Biology Unit 1 Flashcards
Describe the structure of a nucleotide of DNA
Each base is attached to a phosphate molecule and a deoxyribose sugar molecule to form a nucleotide of DNA
What is the structure of nucleotides?
They join together in an anti-parallel structure to form a double-stranded helix
What type of bonds holds nucleotides together?
Strong covalent bonds
Describe the complementary base pairs and their properties
DNA bases only join with their complementary base pairs. Adenine to Thymine and guanine to cytosine.
What bonds hold complementary base pairs together?
weak hydrogen bonds.
What bonds hold the sugar-phosphate backbones in place?
Strong sugar-phosphate bonds
Describe the structure of deoxyribose sugar in terms of carbon no.
It contains 5 carbon molecules.
What are prokaryotes?
Cells that don’t possess membrane-bound organelles such as a nucleus. They have a singular, circular chromosome and smaller circular plasmids.
What are eukaryotes?
Cells AKA eukarya, that possess membrane-bound organelles such as a nucleus. They have linear chromosomes in the nucleus and circular chromosome in the mitochondria and chloroplast.
What are some examples of eukaryotes & prokaryotes?
prokaryotes ( bacteria and archaea) eukaryotes (Plant and animal cells)
Describe the way in which linear chromosomes (DNA) are packaged in eukaryotes
A strand of DNA must be condensed and packaged in order to fit the nucleus. Molecules of DNA are tightly coiled and packaged around bundles of proteins called histones.
What is DNA replication?
The process by which a double helix of DNA makes an exact copy of itself. This occurs immediately before mitosis
What are the stages of DR in detail?
Stage 1: DNA unwinds and the weak hydrogen bonds break b/n the bases, allowing the 2 strands to unzip into 2 template strands.
Stange 2: The 2 template strands produce a y-shaped replication fork.
Stage 3: Since DNA polymerase can assemble DNA only in the 5’ to 3’ direction the new complementary strand to the 3’ to 5’ direction strand must be assembled in short 5’ to 3’ segments which are later joined by ligase.
What are leading strands?
Leading strands (3’ end)- complementary DNA nucleotides are added continuously to make one new strand.
What are lagging strands?
lagging strands(5’ end) - complementary nucleotides of DNA make fragments which must be joined to make a new strand.
What are primers?
primers are short complementary sequences of nucleotides that are required at the start of a new strand. They only bind to the 3’end to begin the making of a new complementary strand.
Describe the formation of a leading strand process
The enzyme DNA polymerase adds complementary nucleotides to synthesise a complementary strand continuously from 5’ to 3’.
Describe the formation of a lagging strand?
-The formation of a lagging strand is discontinuous. Several primers (which are required by DNA polymerase to work with) are added to the replication fork as the DNA
unwinds.
- DNA polymerase adds the free complimentary nucleotides in fragments. The fragments are joined together by the enzyme ligase.
How is the process of DR done efficiently and quick?
During DR, many replication forks are formed at the same time to ensure the whole chromosome is replicated quickly and efficiently. Each replicated DNA molecule is composed of one original strand and one new strand
What’s the function of DNA template in DR?
The original strands of DNA form a nucleotide for the new complementary strands.
What’s the function of DNA polymerase in DR?
an enzyme which adds free nucleotides to make a new complementary strand or fragment.
What’s the function of free DNA nucleotides in DR?
to make the new complementary strands.
What’s the function of primers in DR?
needed for DNA polymerase to bind to. the start point of a new complementary strand or fragment.
What’s the function of ATP in DR?
energy is required for DNA replication.
What’s the function of ligase in DR?
an enzyme which joins the DNA of the lagging strand
What is the Polymerase chain reaction (PCR)?
The PCR is a technique used to create many copies of a fragment of DNA in an in vitro laboratory setting. Aka amplification of DNA meaning that a large quantity of the DNA fragment is made.
Describe the process of PCR
To begin the process of PCR, a DNA template strand is required.
Step1: the DNA is heated to 92-98 degrees Celcius.
-this breaks the weak hydrogen bonds b/n the bases and separates the DNA strands.
Step2:the DNA sample is cooled to 50-65 degrees Celcius.
-this allows short primers to bond to the separate DNA strands
Step3:the DNA sample is heated to 70-80 degrees Celcius.
-this allows heat-tolerant DNA polymerase to replicate the DNA by adding nucleotides to the 3’end of the original strand.
Why does during DR, one strand is replicated continuously while the other in fragments?
leading strand is synthesised continuously. DNA polymerase adds nucleotides to the deoxyribose 3’end strand in a 5’ to 3’ direction. the lagging strand is synthesised in fragments. nucleotides cannot be added to the phosphate 5’end cause DNA polymerase can only add DNA nucleotides in 5’ to 3’ direction. the lagging strand is therefore synthesised in fragments.
what are some practical used of PCR?
- classification of species
- diagnosis of genetic disorders
- to help solve crimes
- sex determination from a fetus before birth
- to settle paternity suits
what is gene expression?
is the process of using info from a gene to synthesise a protein.
how is a cell’s genotype determined?
by the sequences of bases in its genes.
how is a cell’s phenotype determined?
by the proteins that are synthesised when genes are expressed.
what are the 2 stages of protein synthesis?
transcription and translation
what is transcription?
the synthesis of mRNA from a section of DNA
what is translation?
the synthesis of protein using instructions from mRNA
what are the differences b/n DNA and RNA?
RNA is single-stranded whilst DNA is double-stranded. sugar in DNA is deoxyribose and in RNA it’s ribose. the base pairs in DNA is C-G A-T and in RNA it’s C-G A-U.
what are the 3 forms of RNA that are involved in transcription and translation
- mRNA (messenger RNA) carries a copy of the genetic code from the nucleus to the ribosome.
- tRNA ( transfer RNA) each tRNA molecule carries its specific amino acid to the ribosome
- rRNA (ribosomal RNA) forms ribosome with proteins
what is protein synthesis?
is a process in which instructions are carried from DNA sequences to the ribosome where the proteins are synthesised. mRNA is transcribed from DNA in the nucleus and then translated into proteins by ribosomes in the cytoplasm.
Describe the process of transcription of protein synthesis
- the enzyme RNA polymerase moves along the gene winding the double helix and breaking the hydrogen bonds b/n the bases.
- RNA polymerase synthesises a primary transcript of mRNA from free RNA nucleotides by complementary base pairs.
- RNA polymerase keeps adding nucleotides from the 5’end to3’end of the growing mRNA molecule until a specific sequence of nucleotides called stop codon is reached. The resulting mRNA molecule strand separates and is now called the primary transcript of mRNA.
What are codons?
Each triplet of bases on the mRNA molecule is called a codon and codons codes for amino acids. There are 21 amino acids in total. The different combinations of amino acids make the different proteins a cell needs
What are introns?
Introns are non-coding regions of the primary mRNA transcript and are removed
What are exons?
Exons are coding regions of the primary transcript (joined together) to form the mature mRNA transcript. The order of exons is unchanged during splicing. RNA splicing forms a mature mRNA transcript from the primary mRNA transcript exons are expressed
What is the idea behind alternative RNA splicing?
the same gene can be used to make several different proteins by treating different regions as introns and exons. This means the same primary mRNA transcript has the potential to produce several mature mRNA transcripts depending on which exons are expressed.
what is translation?
it’s the synthesis of a protein using the instructions from mRNA. The mRNA codons determine which amino acids will be joined together to make a particular protein.
What is tRNA?
it’s found in the cytoplasm and each molecule of tRNA has one triplet of bases called an anticodon. This is complementary to an mRNA codon and specific to an amino acid which is carried to the ribosome by tRNA for protein synthesis.
Describe the process of translation.
- the mature mRNA transcript attaches to a ribosome in the cytoplasm.
- the start codon begins protein synthesis
- complementary tRNA anticodons attach to the mRNA strand, bringing a specific amino acid to form the protein molecule.
- peptide bonds join the amino acid molecules. each tRNA molecule leaves the ribosome once then amino acids are attached.
- the stop codon ends the protein synthesis.
Describe specific features of protein structure.
- amino acids linked by peptide bonds to form polypeptide (proteins)
- polypeptide chains fold to form the 3D shape of a protein, held together by hydrogen bonds and other interactions b/n individual amino acids.
- this creates a large variety of shapes of proteins which determines their functions.
what is cellular differentiation?
the process by which cell-expresses certain genes to produce proteins characteristics for the type of cell. Allows a cell to carry specialised functions. Unspecialised cells can undergo differentiation to become specialised cells.
What are meristems?
regions of unspecialised cells in plants that can divide (self-renew) and differentiate.
What are stem cells?
regions of unspecialised cells in animals that can divide (self-renew) and differentiate.
what are the 2 forms of stem cells in animals?
- embryonic stem cells – from early stages of embryonic development
- tissue stem cells –found in tissues throughout the body
What does pluripotent mean?
cells (embryonic stem cells) in the very early embryo can differentiate into all the cell types that make up the organism and so are pluripotent. This means all the genes in embryonic stem cells can be switched on so the cells can differentiate into any type of cell
what does multipotent mean?
Tissue stem cells are involved in the growth, repair and renewal of cells found in that tissue and so are multipotent. this means they can differentiate into all types of cell found in that particular tissue type.
what are some therapeutic uses of stem cells?
involves the repair of damaged or diseased organs and tissues. E.g this includes corneal repair and the regeneration of damaged skin
what are research uses of stem cells?
- they can be used as model cells to study how disease develop or can be used for drug testing
- stem cells can self-renew under the right conditions in the lab. This can show how cells processes such as cell growth, differentiation and gene regulation work.
What are some arguments against using embryonic stem cells for ethical work?
The use of ESC can offer effective treatment for disease and injury but it involves the destruction of the embryo.
what is the genome?
the genome of an organism is its entire hereditary information encoded in DNA. A genome is made up of genes that code for proteins and other DNA sequences that don’t code for proteins.
What are genes (coding sequences)?
DNA sequences that code for amino acid sequences in proteins
what is the role of non-coding sequences?
- regulate transcription by turning genes on/off as regions of DNA activate RNA polymerase to bind to a coding region.
- can be transcribed into mRNA but not translated into a protein (eg tRNA and rRNA)
- have no function
What is mutation?
it’s a change in an organisms DNA which can result in no protein being synthesised or an altered protein being synthesised.
what is a single gene mutation?
gene mutations involve alteration of a DNA nucleotide sequence.
what are the 3 types of single gene mutation?
- substitution: a single nucleotide is replaced with a different nucleotide.
- insertion: a single nucleotide is added into a DNA sequence.
- deletion: a single nucleotide is removed from a DNA sequence.
what are the effects of substitution mutation?
an amino acid is changed when the protein is being made (missense) or the change can result in the early production of a stop codon, causing a shorter protein (nonsense).
what are the effects of insertion mutation?
all amino acids coded for after the mutation are affected as they are moved one base pair up (frameshift mutation)
what are the effects of deletion mutation?
all amino acids coded for after the mutation are affected as they are moved one base pair down (frameshift mutation)
what are the effects of missense?
- one amino acid is changed for another
- this may result in a non-functional protein or it could have little effect on the protein
what are the effects of nonsense?
- a codon that is used to code for an amino acid changed to a stop codon
- a shorter protein will be produced
what are the effects of frameshift mutation?
-can cause all of the codons and all of the amino acids after the mutation to be changed. this has a major effect on the structure of the protein produced.
what are the effects of splice site mutation?
- if a mutation occurs at a splice site the codon for the intron may be affected. the intron may be retained or an exon may be cut out.
what is chromosome structure mutation?
some mutations affect the structure or no. of chromosomes and can often be lethal.
what are the 3 types of chromosome structure mutation?
- duplication: genes from one chromosome attach to it homologous partner
- deletion: the chromosome breaks in 2 places and the middle segment is detached.
- inversion: the chromosome break in 2 and the segment turns around and reattaches.
- translocation: a chromosome section breaks off and attaches to another chromosome.
what is evolution?
evolution is the change in organisms over generations as a result of genomic variation.
what is natural selection?
it’s the non-random increase in the frequency of DNA sequences that increase survival and the non-random reduction in the frequency of deleterious (harmful) sequences.
what are the main types of selection?
- stabilising
- directional
- disruptive
what is stabilising selection?
an average phenotype is selected for and extremes of the phenotype range are selected against. Meaning there is a smaller range of values, so less variation in the population, as having the average phenotype gives the organism a selective advantage
what is directional selection?
one extreme of the phenotype range is selected for as it gives a selective advantage. meaning there is still a range of values but the average value has changed. the advantageous trait that was initially rare is now common.
what is disruptive selection?
2 or more phenotype are selected for. the population is split into 2 or more distinct groups with different characteristics.
what are the effects on the population by the three types of selection?
- stabilising: a smaller range of values
- directional: new average. an extreme characteristic is now more common.
- disruptive: new average. the old average is common
what are the 2 ways in which gene can be transferred?
- vertical gene transfer
- horizontal gene transfer
what is horizontal gene transfer?
Genes are transferred b/n individuals of the same generation. Prokaryotes and viruses exchange genetic material this way. Prokaryotes can inherit genomic sequence horizontally by transferring genes b/n individuals of the same generation. this results in evolutionary change faster than organisms that only use vertical transfer.
what is verticle gene transfer?
genes are transferred from parent to offspring as a result of sexual or asexual reproduction.
what is speciation?
it’s the generation of new biological species by evolution as a result of isolation, mutation, natural selection, speciation.
describe the process of speciation briefly.
An isolation barrier splits a population into sub-populations.
mutation takes place in both sub-populations
natural selection acts on both of the new sub-population
speciation has taken place.
what are the three types of an isolation barrier
Isolation barriers prevent the flow b/n sub-populations during speciation. 3 types include geographical barriers, behavioural barriers and ecological barriers.
what is a geographical barrier?
this is the separation of a population by natural features such as rivers and mountains. This results in allopatric speciation
what is a behavioural barrier?
where two species are capable of interbreeding but don’t since they have difference in reproductive strategies that involve behaviour. this is known as sympatric speciation.
what is an ecological barrier?
this is separation by ecological niches such as pH levels, salinity or breeding locations differing between populations. this results in sympatric speciation.
what are the 2 forms of speciation?
- allopatric speciation: the population become isolated due to geographical barriers such as mountains or rivers physically separating them.
- sympatric speciation: the populations live in close proximity in the same environment but they have become isolated due to behavioural or ecological barriers.
Describe the full effect of allopatric speciation to finally speciation.
- a species is separated by a geographical barrier
- gene flow is prevented b/n sub-populations
- mutations occur randomly in each sub-population leading to new variation in each sub-population
- natural selection acts on each sub-population. different traits are favoured depending on selection pressures.
- the sub-populations become so genetically different that they could no longer interbreed, speciation has taken place
Describe the full effect of sympatric speciation to finally speciation.
- a large population of one species occupy the same environment
- some members of the population occupy alternative ecological niches and breed.
- 2 populations exploit different resources and no longer interbreed
- mutations produce new variation in each group
- new traits caused by mutations are passed on if they give a selective advantage
- over generations that results in 2 genetically distinct species, speciation has taken place
What is bioinformatics?
it’s the name given to the fusion of molecular biology, statistical analysis and computer technology to map and analyse DNA sequences.
how is bioinformatics used in biology/science?
it can be used to investigate evolutionary biology, inheritance and personalised medicine.
what can computer programmes be used to do?
they can be used to identify base sequences by looking for sequences similar to known genes and to compare DNA of sequence.
why is genomic sequencing used for?
it’s used to cut up the chromosome with the unknown DNA into fragments which are sequenced. Once the order of bases is known for each of the DN fragments they can be matched up to make an overall sequence using a computer. This allows the sequence of individual genes and entire genome to be determined.
what is comparative genomics used for?
- comparing members of different species e.g disease-causing microorganisms
- comparing members of the same species e.g E.coli
- comparing cancerous cells with normal cells
what does highly conserved mean?
it means that the gene has remained relatively unchanged through cycles of natural selection
what can highly conserved DNA sequences be used for?
they can be used by scientists to determine the relationship between species.
what is phylogenetics?
it’s the evolutionary history of relationships. The more similar the sequences are the more closely related the 2 organisms are. *2 species are more closely related to each other if they have a more recent ancestor.
what can fossil evidence be used for?
fossil evidence can be used to establish the sequence of events in evolution. this allows us to look at the last common ancestors of a species. RNA sequences are mostly used in phylogenetics.
which cell types contain the following features:
- true membrane-bound organelle
- membrane-enclosed organelles
- introns
- no. of types of RNA polymerase
- normal response to streptomycin.
BACTERIA :
- -true membrane-bound organelle (ABSENT)
- membrane-enclosed organelles (ABSENT)
- introns(ABSENT)
- no. of types of RNA polymerase(ONE)
- normal response to streptomycin.(GROWTH INHABITED)
ARCHAEA:
- true membrane-bound organelle (ABSENT)
- membrane-enclosed organelles(ABSENT)
- introns(PRESENT IN SOME SEQUENCES)
- no. of types of RNA polymerase(SEVERAL)
- normal response to streptomycin.(GROWTH INHABITED)
EUKARYOTES:
- true membrane-bound organelle (PRESENT)
- membrane-enclosed organelles(PRESENT)
- introns(PRESENT)
- no. of types of RNA polymerase(SEVERAL)
- normal response to streptomycin.(GROWTH INHABITED)
what are molecular clocks used to show?
it’s used to show when a species diverged during evolution
how does molecule clocks work?
- they assume a constant rate of mutation and show differences in DNA or amino acid sequences
- difference in sequence data show the time of divergence from a common ancestor
