are then passed on to the next generation.
discuss evidence for the mutagenic nature of radiation
A mutagen is a natural or human-made agent (physical or chemical) which can alter the structure or sequence of DNA. Mutagens can be carcinogens (cancer causing) or teratogens (birth defects causing).
Radiation was the first mutagenic agent known. Its effects on genes were first noticed in the 1920’s.When X-rays were first discovered, they were thought to be harmless and were a great novelty. You could even buy an “X-ray machine” for your home for entertainment. Most of the first generation of scientists who worked with radiation died of cancer. Famous examples are Marie Curie and her daughter who both died of leukaemia.
process and analyse information from secondary sources to explain a modern example of ‘natural’ selection
Modern examples include antibiotic resistance of bacteria and the insecticide resistance of insects. Look for similarities in the way that bacteria have become antibiotic resistant and insects have become insecticide resistant.
explain how an understanding of the source of variation in organisms has provided support for Darwin’s theory of evolution by natural selection
One of the foundation pillars for the theory of evolution is the variation that occurs among individual members of a species. The basis of this variation is the genetic makeup of the individuals in a species. It is this variation that selection acts upon. Mutation of DNA provides a source of new variations thus supporting Darwin’s theory of evolution.
describe the concept of punctuated equilibrium in evolution and how it differs from the gradual process proposed by Darwin
Punctuated equilibrium differs from Darwin’s gradual evolution in that evolution is seen as long periods where there is little change in organisms, followed by a shorter period where there are rapid changes. Evolution is a sudden process rather than slow gradual change. The evidence for this comes from the fossil record where there are mass extinctions of organisms followed by the appearance of new species.
what is DNA made up of
DNA is a double-stranded molecule twisted into a helix with each strand comprised of a sugar-phosphate backbone and attached bases - adenine (A), thymine (T), cytosine (C) and guanine (G) – connected to a complementary strand by pairing the bases, A-T and G-C.
