Reproduction, the Genome And Gene Expression Flashcards
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Chromosome
def
The structure made of DNA that codes for all the characteristics of an organism
Amino acid
def
The building blocks that make up the protein molecule
Code (biology)
def
A rule for converting one type of information into another, usually simpler or more complicated
Cytoplasm
def
The living substance inside a cell (not including the nucleus).
Diploid
def
A cell that contains two sets of chromosomes
Disease
def
Illness affecting plants and animals
DNA
def
Deoxyribonucleic acid. The material inside the nucleus of cells, carrying the genetic information of a living being
Double helix
The shape of the DNA molecule with two strands twisted together in a spiral
Environmental variation
def
Differences between individuals of a species due to factors in their surroundings
Fertilisation
def
The joining of a male and female gamete
Gamete
def
Sex cell (sperm in males and ova/eggs in females).
What is a Gene?
The basic unit of genetic material inherited from our parents. A gene is a small section of DNA in a chromosome. Each gene has the code for creating a specific protein. The sequence of bases in the gene controls which amino acids are joined in order to make a specific new protein (or enzyme) molecule. The proteins are then folded into their correct shape to make them functional.
Genetic
def
To do with inheritance because of genes
Genetic code
def
The code formed by the order of the bases in DNA that determines an organism’s characteristics
Genome
basic definition
The complete set of DNA found in an organism
Haploid
def
A sex cell (gamete) that contains one set of chromosomes
Heredity
def
Genetic information that determines an organism’s characteristics, passed on from one generation to another. To do with passing genes to an offspring from its parent or parents
Meiosis
def
Reduction division in a cell in which the chromosome number is halved from diploid to haploid
Mitosis
def
A type of cell division which produces daughter cells identical to the parent
Molecule
def
A collection of two or more atoms held together by chemical bonds
Mutation
def
A random and spontaneous change in the structure of a gene, chromosome or number of chromosomes
Nucleotide
def
The units or molecules of which DNA or RNA is composed
Nucleus
def
The nucleus controls what happens inside the cell. Chromosomes are structures found in the nucleus of most cells. The plural of nucleus is nuclei
Phenotype
def
The visible characteristics of an organism which occur as a result of its genes
Pollen
def
Male sex cell (gamete) from flowering plants
Polymer
def
A large molecule formed from many identical smaller molecules known as monomers
Protein
def
Organic compound made up of amino acid molecules. One of the three main food groups, proteins are needed by the body for cell growth and repair
Protein synthesis
def
The production of proteins from amino acids, which happens in the ribosomes of the cell.
Ribosome
def
The site of protein synthesis
Sexual reproduction
def
The formation of a new organism by combining the genetic material of two organisms
Species
def
A type of organism that is the basic unit of classification. Individuals of different species are not able to interbreed successfully
Variation
def
Difference between individuals, distance from the norm
Zygote
def
A fertilised egg cell.
what is sexual reproduction?
Sexual reproduction involves the joining of two sex cells, or gametes during fertilisation. Organisms produced by sexual reproduction have two parents and are genetically similar to both but not identical to either.
The advantages of sexual reproduction:
- it produces variation in the offspring
- the species can adapt to new environments due to variation, which gives them a survival advantage
- a disease is less likely to affect all the individuals in a population
- humans can speed up natural selection through selective breeding, which can be used, for example, to increase food production.
The disadvantages of sexual reproduction:
- time and energy are needed to find a mate
- it is not possible for an isolated individual
What is asexual reproduction?
Asexual reproduction only involves one parent so there is no joining of sex cells during fertilisation. Organisms produced by asexual reproduction are genetically identical to each other and their parent. They are clones.
The advantages of asexual reproduction include:
- the population can increase rapidly when the conditions are favourable
- only one parent is needed
- it is more time and energy efficient as you don’t need a mate
- it is faster than sexual reproduction.
The disadvantages of asexual reproduction include:
- it does not lead to variation in a population
- the species may only be suited to one habitat
- disease may affect all the individuals in a population
Name the 2 types of cell division and what they do.
overview/basic
There are two types of cell division called mitosis and meiosis. Mitosis produces identical diploid body cells for growth and repair. Meiosis produces haploid non-identical sex cells, or gametes. These fuse to form a diploid fertilised egg cell during fertilisation.
What does meiosis produce?
Meiosis produces sperm and egg cells in animals, and pollen and egg cells in plants.
Describe the process of meiosis.
During cell meiosis, the nuclear divisions that occur in two sets of chromosomes (one from each parent) result in the formation of four sex cells.
1) there is a parent cell
2) Chromosomes make identical copies of themselves
3) Similar chromosomes pair up
4) Sections of DNA get swapped
5) Pairs of chromosomes divide
6) Chromosomes divide
Describe the process of mitosis.
During cell mitosis, the nucleus of a “parent” cell divides into two new nuclei. Each one has the same number of chromosomes the parent cell’s nucleus had.
1) Chromosomes in nucleus are copied
2) The chromosomes are pulled apart and moved towards poles
3) Chromosomes separate
4) cells divide
DNA
detailed
The genetic material in the nucleus of a cell is made up of a chemical called DNA. DNA is a polymer, made of many smaller units called nucleotides. A nucleotide is made of a sugar and a phosphate group, with one of four different bases, A, C, T or G, attached. The nucleotides join together, forming two strands. These, in turn, form a double helix structure. The double helix is held together by weak hydrogen bonding between complementary base pairs. Base A always pairs with T, and C always pairs with G forming a twisted ladder structure called a double helix. It carries the genetic code, which determines the characteristics of a living organism.
Genome
detailed definition
The genome is one copy of all an organism’s DNA. In humans this is all the DNA that makes up the 23 pairs of chromosomes found in all diploid body cells. That is all the cells except sex cells or gametes, which only have half of a person’s genome.
What was the human genome project and what were its aims?
The Human Genome Project, or HGP for short, was started at the end of the last century. It was very ambitious and had several aims, including:
- to work out the order or sequence of all the three billion base pairs in the human genome
- to identify all the genes
- to develop faster methods for sequencing DNA
What did the human genome project do?
The sequencing project was finished in 2001, and work continues to identify all the genes in the human genome. The HGP used the DNA of several people to get a sort of average sequence, but each person has a unique sequence (unless they have an identical twin).
What are the results of the human genome project used for?
Mapping of a person’s genome can help in predicting how likely they are to develop certain conditions. Scientists and doctors are also now beginning to use the information they have discovered in the HGP to help make more effective medicines as the effectiveness of medicines can be affected by variations in alleles.
discovery of the structure of DNA
James Watson and Francis Crick worked out the structure of DNA in 1953. By using data from other scientists (Rosalind Franklin and Maurice Wilkins) they were able to build a model of DNA. The X-ray crystallography data they used showed that DNA consists of two strands coiled into a double helix.
What is DNA made of?
DNA is a polymer made from four different nucleotides. These are arranged in a repeating fashion. Each nucleotide consists of alternating sugar and phosphate sections with one of the four different bases attached to the sugar.
Base pairs
Each strand of DNA is made of chemicals called bases. Note that these are different to bases in relation to acids and alkalis in chemistry. There are four different bases in DNA:
- thymine, T
- adenine, A
- guanine, G
- cytosine, C
There are chemical bonds between the two strands in DNA, formed by pairs of bases. They always pair up in a particular way, called complementary base pairing:
- thymine pairs with adenine (T–A)
- guanine pairs with cytosine (G–C).
Making proteins from amino acids.
Each gene acts as a code, or set of instructions, for making a particular protein. Some of these proteins control the cell’s internal chemistry. They tell the cell what to do, give the organism its characteristics, and determine the way its body works.
To enable genes to code for proteins, the bases A, T, G and C get together - not in pairs - but in triplets. How does this work?
To enable genes to code for proteins, the bases A, T, G and C get together - not in pairs - but in triplets. This is how it works:
1) Each triplet of bases codes for one particular amino acid.
2) Amino acids are made in the number and order dictated by the number and order of base triplets.
3) The amino acid molecules join together in a long chain to make a protein molecule. The number and sequence of amino acids determines which protein is produced.
protein synthesis.
detailed
The DNA code for the protein remains in the nucleus, but a copy, called mRNA, moves from the nucleus to the ribosomes where proteins are synthesised in the cytoplasm. The protein produced depends on the template used, and if this sequence changes a different protein will be made.
Carrier molecules bring specific amino acids to add to the growing protein in the correct order. There are only about 20 different naturally-occurring amino acids.
Each protein molecule has hundreds, or even thousands, of amino acids joined together in a unique sequence. It is then folded into the correct unique shape. This is very important, as it allows the protein to do its job. Some proteins are enzymes, others are hormones and others form structures within the body, such as collagen. Each of these proteins needs a different shape.
How do cells express their genes?
Name the stages of this process.
Cells express their genes by converting the genetic message into protein. This process of protein synthesis occurs in two stages - transcription and translation.
Transcription
When a gene is to be expressed, the base sequence of DNA is copied or transcribed into mRNA (messenger RNA). This process takes place in the nucleus and occurs in a series of stages:
1) The two strands of the DNA helix are unzipped by breaking of the weak Hydrogen bonds between base pairs. This unwinding of the helix is caused by an enzyme (helicase enzyme).
2) The enzyme RNA polymerase attaches to the DNA in a non-coding region just before the gene.
3) RNA polymerase moves along the DNA strand. Free RNA nucleotides form hydrogen bonds with the exposed DNA strand nucleotides by complementary base pairing to form a strand of mRNA:
- Note - RNA nucleotides contain the same bases as DNA, except that T is replaced by U. U base pairs with A.
- Because the opposite base bonds with the exposed DNA bases, the strand of mRNA is an opposite copy of the DNA strand (except that U replaces T). We call this a complementary copy.
4) The newly formed strand of mRNA is now ready to leave the nucleus and travel to the ribosome.
Translation
1) The mRNA strand travels through the cytoplasm and attaches to the ribosome. The strand passes though the ribosome.
2) For every three mRNA bases the ribosome lines up one complementary molecule of tRNA. We call every three bases a codon.
3) tRNA molecules transport specific amino acids to the ribosome which they leave behind shortly after lining up opposite the DNA. Because there are three mRNA bases for each tRNA molecule, we call this the triplet code.
4) Used tRNA molecules exit the ribosome and collect another specific amino acid.
5) A chain of several hundred amino acids in the correct order according to the original DNA is then made. This is called a polypeptide.
After translation, the polypeptide is finally folded into the correct shape and becomes a protein. Peptide bonds form between the adjacent amino acids to finalise the structure.
non-coding regions
definition
Not all parts of the DNA code for proteins
Parts of our DNA which don’t make proteins.
it is believed that a human is made from only about 20,000 genes.
Effect of genetic variants on phenotype
However, there are sections of non-coding DNA which can switch genes on and off. Not all the genes you need to survive are needed throughout your life. Some regions of these non-coding DNA are not as good as binding to RNA polymerase. This means the enzyme is less likely to bind and so less protein is produced. If less protein is produce this can affect the phenotype of the organism.
In different cells around the body, certain genes will be switched on and others will be switched off. This will vary depending on which cells you examine.
Genetic causes of variation.
Every sperm and egg cell contains half of the genetic information needed for an individual. Each sex cell is known as haploid, which has half the normal number of chromosomes. When the chromosomes fuse during fertilisation, a new cell is formed, which is known as a zygote. It has all the genetic information needed for an individual, which is known as diploid and has the full number of chromosomes.
Examples of variation (in humans, caused by genetics)
- blood group
- skin colour
- eye colour.
- Whether you have lobed or lobeless ears is due to genetic causes.
- Sex is also an inherited variation - whether you are male or female is a result of genes you inherited from your parent.
Environmental causes of variation
Some examples of variation are not caused by the inheritance of genetics. Whether or not you have a scar or tattoo was not determined when the sperm fertilised the egg to begin your life. This variation is often caused by the environment we live in and so is called environmental variation.
Genetic and environmental causes of variation
Many kinds of variation are influenced by both environmental and genetic factors, because although our genes decide what characteristics we inherit, our environment affects how these inherited characteristics develop. For example:
- a person might inherit a tendency to be tall, but a poor diet during childhood will cause poor growth
- plants may have the potential for strong growth, but if they do not receive sufficient mineral resources from the soil, they may hardly grow at all
Identical twins are a good example of the interaction between inheritance and environment, because such twins are genetically the same. Any differences you may see between them – for example in personality, tastes and particular aptitudes – are due to differences in their experience or environment.
Types of data from surveys on variation
Variation in a population is often investigated by completing a survey. The data that is collected from this can be one of two types; name them.
Continuous variation and Discontinuous variation
What is continuous variation?
Continuous variation is variation that has no limit on the value that can occur within a population. A line graph is used to represent continuous variation.
What is Discontinuous variation?
Discontinuous variation is variation that has distinct groups for organisms to belong to. A bar graph is used to represent discontinuous variation.
Give examples of continuous variation.
- height
- weight
- heart rate
- hand span
- leaf length
Gives examples of discontinuous variation.
- blood group
- eye colour
- tongue rolling.
The causes and effects of mutations
Mutations are changes that can occur in genes. These changes are random and can be caused by background radiation and chemicals that we come into contact with, eg the chemicals in cigarette smoke. The change causes an alteration to the base sequence in the genetic code.
Sometimes these changes can be so severe that the cell dies, sometimes the cell can divide uncontrollably and become cancerous, and sometimes the changes are small and the cell survives. Occasionally, the changes may even be beneficial to us and produce new and useful characteristics.
Passing on mutations
If these changes occur in normal body cells, the changes are lost when we die. But if the changes occur in our sex cells such as sperm and ova, there is the possibility that the changes in the gene will be passed onto the next generation.
It is when these changes are passed on to the next generation that natural selection can either ensure that they are selected if they are useful, or disappear from the gene pool if they are not.
How many base pairs are in the human genome?
The are over three billion base pairs in the human genome.
Which base does Uracil replace in mRNA?
Thymine
