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biology > GENETIC INFORMATION, VARIATION AND RELATIONSHIPS BETWEEN ORGANISMS > Flashcards

GENETIC INFORMATION, VARIATION AND RELATIONSHIPS BETWEEN ORGANISMS Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is a gene?

A

A section of DNA that codes for making a polypeptide and functional RNA.
- polypeptides make proteins and so genes determine the proteins of an organism

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2
Q

What is a locus

A

The location of a particular gene on a chromosome is called the locus

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3
Q

What is the genetic code?

A

order of bases on DNA, consisting of triplet of bases each triplet base coding for a particular amino acid

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4
Q

What is an allele

A

Different versions of the same gene

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5
Q

What is a codon

A

More than 3 bases makes a codon and each codes for a different amino acid

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6
Q

What is an intron

A

Non coding section of DNA

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7
Q

Features of the genetic code

A
  1. NON OVERLAPPING - so each triplet is only read once and triplets don’t share any bases
  2. NON CODING - genes are separated by non coding repeats of bases
  3. DEGENERATE - more than one triplet codes for the same amino acid which reduces the number of mutations. Change in base sequence of DNA alters the amino acid sequence and the protein
  4. UNIVERSAL - With a few exceptions each triplet codes for the same amin acids in all organisms - indirect evidence for evolution
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8
Q

Describe eukaryotic cells DNA

A

DNA is longer and forms a linear line
Wraps around histones to form chromosomes
Mitochondria and chloroplasts also have their own DNA which is short and circular and not associated with proteins - these organelles were once free-living bacteria that were engulfed by a host cell. Mutually beneficial relationship so now live in symbosis

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9
Q

Describe prokaryotic cell DNA

A

DNA molecule is shorter and forms a circular loop and not associated with histones.
No chromosomes and bacteria also have plasmids

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10
Q

What is a chromosome

A

Thread like structure that is made of protein (histones) and DNA on which information is passed from one generation to the next

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11
Q

Chromosome formation

A

DNA polymer associates with proteins called histones which form long spirals of chromatin
Chromatin wraps up to form big data bases of information called chromosomes

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12
Q

Describe what a homologous pair is

A

We have 46 chromosomes in every cell in the body that are arranged into homologous pairs.
A homologous pair consists of two chromosomes that carry the same genes.
They are non identical as they can carry different alleles of the same gene.

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13
Q

What is the genome

A

complete set of genes present in a cell

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14
Q

What is a proteome

A

full range of proteins that a cell is able to produce
The proteome is usually larger than the genome of an organism due to the large amount of post-translational modification of proteins

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15
Q

Describe RNA

A
  • ribonucleic acid
  • shorter and less stable
  • bases = A/U C/G
    Made of a phosphate group, pentose sugar ribose and a nitrogen containing base
    3 TYPES:
    1. RNA that transfers genetic information from DNA to ribosomes (mRNA)
    2. RNA that makes up ribosomes along with proteins (rRNA)
    3. RNA involved in protein synthesis (tRNA).
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16
Q

mRNA

A

Name = messenger ribonucleic acid
Chain length = relatively short
Shape = single helix
Pentose sugar = ribose
Organic bases =uracil, guanine, cytosine, adenine
Chemical stability = least stable
Location = manufactured in nucleus but found throughout cell
Function = transfers information from DNA to ribosomes. Make up ribosomes with protein. Involved in protein synthesis

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17
Q

tRNA

A

Name = transfer ribonucleic acid
Chain length = shortest
Shape = clover shaped
Pentose sugar = ribose
Organic bases = uracil, guanine, cytosine, adenine
Chemical stability = less than DNA but more than mRNA
Location = manufactured in nucleus but found throughout cell
Function = transfers amino acids in order based on code on mRNA translation

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18
Q

Transcription

A
  1. Hydrogen bonds between complementary base break due to the actions of enzyme. DNA uncoils and separates the two strands exposing bases
  2. One DNA strand is used as a template to make the mRNA molecule. Template is called the antisense strands
  3. Free nucleotides are joined by phosphodiester bonds - forms a molecules of mRNa. RNA polymerase catalyses the formation of phosphodiester bonds. As RNA polymerase moves away the DNA rejoins with only 12 bases being exposed at a time to reduce the chance of damage to the DNA
  4. Pre mRNA is too large to fit through nuclear pore so splicing takes place which gets rid of introns leaving only the coding exon.
  5. mRNA atracted to ribosome in the cytoplasm
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19
Q

Translation

A

Occurs in the cytoplasm of the cell
1) mRNA associates with ribosome
2) ribosome moves to find the start codon (AUG)
3) tRNA brings specific amino acid and the anticodon on tRNA is complementary to the codon on mRNA
4) ribosome moves along to the next codon
5) process is repeated and amino acids are joined using energy from ATP to form a polypeptide

20
Q

What is a mutation

A

A change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide

21
Q

Why don’t some mutations alter the polypeptide for

A

Most mutations do not alter the polypeptide or only alter it slightly so that its structure or function is not changed
This is because the genetic code is degenerate

22
Q

insertion mutation

A

A mutation that occurs when a nucleotide is randomly inserted into the DNA sequence
An insertion mutation changes the amino acid that would have been coded for by the original base triplet, as it creates a new, different triplet of bases
- frameshift may occur

23
Q

what is a frameshift

A

when a mutation has a knock on effect by changing the triplets further on in the DNA sequence
- may dramatically change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function

24
Q

silent mutation

A

when substitution of a base still codes for the same amino acid as the original base
- only possible due to the degenerate nature of the genetic code

25
Q

substitution of bases

A

a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base. Could code for a different amino acid

26
Q

deletion of bases

A

occurs when a nucleotide is lost from the DNA sequence. Deleting a base can lead to the codons no longer being read properly. Due to the fact that the bases are read in triplets
- frameshift occurs

27
Q

Effect of gene mutations on polypeptides

A

A small number of mutations code for a significantly altered polypeptide with a different shape - may affect the ability of the protein to perform its function.
For example:
If the shape of the active site on an enzyme changes, the substrate may no longer be able to bind to the active site
A structural protein (like collagen) may lose its strength if its shape changes

28
Q

What is a mutagenic agent

A

Environmental factors that increase the mutation rate of cells
Examples include:
High-energy radiation such as UV light
Ionising radiation such as X rays
Toxic chemicals such as peroxides

29
Q

mutations in chromosome number (non-disjunction)

A

Non-disjunction occurs when chromosomes fail to separate during meiosis -
occurs spontaneously
Chromosome mutations involve a change in the number of chromosomes
An example of chromosome mutation is Down’s syndrome: Individuals with this syndrome have a total of 47 chromosomes in their genome as they have three copies of chromosome 21

30
Q

What is meiosis

A

form of cell division that produces 4 genetically different haploid cells known as gametes

31
Q

How does meiosis differ from mitosis

A

MEIOSIS:
1. Haploid cell
2. Two divisions
3. Genetic Variation

MITOSIS
1. Diploid cell
2. One division
3. Gentically identical cells

32
Q

describe what happens to chromosomes in meiosis

A
  1. chromosomes condense and associate in homologous pairs
  2. crossing over occurs
  3. chromosome join to spindle fibres at equator of the cell and join via a centromere
  4. homologous chromosome move to opposite pole and are separates
  5. pairs of chromatids move to opposite poles and are separated in 2nd division
33
Q

Meiosis I summary

A

Meiosis I:
Interphase (chromosomes replicate)
Prophase I (Homologous pairs form bivalents, crossing over, spindles form)
Metaphase I (Bivalents line up randomly, separation of maternal / paternal chromosomes)
Anaphase I (Homologous chromosomes pulled apart to poles of cell)
Telophase I (Cell divides by cytokinesis, spindle fibres disappear, nuclear membrane forms)

34
Q

Meiosis II summary

A

Meiosis II:
Prophase II (Spindle forms, nuclear membrane disappears)
Metaphase II (Chromosomes line up at equator, attached by centromere)
Anaphase II (Centromeres divide and chromatids separate)
Telophase II (Chromosomes reach end of cell, new nucleus forms, cells split via cytokinesis)

35
Q

What processes increase the genetic diversity of gametes produced

A

Meiosis has several mechanisms that increase the genetic diversity of gametes produced
Both crossing over and independent assortment (random orientation) result in different combinations of alleles in gametes

36
Q

independent assortment

A

Happens in metaphase I, when the bivalent line up on the equator. Each bivalent is made up of two chromosomes. The chromosomes can line up in any order on the equator resulting in different possible combinations
-When the chromosomes split, its random whether the maternal or paternal one lands up in the new cell)

37
Q

crossing over

A

Occurs in prophase I
While the two homologous chromosomes are joined in a bivalent, bits of one chromosome are swapped (crossed over) with the corresponding bits of the other chromosome
- There are always equal amounts crossed over so chromosomes stay the same length
Crossing over means that the maternal and paternal alleles can be mixed

38
Q

random fertilisation

A

This takes place when two gametes fuse to form a zygote
Each gamete has a unique combination of genes and any of the numerous male gametes can fertilise the egg
- Its random which gamete is used for fertilisation

39
Q

what is genetic diversity

A

the total number of different alleles in a population

40
Q

advantage of greater genetic diversity

A

greater genetic diversity the more likely that some individuals in a population will survive an environmental change due to a wider range of alleles - hence wider range of characteristics
= genetic diversity is a factor that enable natural selection to occur

41
Q

what are the principles of natural selection in evolution

A
  • random mutation can result in new alleles of a gene
  • many mutations are harmful but in certain environments the new allele of a gene might benefit its possessor leading to increased reproductive success
  • the advantageous allele is inherited by members of the next generation
  • as a result over many generations the new allele increases in frequency in the population
42
Q

what is selection

A

the process by which organisms that are better adapted to their environment tend to survive and breed while those that are less well adapted tend not to

43
Q

what is directional selection

A

selection may favour individual that vary in one direction from the mean of the population

44
Q

directional selection - antibiotic example

A

For example, antibiotic-resistant bacteria strains are becoming more common due to the overuse of antibiotics
The presence of antibiotics is a selection pressure
Mutations are occurring in bacteria populations randomly
1. A mutation arises that confers antibiotic resistance - it is a beneficial allele
2. Bacteria with this mutation are more likely to survive and reproduce
3. Most bacteria without the resistance mutation die
4. Over generations, this leads to an increase in the frequency of beneficial allele that produces antibiotic resistance

45
Q

what is a selection pressure

A

Environmental factors that affect the chance of survival of an organism are selection pressures
- For example, there could be high competition for food between lions if there is not plentiful prey available; this environmental factor ‘selects’ for faster, more powerful lions that are better hunters

46
Q

what is stabilising selection

A

may favour average individuals and preserves the characteristics of a population
-This means things stay as they are unless there is a change in the environment

47
Q

example of stabilising selection

A

fA classic example of stabilising selection can be seen in human birth weights
Very-low and very-high birth weights are selected against leading to the maintenance of the intermediate birth weights

biology (4 decks)

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